Testosterone Replacement Therapy (TRT): The Definitive Guide

What is testosterone replacement therapy (TRT)?

Testosterone replacement therapy, or TRT, is prescribed testosterone for men whose own testosterone is low. The aim is to bring the blood level back into the normal range and relieve the symptoms low testosterone causes, such as a low sex drive. It is a long-term treatment with regular blood tests, not a short course. [3], [4]

Testosterone is made mainly in the testicles, on instructions from the brain. When that system fails, doctors call it hypogonadism. The US Food and Drug Administration (FDA) has approved testosterone products for men with low testosterone plus an associated medical condition, such as damaged testicles or a pituitary problem, and none for low testosterone without one. [1]

Whether TRT suits older men whose testosterone has drifted down without a clear cause is the long-running argument. Every current US label still says safety and benefit in "age-related" low testosterone have not been established. On June 18, 2026, the FDA asked makers to remove that limitation, but no label had changed by September 2026. [2], [21], [20]

The hormone itself is not new. Leopold Ruzicka, who shared the 1939 Nobel Prize in Chemistry, showed that testosterone could be made from cholesterol. [22]

How common is low testosterone?

Much less common than a single blood test suggests. How many men "have low T" depends on whether you count a lab number alone or a lab number plus symptoms:

• Low number only. In a US community study of men aged 30 to 79, 24% had a total testosterone below 300 ng/dL, but only 5.6% met the study's stricter definition: low total and free testosterone plus specific symptoms. Among men over 50 with a low level, 47.6% had no symptoms at all. [23]
• Strict definition. In the European Male Ageing Study of men aged 40 to 79, only three symptoms tracked closely with low testosterone: fewer morning erections, low sexual desire and erectile problems. With those three symptoms plus a low total and free testosterone, 2.1% of men qualified, rising from 0.1% in their 40s to 5.1% in their 70s. [24], [25]
• With age. Following the same men over time, total testosterone fell by 1.6% a year in the Massachusetts Male Aging Study, and its authors suggest that new illness may speed the fall. [26] In a separate study of older men who reported very good health, average testosterone did not differ with age while obesity lowered it, so much of the difference between men tracks weight and health rather than age alone. [27]

The common claim that testosterone falls every year "after 30" does not come from these studies, which followed men from their 40s. The low testosterone guide covers symptoms and causes in full.

TRT: the key numbers

Testosterone for men comes in five main forms: injections, skin gels and creams, capsules, a nasal gel and pellets. This table shows each one's route, how often it is used and its typical labeled dose, checked in September 2026. Each form has its own guide with the full protocol and label details. [28]

[28], [29], [30], [11], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [3], [41], [2], [12], [42], [43], [44]

No longer sold in the US (checked September 2026): Striant (a gum-side tablet), the Androderm patch and the Axiron and Fortesta brands have been discontinued; generic 2% solutions remain. [45], [46], [47], [48]

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How often each form of testosterone is used

Labeled schedule for each form, from several times a day to every few months.

Each line runs from several times a day (left) to every 6 months (right); ticks mark daily, weekly and 4 weeks. Filled marks are labeled schedules; open circles are guideline examples or the Canadian start.

Natesto nasal gel (into the nose)

3 times a day (US); starts twice a day in Canada

Oral testosterone undecanoate (Jatenzo, Kyzatrex, Tlando)

Twice a day, with food

Gels, cream and 2% solution (on the skin)

Once a day (cream: AndroForte 5 in Australia)

Xyosted (enanthate under the skin)

Once a week

Cypionate or enanthate vials (into a muscle (US labels))

Label: every 2–4 weeks · guideline examples weekly or every 2 weeks

Sustanon 250 (four esters (UK, Australia))

Usually every 3 weeks

Undecanoate injection (Aveed (US), Nebido (UK))

Aveed every 10 weeks after 2 starting doses · Nebido every 10–14 weeks

Testopel pellets (under the skin of the hip)

Every 3–6 months

Labeled schedules; prescribers adjust with blood tests. Checked September 2026.

The practical differences are how often you dose, how much the level swings between doses, how much red blood cells rise (in pooled trials the average rise was largest with cypionate or enanthate injections and oral undecanoate, but only the gap between injections and skin patches was clear) and, for gels, the risk of passing testosterone to a partner or child by skin contact, which carries a boxed warning on every US gel. [49], [34] The cypionate vs enanthate guide compares the two most common injections.

How do injection doses turn into mL and syringe units?

Injection doses are written in milligrams (mg) and measured in milliliters (mL). The Endocrine Society's example starting schedules for cypionate or enanthate are 75 to 100 mg weekly, or 150 to 200 mg every 2 weeks, and the American Urological Association (AUA) prefers smaller weekly doses such as 100 mg weekly. [4], [3]

To turn a dose into a volume, divide by the vial's strength. For example, 100 mg from a 200 mg/mL vial is 0.5 mL, which is 50 units on a U-100 insulin syringe. From a 100 mg/mL vial, the same 100 mg is 1 mL. Doserly's TRT dose calculator works through each step. These are labeled and guideline doses; prescribers adjust them using blood tests and symptoms. The TRT dosage guide covers split schedules and dose changes.

Testosterone for women uses different products and far smaller doses. See testosterone therapy for women.

What testosterone level counts as low, and what is the target?

This table shows the numbers each major guideline uses, checked in September 2026. Labs in the US report testosterone in ng/dL; most other countries use nmol/L (1 nmol/L is about 28.8 ng/dL).

[3], [4], [50], [5], [51], [52], [53], [54], [14]

Most guidelines diagnose low testosterone somewhere between about 264 and 350 ng/dL (9.2 and 12 nmol/L), always with symptoms and always on repeated morning tests. They differ because they rest on different lab methods and evidence: the Endocrine Society's 264 ng/dL is the lower limit of normal in healthy young men measured with standardized assays, the EAU calls 12 nmol/L a reliable threshold for diagnosis, and the UK Society for Endocrinology notes little evidence of benefit from treatment above 12 nmol/L. No guideline diagnoses low testosterone from a single test or from a number alone. [4], [5], [54]

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Where guidelines draw the line for low testosterone

Total testosterone below which each body supports a diagnosis, with symptoms.

Each line runs from 200 ng/dL (7 nmol/L, left) to 400 ng/dL (14 nmol/L, right); the shaded part is 264–350 ng/dL, where the guidelines' lines fall. A dashed circle means an approximate line.

Endocrine Society (2018)

Below 264 ng/dL (9.2 nmol/L), standardized assays

CUA (Canada, 2021)

Below 10 nmol/L (about 290 ng/dL)

AUA (US, 2018, reconfirmed 2024)

Below 300 ng/dL (10.4 nmol/L)

Endocrine Society statement (July 2026)

“Near 300 ng/dL”

EAU · ICSM · BSSM (Europe 2026 · international 2024 · UK 2023)

Below 12 nmol/L (about 350 ng/dL)

Every guideline also requires symptoms, and all but the CUA call for at least two morning tests; none diagnoses from a number alone.

Morning timing matters because testosterone is highest early in the day: in men aged 30 to 40 it was 20 to 25% lower at 4 pm than at 8 am. [55] The testosterone unit converter switches between ng/dL and nmol/L, and the TRT blood work guide explains when to draw each test on each form.

Who is TRT for, according to guidelines?

TRT is for men with symptoms of low testosterone whose level is low on at least two separate early-morning tests, after reversible causes have been looked for. Guidelines agree it is not for men with normal levels, and not something to screen every man for. [3], [4], [5]

How is low testosterone diagnosed?

Three things together: symptoms, a low number and a repeat test.

• Symptoms. The ones most closely tied to low testosterone are sexual: low desire, fewer morning erections and erectile problems. Tiredness and low mood are common but have many other causes. [24], [50]
• Two morning tests. US labels and the AUA require low results on at least two separate mornings before starting. The Endocrine Society also asks for fasting samples, and a free testosterone result when SHBG (the protein that carries testosterone in the blood) is unusual. [11], [3], [4]
• The cause. Guidelines then check LH and FSH, the pituitary signals, to tell primary hypogonadism (the testicles fail) from secondary hypogonadism (the brain's signal is too weak). The primary vs secondary hypogonadism guide explains why that matters for fertility and for stopping. [4], [5]

In the European Male Ageing Study, 11.8% of men aged 40 to 79 had the secondary pattern, mostly linked to obesity, and 2.0% the primary pattern, mostly linked to age. [56]

Should reversible causes be fixed first?

Yes, in every guideline. Obesity, opioid painkillers, corticosteroid medicines, sleep apnea, heavy alcohol use, acute illness, extreme exercise or dieting, and high prolactin can all lower testosterone, and the Canadian guideline asks for these to be managed and the level re-checked before starting. The Endocrine Society's 2026 statement calls weight loss the usual first step when overweight or obesity is the only cause. [53], [50], [5]

Lifestyle changes cannot fix some causes, such as testicular damage, Klinefelter syndrome (an extra X chromosome, about 1 in 650 men, most of them never diagnosed) or pituitary disease. These need their own medical assessment; for pituitary causes, other hormones can raise testosterone and restore fertility, which testosterone itself cannot. [57], [4], [5] See obesity-related hypogonadism and late-onset hypogonadism.

Do all men over 40 need TRT?

No. No guideline recommends testing or treating men just because of age. The Endocrine Society advises against routinely prescribing testosterone to all men 65 or older with a low level and offers it case by case to men with symptoms and consistently low morning tests. Its 2026 statement adds that diagnosis works the same way at any age. The 2014 EU-wide review concluded that raising testosterone in healthy older men is not an authorised use. [4], [50], [58]

Can TRT help if your testosterone is normal?

Not in the ways people hope. The European Association of Urology says not to use testosterone in men with normal levels, or to improve thinking, vitality or strength in ageing men. A 2024 Cochrane review of men with sexual problems who did not have diagnosed low testosterone found it probably has little to no effect on erections. [5], [59]

What should be discussed before starting?

• Fertility. Testosterone switches off sperm production, so the AUA says it should not be prescribed to men who are trying to conceive, and men who want children later should hear about the long-term effect first. [3] See TRT and fertility.
• Baseline checks. Hematocrit, and PSA in men over 40, before the first dose. [3], [4]
• What success would look like, and when to review. Several guidelines set a review point at 3 to 12 months (see how long a trial of TRT lasts).

The starting TRT guide walks through the first appointments and tests step by step.

How does TRT work?

TRT supplies testosterone from outside the body, and the brain responds by turning down its own signal to the testicles. That trade-off explains most of what TRT does, good and bad. [11], [60]

Normally the hypothalamus in the brain releases a hormone that tells the pituitary gland to send LH and FSH to the testicles. LH tells the Leydig cells to make testosterone, and FSH, with testosterone made inside the testicle, supports sperm production. When blood testosterone is high enough, the brain eases off. [11], [60]

TRT uses that feedback loop in reverse. Testosterone from outside tells the brain there is plenty, so LH and FSH fall and the testicles make less of their own. [11]

Why does TRT shrink the testicles and lower sperm counts?

Because sperm production needs far more testosterone inside the testicle than in the blood. In normal men, the level inside the testicle was about 40 to 100 times the blood level in two studies. When healthy men were given 200 mg of enanthate a week for 3 weeks in a research study, LH fell to 5% of its starting value and testosterone inside the testicle fell by 94%. In a small contraception study of enanthate combined with levonorgestrel (a progestin hormone), testosterone inside the testicle fell by 98% while blood testosterone stayed normal, and sperm counts fell from 65 to 1.3 million per mL. With less stimulation the testicles make fewer sperm, and labels report testicular shrinkage. [61], [62], [60], [34]

That is why TRT is not a fertility treatment, and why labels warn that reduced fertility on TRT may not fully reverse in some men. Medicines that keep the testicle working, such as hCG, are covered in the TRT and fertility guide. [11]

Why do men on TRT still need estrogen?

Because part of testosterone's effect comes from estradiol, the estrogen the body makes from it. In a trial in older men, testosterone gel improved spine bone density but anastrozole, which raised testosterone while blocking estrogen, did not. The AUA suggests measuring estradiol only when there are breast symptoms, and considers aromatase inhibitors only in specific cases. [63], [3] See estrogen on TRT.

What does the research show TRT can and cannot do?

In men with confirmed low testosterone, TRT reliably improves sex drive and sexual activity, bone density and anemia, with smaller effects on mood, erections and body composition. In the large trials it did not improve vitality, walking or thinking, although one TRAVERSE analysis found a small gain in self-reported energy. The best evidence comes from two large placebo-controlled programs: the Testosterone Trials (790 men aged 65 or older, 1 year of gel) and TRAVERSE (about 5,200 men aged 45 to 80 at high heart risk, gel for an average of 21.7 months). [6], [9], [7]

[6], [64], [65], [66], [7], [67], [68], [69], [10], [70], [71], [72], [8]

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What the large trials found TRT can and cannot do

Placebo-controlled trials and pooled analyses in men with low testosterone.

Improved

Sex drive and sexual activity

Testosterone Trials; TRAVERSE men with low libido: about 0.5 more sexual acts a day (questionnaire)

Spine bone density (CT scan)

Up 7.5% vs 0.8% in 1 year (Testosterone Trials, 211 men)

Unexplained anemia

Corrected in 58.3% vs 22.2% (Testosterone Trials)

Small or mixed

Erections

About 2 points in pooled trials; no gain in TRAVERSE men with low libido

Mood

Small improvement; no clear benefit in 49 men with persistent low-grade depression (TRAVERSE)

Body composition

About 1.6 kg less fat, 1.6 kg more lean mass (29 trials)

Diabetes

T4DM: 12% vs 21% with a lifestyle program; TRAVERSE: no significant prevention

Not improved

Energy (vitality)

No gain on the main measure (Testosterone Trials; 2026 review); one TRAVERSE analysis found a small self-reported gain

Walking

Main physical-function goal not met (Testosterone Trials)

Memory and thinking

Testosterone Trials (493 men); TEAAM (3 years)

Worse

Clinical fractures

3.50% vs 2.46% (TRAVERSE)

A summary of trial results, not a prediction for any one man. Heart rhythm, clot and kidney results are in the TRAVERSE figure.

Does TRT improve sex drive and erections?

Sex drive more than erections. In the Testosterone Trials, a year of gel improved sexual activity, desire and erectile function compared with placebo. In TRAVERSE, among 1,161 men with low libido, testosterone increased sexual activity by about half an act a day on the trial's questionnaire, which counted activity with or without a partner, and improved desire for up to 24 months, but did not improve erections. In pooled trials of men below 12 nmol/L, erectile scores rose by about 2 points, enough to matter for mild erectile problems. [6], [64], [65] See TRT and sexual health.

Does TRT help mood, energy or thinking?

Mood a little; energy and thinking not clearly.

• Mood. Depressive symptoms improved slightly in the Testosterone Trials and in a meta-analysis of 27 trials (1,890 men). In TRAVERSE, mood improved slightly overall, but the 49 men with persistent low-grade depression showed no clear benefit, too few to settle the question. The European Academy of Andrology advises against testosterone as the only treatment for depression. [6], [73], [66], [74]
• Energy. The Testosterone Trials found no improvement in vitality, and a September 2026 review of both big trial programs concluded that testosterone does not improve it. One TRAVERSE analysis found a small gain in self-reported energy, so TRT is not an established treatment for tiredness. [6], [7], [66]
• Thinking. A year of gel did not improve memory in 493 men with age-related memory problems, and 3 years of gel in the TEAAM trial did not improve any area of thinking tested. [67], [68]

See TRT and mental health.

Does TRT build muscle and burn fat?

Modestly. Across 29 trials in middle-aged and older men, testosterone reduced fat by about 1.6 kg and added about 1.6 kg of lean mass without changing body weight, and strength gains in older men were small on average. The extra lean mass was gone 6 months after stopping in frail older men, and guidelines advise against testosterone as a weight-loss treatment. [71], [75], [76], [5] See TRT, muscle and fat loss.

Does TRT strengthen bones?

It raises bone density, but in TRAVERSE it did not prevent fractures; fractures were more common. In 211 men in the Testosterone Trials, spine bone density measured by CT scan rose 7.5% on testosterone vs 0.8% on placebo in one year. Yet in TRAVERSE, clinical fractures occurred in 91 of 2,601 men on testosterone (3.50%) vs 64 of 2,603 on placebo (2.46%), and a 2026 meta-analysis also found more clinical fractures with testosterone (risk ratio 1.55), though not more hip or spine fractures. Nobody yet knows why. [69], [10], [77]

Does TRT prevent diabetes?

Not on its own. The two big trials studied different men and got different answers. In T4DM, 1,007 men aged 50 to 74 with a large waist, prediabetes or new diabetes and a testosterone level at or below 14 nmol/L but no known disease of the testicles or pituitary, all in a lifestyle program, had testosterone undecanoate injections or placebo for 2 years; diabetes at 2 years was 12% (55 of 443) vs 21% (87 of 413). TRAVERSE, using gel without a structured lifestyle program, found no significant slowing of progression to diabetes (for example 7.8% vs 10.7% at 12 months). [72], [8]

The American Diabetes Association's 2026 standards do not recommend testosterone to prevent diabetes, the Endocrine Society advises against it for blood-sugar control, and a 2026 review concluded that "TRT should not be regarded as an antidiabetic or lipid-lowering intervention." [78], [4], [79]

How long does TRT take to work?

Weeks for sex drive, months for most other changes. A review of treatment studies found sex drive improving from about 3 weeks, mood from 3 to 6 weeks, erections over up to 6 months, body composition from 12 to 16 weeks, and bone from 6 months onward; red blood cells rise within about 3 months and peak at 9 to 12 months. The Canadian guideline tells men to expect changes in libido and sexual function after 3 months or longer. [80], [53] See the TRT results timeline.

Does low testosterone shorten life?

Men with low natural testosterone die sooner on average in observational studies, but that does not show TRT lengthens life. A meta-analysis found the link, along with signs that low testosterone may mark poorer overall health rather than cause it. In TRAVERSE, deaths from any cause were similar: 144 of 2,596 men on testosterone vs 148 of 2,602 on placebo. [81], [9]

Is TRT safe?

For men with confirmed low testosterone who are monitored, TRT has well-understood risks, and the largest trial ruled out a large rise in its combined measure of heart attack, stroke and heart death over about two years of gel treatment. It is not risk-free: it raises red blood cells and blood pressure, switches off sperm production, and in TRAVERSE it increased atrial fibrillation, lung clots, kidney injury and fractures. Long-term safety beyond a few years, and on injections specifically, is still unknown. [9], [2], [10], [50]

Where did the heart-attack scare come from?

From one small trial and two records studies. In 2010, a gel trial in 209 men aged 65 and older with limited mobility and many health problems was stopped early after cardiovascular-related events in 23 men on testosterone vs 5 on placebo, out of 209 men split between the two groups; it was not designed to measure heart risk. A 2013 VA records study reported 3-year event rates of 25.7% with testosterone vs 19.9% without and was later corrected, and a 2014 claims study found heart attacks 1.36 times as common in the 90 days after a first prescription as in the year before. [82], [83], [84]

The FDA announced a review on January 31, 2014, while stating it had "not concluded" that testosterone raises heart risk, and an EU-wide review that year found no consistent evidence of higher heart risk. In March 2015 the FDA required labels to say benefit in age-related low testosterone is not established and called for a large safety trial, which became TRAVERSE. [85], [58], [13]

What did TRAVERSE show about the heart?

TRAVERSE randomized 5,204 men aged 45 to 80 with low testosterone (two fasting levels under 300 ng/dL), symptoms and existing heart disease or high heart risk to daily 1.62% testosterone gel or a placebo gel. Among the 2,596 men who used testosterone and the 2,602 who used placebo: [9], [86]

• Heart attack, stroke or heart death: 182 men (7.0%) vs 190 (7.3%); hazard ratio 0.96, with a 95% confidence interval of 0.78 to 1.17. That met the trial's safety margin, ruling out a large rise in risk. [9]
• Heart rhythm: atrial fibrillation 3.5% vs 2.4%; nonfatal rhythm problems needing treatment 5.2% vs 3.3%. [2]
• Clots: venous clots 1.7% vs 1.2%, including pulmonary embolism (a clot in the lungs) 0.9% vs 0.5%. [2]
• Kidneys: acute kidney injury 2.3% vs 1.5%. [2]
• Fractures: 3.50% vs 2.46%. [10]
• Blood pressure: systolic pressure rose 1.0 mm Hg on testosterone and fell 0.5 mm Hg on placebo by 36 months. [2]

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TRAVERSE: absolute results

Testosterone gel (2,596 men)Placebo gel (2,602 men)

Heart attack, stroke or heart death

Testosterone 7.0% vs placebo 7.3% (182 vs 190 men; hazard ratio 0.96, 95% CI 0.78–1.17; met the 1.5 safety margin)

Nonfatal rhythm problems needing treatment

Testosterone 5.2% vs placebo 3.3%

Atrial fibrillation

Testosterone 3.5% vs placebo 2.4%

Clinical fracture

Testosterone 3.5% vs placebo 2.5% (91 of 2,601 vs 64 of 2,603 in the full analysis set)

Acute kidney injury

Testosterone 2.3% vs placebo 1.5%

Venous clots (all)

Testosterone 1.7% vs placebo 1.2%

Pulmonary embolism

Testosterone 0.9% vs placebo 0.5%

About 5,200 men aged 45–80 at high heart risk; daily gel; mean treatment 21.7 months; about 61% stopped their study gel. Not a trial of injections.

Its limits matter. TRAVERSE tested only a daily gel, the average man used it for 21.7 months, about 61% stopped their study gel early, and it enrolled men at high heart risk. It did not test injections, which the Endocrine Society says raise red blood cells more often than gels. [9], [2], [4] On February 28, 2025, the FDA told makers to add TRAVERSE's results to all testosterone labels, remove the boxed-warning language about heart risk and add blood-pressure warnings. Most brand labels now carry TRAVERSE, but the cypionate and enanthate vial labels and the pellet label still say no long-term heart safety trial has been done (checked September 2026). [13], [28]

Pooled trials point the same way: a 2025 meta-analysis of 23 trials lasting at least a year found no increase in death, heart attack or stroke but about 50% more heart-rhythm problems (risk ratio 1.53), and a 2026 meta-analysis of 41 trials (11,161 men) found no increase in major heart events. [87], [88]

Is the heart question settled?

Medical societies read the same evidence differently:

Where the sources disagree. The Androgen Society, a medical society focused on testosterone, wrote in 2024 that it is "conclusively determined" that testosterone does not raise heart attack, stroke or heart death. The Endocrine Society's July 2026 statement agrees there was no meaningful rise in heart attack or stroke over 1 to 4 years, but points to a roughly 50% relative rise in pulmonary embolism and more fractures, says long-term safety, including for the prostate, is not established, and calls for a larger long-term study. [89], [50]

A second argument is about dose. One reviewer argues that TRAVERSE men were undertreated, saying the average increase was "only 9.3 to 12.9 nmol/L"; the label summary of the same trial reports average testosterone rising from 220 to about 440 ng/dL (about 15.3 nmol/L) at 12 months. [90], [2] The TRT and heart health guide covers the trial in full.

Does TRT cause prostate cancer?

The trials so far do not show it, but long-term data are missing and labels still forbid testosterone for men with prostate cancer. The fear goes back to Charles Huggins's 1941 research showing that prostate cancer depends on hormones; a later review notes that its finding against giving testosterone rested on a single patient. [91]

• The saturation idea. A later theory holds that prostate tissue stops responding to extra testosterone once its receptors fill up "well below the physiologic range". It remains a hypothesis, and a 2020 review urged caution in applying it. [92], [91]
• TRAVERSE, which excluded men with PSA above 3.0 ng/mL, found high-grade prostate cancer in 5 of 2,596 men on testosterone (0.19%) vs 3 of 2,602 on placebo (0.12%) (hazard ratio 1.62, 95% confidence interval 0.39 to 6.77). With so few cases, this neither shows a difference nor proves the risks are the same. PSA rose about 0.15 ng/mL more than on placebo at 12 months. [86]
• A 2026 trial of cypionate in 136 men treated surgically for low-grade prostate cancer found no PSA recurrence over 12 weeks, too short to judge long-term cancer safety. [93]

US labels contraindicate testosterone in known or suspected prostate cancer. In June 2026 the FDA asked for that to be narrowed to metastatic prostate cancer only; that change was still a request in September 2026. [28], [21] See TRT and the prostate.

What does TRT do to red blood cells?

It raises them. In a review of placebo-controlled trials in men aged 45 and older, testosterone nearly quadrupled the odds of a hematocrit above 50%. [94] In pooled trials, cypionate or enanthate injections raised hematocrit by about 4 points and gels by about 3, although that analysis could not confirm a difference between the two; in the T4DM trial of long-acting injections, 22% of men on testosterone (106 of 491) went above 54% vs 1% on placebo (6 of 484). Most guidelines act at 54%. [49], [72], [3] See hematocrit on TRT.

What does TRT do to fertility?

It lowers sperm production, often to zero: in a contraception trial, 200 mg of enanthate a week left 65% of healthy men with no sperm within 6 months. In an analysis of such trials, sperm counts were estimated to return to a fertile level (20 million per mL) in 67% of men within 6 months of stopping and 100% within 24 months, but men on TRT are older and have their own reasons for low testosterone, and labels warn that reduced fertility may be irreversible in some. [95], [96], [11] Guidelines say not to use testosterone in men trying to conceive. [3], [5] See TRT and fertility.

What other side effects do labels list?

The labels list acne, oily skin, male-pattern hair loss, breast enlargement (gynecomastia), fluid retention, changes in sex drive, headache, anxiety, depression, prolonged erections, a rise in red blood cells and, for injections, pain at the injection site. Labels also report testicular shrinkage. [28], [34]

• Blood pressure. FDA studies confirmed that all testosterone products can raise blood pressure, and labels advise against use with uncontrolled high blood pressure. [13]
• Sleep apnea. Labels warn testosterone may worsen sleep apnea, especially with obesity or lung disease; in T4DM, new sleep apnea diagnoses were more common on testosterone (3.0% vs 0.4%). [34], [97]
• Hair loss. No controlled study has measured how much replacement-dose TRT speeds male-pattern hair loss; the label lists it among reported reactions. [28]
• Transfer. Gels can pass testosterone to children or partners through skin contact, which is why US gels carry a boxed warning. [34]
• Aveed injections. Oil can reach the lungs, or a severe allergic reaction can happen, during or just after an injection, so the US label requires 30 minutes of observation in the clinic after every dose. [32]
• Mood. The Xyosted label warns about depression and suicidal thoughts: across its two trials (one lasting a year, one 6 months), 2 of 283 men stopped because of depression and 2 others attempted suicide, one fatally. New or worsening low mood needs prompt medical help. [11]

The TRT side effects guide covers each one, with what helps.

Will TRT make me aggressive?

At replacement doses, the evidence says no. A 2020 meta-analysis found that giving testosterone had a small effect on aggression that was not statistically significant. In an older study of 51 men with low testosterone restarting replacement, anger and irritability fell compared with their untreated state, although there was no placebo group. [98], [99]

Very high doses are different: in a trial of research doses far above replacement, 12% of healthy men became mildly and 4% markedly hypomanic (abnormally elevated and energetic), and labels link steroid misuse with hostility and aggression. [100], [28]

Who should be especially cautious?

• Men who want children now or soon. Testosterone suppresses sperm production; guidelines advise against it for men trying to conceive. [3]
• Men with prostate or breast cancer. Contraindicated on current US labels and in the Endocrine Society guideline; the European guideline lists locally advanced or metastatic prostate cancer and male breast cancer. [28], [4], [5]
• A PSA above 4 ng/mL (above 3 ng/mL at high prostate-cancer risk), a prostate nodule or severe urinary symptoms, until a urologist has checked. [4]
• A high hematocrit, a history of blood clots or an inherited clotting disorder. [4], [14]
• Untreated severe sleep apnea, uncontrolled heart failure, or a heart attack or stroke in the past 3 to 6 months. [4], [3]
• Serious heart, liver or kidney disease, because of fluid retention. [101]
• Women and children. Testosterone is contraindicated in pregnancy. These guides are for men; see testosterone therapy for women. In teenagers it can close growth plates early, so any use belongs in specialist care. [28]
• Drug-tested athletes. Banned at all times (see sport). [19]
• People taking other medicines (see the next question).

Which medicines interact with testosterone?

Labels name three interactions, the Xyosted and oral capsule labels add a fourth, and two other medicine groups matter for men on TRT:

• Insulin and other diabetes medicines. Testosterone can lower blood sugar and so the dose of diabetes medicine needed. [28]
• Blood thinners. Labels report bleeding in people also taking oral anticoagulants, and the Azmiro label advises frequent clotting tests (INR), especially when testosterone starts or stops. [28], [29]
• Corticosteroids. Together they can increase fluid retention. [101]
• Medicines that raise blood pressure. The Xyosted and oral capsule labels warn that some prescription medicines, and some over-the-counter pain and cold medicines, can add to testosterone's rise in blood pressure. [11], [2]
• SGLT2 inhibitors (diabetes medicines such as empagliflozin and dapagliflozin). In a study of 53,971 US veterans with diabetes, 756 (1.4%) developed a hematocrit above 54% within a year, and men taking an SGLT2 inhibitor with testosterone had about 2.5 times the odds of men on testosterone alone, and an EU safety review in September 2025 recommended adding this warning to testosterone labels. [102], [103]
• Opioid painkillers can themselves lower testosterone. Their labels note androgen deficiency with long-term use, and a 2020 meta-analysis found low testosterone in 63% of men using opioids. [104], [105]

Current US labels for GLP-1 weight-loss medicines such as semaglutide (Wegovy) and tirzepatide (Zepbound) list no interaction with testosterone, though they advise care with medicines taken by mouth, which includes oral testosterone. [106], [107] See TRT with GLP-1 medicines. Bring a complete list of what you take, including supplements, to a pharmacist or prescriber. Checked September 2026.

Is TRT legal, and is it allowed in sport?

Checked September 2026. Rules differ by country and change often.

TRT is legal with a prescription in every country covered here, and testosterone is a controlled medicine in each of them. It is not on the UN's list of internationally controlled psychotropic substances, so each country sets its own rules. [108]

United States. Testosterone and its esters are Schedule III controlled substances, and no proposal to deschedule them has been published. [15] The key steps:

• 2015 and 2016. Labels were required to say that benefit in age-related low testosterone is not established, and since 2016 they carry warnings on abuse and dependence. [13], [109]
• February 28, 2025. The FDA told makers to add TRAVERSE results and blood-pressure warnings to all labels and to remove the boxed-warning language about heart risk; the vial and pellet labels still lack the TRAVERSE results (checked September 2026). In July 2025 the blood-pressure boxed warnings on Xyosted, Jatenzo, Tlando and Kyzatrex were also removed, so the only boxed warnings left are on Aveed (oil reaching the lungs and allergic reactions) and on gels and solutions (transfer to others). [13], [110], [32]
• December 2025 and April 2026. The FDA held an expert panel on TRT for men, then invited makers to apply for a new use in low libido in men with low testosterone of unknown cause. That is an invitation; no such use is approved. [111], [112]
• June 18, 2026. The Department of Health and Human Services (HHS) announced that the FDA is requesting label changes: removing the age-related limitation, contraindicating testosterone only in metastatic prostate cancer, and revising the prostate-enlargement warning. These are requests; the newest labels still carry the old wording. [21], [20]
• Telehealth. Temporary rules let clinicians prescribe controlled medicines such as testosterone without an in-person visit through December 31, 2026. A permanent Drug Enforcement Administration (DEA) special-registration rule has been under White House review since August 25, 2026 and is not yet published. [113], [114]

United Kingdom. Testosterone is a Class C controlled drug in Schedule 4 Part II, prescription-only. Possessing it is not an offence, but supplying it without authority is. [16], [115]

Canada. Testosterone is a Schedule IV controlled substance and prescription-only. [17]

Australia. Testosterone is a Schedule 4 (prescription-only) medicine with extra controls on possession. [18]

European Union. Rules are national. The 2014 EU-wide review requires low testosterone to be confirmed by signs, symptoms and lab tests before treatment. [58] See the country guides for the US, the UK, Canada, Australia and Europe, which cover coverage and costs.

A "research use only" label on a vial does not make it legal, tested or the same as a licensed medicine.

Is testosterone banned in sport?

Yes. The World Anti-Doping Agency (WADA) prohibits testosterone at all times, and its 2027 list keeps the ban. An athlete with a medical need can apply for a therapeutic use exemption, which for adult men WADA grants only when low testosterone has an organic cause, such as a testicular or pituitary disorder, and not for age, obesity or earlier steroid use. Its guidance treats delayed puberty in teenagers as a separate specialist case. [19], [116], [117]

Is TRT for life, and can you stop?

Often, but not always. TRT replaces testosterone rather than fixing the cause, so levels fall again when it stops. Whether it is lifelong depends on that cause: permanent damage to the testicles or pituitary usually means lifelong treatment, while low testosterone driven by weight, medicines or illness can sometimes recover. [54], [118]

How long should a first trial of TRT last?

Guidelines disagree. Several set a review point and suggest stopping if symptoms have not improved despite a normal testosterone level: the Canadian guideline after about 3 months, the AUA at 3 to 6 months, the BSSM at 6 months and the VA at 6 to 12 months. The UK Society for Endocrinology rejects the idea of a time-limited trial and expects lifelong treatment once the diagnosis is confirmed. [53], [3], [52], [14], [54]

What happens if you stop TRT?

Testosterone falls, the brain's signals slowly restart, and symptoms of low testosterone can return in the meantime.

• Hormones recover slowly. After men stopped 2 years of testosterone undecanoate injections in the T4DM trial, their own LH and FSH recovered gradually over 12 months, and full recovery may take longer than a year after the last injection. [119]
• Some come back to it. About five years after T4DM ended, 6% of former testosterone users had restarted testosterone vs 2.8% of former placebo users. [97]
• Benefits fade. Gains in lean mass and symptoms were gone 6 months after stopping in frail older men. [76]
• No taper is required by the Canadian guideline. [53]

No study has followed natural recovery after stopping in men with permanent hypogonadism, where the testicles or pituitary are damaged. The stopping TRT guide covers recovery, fertility and restart medicines.

Is TRT the same as steroids?

No. Both use testosterone, but TRT aims to restore a normal level in a man whose level is low, with regular blood tests. Non-medical steroid use aims for levels well above normal, usually with several drugs at once. The Endocrine Society notes that most users are not competitive athletes but recreational weightlifters, and that they "frequently consume highly supraphysiologic doses" (far above the body's natural range). [120]

Non-medical steroid use is common: a meta-analysis of 187 studies estimated that 6.4% of men worldwide have used anabolic steroids at some point. [121]

What separates a replacement dose from steroid use?

The level it produces and the monitoring around it. In a research study that switched off healthy young men's own testosterone and gave rising weekly doses, higher doses added more lean mass but also raised hemoglobin and lowered HDL ("good") cholesterol, while sexual function, mood and a test of spatial thinking did not change at any dose. US labels state that testosterone "has not been shown to be safe and effective for the enhancement of athletic performance". [122], [28]

What happens to natural testosterone after steroids?

Recovery varies. In a study following 100 amateur athletes through one cycle, average testosterone was back to its starting level 3 months after the cycle ended, but 11% of those assessed still had low testosterone a year after the cycle began, and sperm took longer to recover. Smaller or selected samples of former and longer-term users find more lasting problems: among 33 former users about 2.5 years after stopping, 27% still had low testosterone. In a clinic of 641 men tested once, anywhere from a week to 36 months after stopping, only 48.2% had fully normal reproductive hormones. Neither is a recovery rate for all steroid users. [123], [124], [125] The TRT vs steroids guide explains the terms people use and the risks.

Can you raise testosterone without TRT?

Sometimes, when the cause is reversible, and weight loss has the best evidence. Supplements sold as "testosterone boosters" mostly do not.

• Weight loss. In a meta-analysis, testosterone rose about 2.9 nmol/L after a low-calorie diet and about 8.7 nmol/L after bariatric surgery, with bigger losses giving bigger rises. The European Association of Urology describes diet-related gains as more modest, about 1 to 2 nmol/L, and notes that most lost weight is regained within three years. [126], [5]
• GLP-1 medicines. In small, short studies of men with obesity-related low testosterone, GLP-1 drugs and tirzepatide raised total testosterone by about 2.5 to 5.2 nmol/L. [127]
• Sleep. One week of 5-hour nights lowered daytime testosterone by 10 to 15% in 10 healthy young men. [128]
• Exercise. Training did not change resting testosterone in inactive men with normal levels, in a meta-analysis of 11 trials, though it helps health and body composition. [129]
• Sleep apnea treatment. CPAP (a mask that keeps the airway open during sleep) did not significantly raise testosterone in a meta-analysis; obesity rather than the apnea itself seems to set the level. [130]
• "Testosterone boosters." In a review of 50 products, only 24.8% of ingredients had any data showing a rise in testosterone, 10.1% had data suggesting a fall, and 13 products exceeded safe upper limits for zinc, niacin or magnesium. The Canadian guideline says boosters cannot be recommended, and the FDA does not approve supplements for safety or effectiveness. [131], [53], [132]

Lifestyle cannot restore testosterone when the testicles or pituitary are damaged. The increase testosterone naturally guide covers each option in detail.

How do you find good TRT care?

Look for care that follows the guidelines: symptoms plus repeated morning tests before starting, a search for the cause, a fertility conversation, and regular checks of testosterone, hematocrit and PSA. Studies of online advertising and direct-to-consumer services show why this is worth checking. [3], [4]

Why do doctors worry about over-prescribing?

Because prescribing has swung widely, and not always with testing:

• Rise. Among US insured men aged 40 and older, testosterone use more than tripled from 0.81% in 2001 to 2.91% in 2011, and only 74.72% of new users had a testosterone test in the year before. In a second study, 40.2% of US and 53.8% of UK starters had no test recorded in the 180 days before starting. [133], [134]
• Fall. After the 2013 to 2014 heart reports and FDA action, use among US insured men aged 30 and older fell from 3.20% in 2013 to 1.67% in 2016. [135]
• Rise again. In US states that shared prescription-monitoring data, the number of people filling testosterone rose 27% from 2018 to 2022, with the largest rises at ages 35 to 54. In Australia, prescriptions were back to 98% of their 2014 peak by 2023. [136], [137]

No verified count exists of how many US men are on TRT today.

What do online TRT services get wrong?

In a 2022 "secret shopper" study, a man with normal testosterone who wanted children in the future approached 7 US direct-to-consumer platforms: 6 offered him testosterone, only 1 of the 7 asked about recent heart events and only 1 about future fertility, and 5 of the 6 did not discuss the risk of high red blood cells. [138] A 2026 analysis of 253 clinic websites in several languages found that 86.2% made at least one claim that disagreed with international guidelines, 9.9% offered testosterone to men with levels above 12 nmol/L, 20.6% claimed it lowers heart risk, and only 28.5% mentioned that it may impair fertility. [139]

The AUA also advises commercially made testosterone over compounded products when possible. [3] Good questions for any prescriber: Which guideline do you follow? How will you confirm the diagnosis and look for a cause? What happens if I want children? How often will you check hematocrit and PSA, and what will you do if they rise?

What do people on TRT report?

Public forums are full of men weighing whether to start, men who say TRT changed their lives, and men who stopped. The threads below are public Reddit discussions from the past year, read with their replies and described without identifying anyone. They show what people experience, not how often it happens.

What do positive reports look like?

Better sex drive, energy, mood and sleep, usually over months. A man in his 30s with a pretreatment level he gave as 200 described, after a year on 100 mg a week, more energy, better sexual function and mood, and muscle gain alongside new weight training, while noting smaller testicles and more body hair. [140] A man in his 30s with 15 years of insomnia began feeling sleepy at a normal bedtime within days of starting injections and still did at 6 months, though replies described sleep getting worse for others. [141] Some of the clearest responses come from men with very low levels and a known cause: one man with hypogonadotropic hypogonadism (a weak signal from the brain) and a level of 0.87 nmol/L felt no better on hCG alone, then reported feeling much better about seven weeks after starting testosterone. [142]

Does everyone feel better?

No, and the reason often turns out to be something else. A man in his 20s with levels of 305 and 375 had no relief after 10 months of TRT; a sleep study then found moderate sleep apnea, and after CPAP he reported sleeping well and, months later, feeling well. [143] A man in his 40s who had planned to start with a level of 340 treated low vitamin D and ferritin (stored iron) and changed his sleep timing instead; 14 weeks later he had more energy and a level of 510, with TRT on hold. [144] Others raised their testosterone, through weight loss or enclomiphene, without the symptom they hoped to fix changing. [145], [146]

Men who start with normal levels often describe regret. A man in his 20s who started at 550 ng/dL found his physique and focus largely unchanged after 6 months while he had hair shedding, worse skin and breast tissue changes (he had also used steroids before and took a hair-loss medicine). Another in his 20s, who started through an online clinic after seeing influencers' posts, on 250 mg a week (more than guideline starting doses), described modest early benefits, worse sleep, testicular shrinkage and a cost he could no longer afford. [147], [148] Replies regularly push back on starting from one result or from "normal" labs, and ask about sleep, weight, alcohol, medicines and mental health first. [149], [150]

What unwanted effects come up?

• Heart rhythm. A man in his 30s whose level was 565 before starting was diagnosed with atrial fibrillation a few months in and stopped; the post does not establish the cause. [151]
• Blood and iron. One man described six good months followed by high hematocrit, low ferritin, anxiety, hair loss and tinnitus, which a lower dose did not fix; he also reported an iron disorder, and stopped after about a year. [152]
• Blood pressure and headaches. A man in his 30s who felt markedly better on enanthate stopped because of high blood pressure and painful headaches during exercise. [153]

Is the "lifelong commitment" fear justified?

It is the most common worry before starting. A man in his 50s with levels of 204 to 327 ng/dL asked how others "crossed the bridge"; replies described injections as manageable but disagreed about whether treatment must be lifelong. [154] Stopping stories point both ways: one man stopped after about 2 years because he wanted children and felt worse off treatment than before he started, while another felt steadier after stopping but had also taken enclomiphene, a weight-loss medicine, a peptide and several supplements. [155], [156]

Where does TRT end and steroid use begin?

In many threads, not where posters draw it. When one man described alternating his usual dose with far higher "cycle" doses and calling it all TRT, replies strongly disputed the label, and a 19-year-old who felt great on a steroid cycle met replies disputing that a cycle predicts what replacement feels like. [157], [158]

How can you judge a TRT story?

Ask: What was the level before starting, on how many morning tests? Was a cause looked for? What was the dose, in mg per week, and was it prescribed? When was blood drawn relative to the last dose? What else changed at the same time, such as weight, sleep, alcohol, other hormones, weight-loss medicines or training? And what did the poster report months later?

These selected discussions show what people experience and the questions research has not answered. They are not a survey of all men on TRT, a success rate or a substitute for the trials above.

What should you track on TRT?

Guidelines check testosterone and hematocrit before starting, at 3 to 6 months, at 12 months and then yearly, plus PSA, blood pressure and how you feel; some product labels ask for hematocrit more often. Use this summary to prepare questions for your prescriber; it is not a personal testing plan. [4]

[4], [3], [5], [35], [13], [34], [11], [41], [2], [12]

For every testosterone result, note the date and time of your last dose. On injections, a level drawn near the peak and one drawn near the trough can differ a lot, and guidelines time the draw differently for each form. The TRT blood work guide covers timing, and the testosterone level visualizer shows how injection frequency changes the peaks and troughs. [4]

Common questions about TRT

Is TRT worth it?

For men with symptoms and clearly low testosterone on repeated tests, trials show real gains in sex drive, sexual activity, bone density and anemia. For men with normal or borderline levels, the evidence of benefit is weak, and the costs are real: regular blood tests, lower fertility and often long-term treatment. Guidelines suggest reviewing whether it helped after about 3 to 12 months. [7], [5], [3] See what the research shows.

What is a normal testosterone level for a man?

There is no single number, because labs and guidelines differ. The Endocrine Society uses 264 ng/dL (9.2 nmol/L) as the lower limit of normal with standardized assays, the AUA uses 300 ng/dL, and European guidelines 12 nmol/L (about 350 ng/dL). A result only means something with symptoms and a repeat morning test. [4], [3], [5] See the key numbers.

Does TRT shrink your testicles?

It can. Testosterone from outside switches off LH, the signal that keeps the testicles working, and labels report testicular shrinkage. Medicines such as hCG are sometimes added, mainly to protect fertility. In contraception trials, sperm counts were estimated to return to a fertile level within 2 years of stopping, but that does not guarantee recovery after TRT, and labels warn it may not fully recover in some men. [60], [34], [3], [96], [11] See how TRT works.

Does TRT cause hair loss?

It may, but no controlled study has measured how much replacement-dose TRT speeds male-pattern hair loss. Labels list male-pattern baldness among reported androgen side effects, and it comes up often in forum accounts. [28], [159] See the TRT side effects guide.

Can you start TRT in your 20s?

Yes, when low testosterone has a clear cause such as testicular damage or pituitary disease. For young men with borderline results, guidelines ask for repeat morning tests and a search for reversible causes first, and advise against testosterone for men trying to conceive. [3], [53] See who TRT is for.

Which is better: injections, gel or pills?

None is best for everyone. Injections mean a shot every week to few weeks and, according to the Endocrine Society, raise red blood cells more often than gels; gels are applied daily and can transfer to others by skin contact; oral capsules avoid needles but are taken twice daily with food. No trial ranks the forms on long-term outcomes. [4], [34], [41] See the key numbers.

Glossary

Plain explanations of the medical, lab and research terms used in this guide. Underlined terms in the text link here.

Anabolic steroid

Testosterone or a man-made drug related to it, used to build muscle. The term usually means non-medical use at doses far above the body's natural range.

Aromatase inhibitor

A medicine, such as anastrozole, that blocks the enzyme that turns testosterone into estradiol.

Azoospermia

No sperm at all in a semen sample.

Cohort study (records study)

A study that follows a group of people, or looks back at their records, without assigning treatments. It can show links but not prove that one thing caused another.

Controlled trial

A study that compares people who receive a treatment with a similar group who do not, often receiving a placebo instead. Randomly assigning people to each group makes the comparison fairer.

Estradiol

The main form of estrogen. In men it is made mostly from testosterone, so it rises when testosterone rises, and men need it for healthy bones.

Ester

A chemical tail joined to testosterone that makes it dissolve in oil and release slowly after injection. The body removes the tail to free testosterone. Cypionate, enanthate and undecanoate are esters.

Free testosterone

The small share of testosterone in the blood that is not bound to proteins and can act on tissues. It is measured or calculated when SHBG is unusual.

FSH (follicle-stimulating hormone)

A pituitary hormone that acts on the cells supporting sperm production. Testosterone therapy lowers it.

Clinical guideline

Recommendations written by a medical society or health system, based on its review of the evidence and expert judgment. Different guidelines can reach different conclusions.

Gynecomastia

Growth of breast tissue in men, often tender at first. It is linked to a higher estrogen-to-testosterone balance.

Hazard ratio

A measure comparing how often an event happens over time in two groups. A hazard ratio of 1 means no difference; 0.96 means about 4% lower in the first group.

Hematocrit

The share of the blood made up of red blood cells. Testosterone raises it, and most guidelines act when it reaches about 54%.

Secondary hypogonadism (hypogonadotropic hypogonadism)

Low testosterone because the brain and pituitary send too little LH and FSH to the testicles. It can be present from birth or start later, for example with obesity, opioids or pituitary disease.

Hypogonadism

Low testosterone caused by a problem in the testicles or in the brain and pituitary signals that control them, confirmed with symptoms and repeated morning blood tests.

Intramuscular (IM)

Injected into a muscle. Most testosterone cypionate and enanthate is given this way.

Klinefelter syndrome

A genetic condition in which a male has an extra X chromosome (47,XXY). It causes primary hypogonadism and affects about 1 in 650 males.

Product label (prescribing information)

The official document approved by a medicines regulator for a product, describing its approved uses, doses, warnings and monitoring. In the UK it is called the summary of product characteristics.

Leydig cells

Cells in the spaces between the testicle's tubules that make testosterone when LH reaches them.

LH (luteinizing hormone)

A pituitary hormone that tells the testicles to make testosterone. Testosterone therapy switches it off.

MACE (major adverse cardiovascular events)

A combined measure used in heart-safety trials. In TRAVERSE it meant heart attack, stroke or death from heart disease.

Meta-analysis and systematic review

A systematic review gathers all studies on a question in a planned way. A meta-analysis combines their results statistically.

Odds ratio

A measure comparing the odds of an outcome in two groups. An odds ratio of 2 means roughly twice the odds; 1 means no difference.

Placebo

A dummy treatment with no active ingredient, used as a comparison in studies.

Primary hypogonadism

Low testosterone because the testicles themselves do not work well, even though the pituitary sends plenty of LH and FSH.

PSA (prostate-specific antigen)

A blood test for a protein made by the prostate. It rises slightly on testosterone and is used to decide whether prostate checks are needed.

SHBG (sex hormone-binding globulin)

A blood protein that carries testosterone. Testosterone bound to it is not immediately available to tissues, so SHBG affects how much free testosterone there is.

Obstructive sleep apnea

Repeated blocking of the airway during sleep, causing pauses in breathing and drops in oxygen. Loud snoring and daytime sleepiness are common signs.

Subcutaneous (SC)

Injected into the fatty layer just under the skin. Xyosted is given this way.

Supraphysiologic

Above the range the body makes naturally. Steroid cycles use supraphysiologic doses; TRT aims for the normal range.

Transdermal

Absorbed through the skin, as with testosterone gels, creams and patches.

Trough level

The lowest level of a medicine in the blood, just before the next dose.

TRT (testosterone replacement therapy)

Prescribed testosterone, by injection, gel or other forms, for men with low testosterone. It switches off the brain's LH and FSH signals.

WADA

The World Anti-Doping Agency, which publishes the list of substances banned in sport. Testosterone is banned at all times.

How this guide was researched

This guide is built from a thorough review of the sources cited throughout it: clinical guidelines from the United States, Canada, the United Kingdom, Europe and international bodies, current product labels, the large testosterone trials and their follow-up studies, meta-analyses, studies of prescribing and online care, and regulatory records. We also reviewed public online forums where men describe their own experience of starting, living on and stopping TRT.

The guide cites 159 sources, including 47 original studies in people, 11 clinical guidelines and position statements, 25 product labels and 20 public community discussions. Each type of source answers a different question. Guidelines and labels show what clinicians are told to do. Trials and studies show what was measured. Personal accounts show what individual people experienced. Every numbered citation links to its entry below, labeled by source type.

How this guide was made

Research and drafting were AI-assisted. Every cited source was checked against its original text (abstract, full text or official page), and the guide was reviewed and edited by Doserly before publication. It has not had an independent clinical review, and Doserly does not currently have medical reviewers. Doserly makes a medication and health-tracking app and runs Doserly Academy, both of which are promoted in this guide. Read our editorial policy for how guides are researched, updated and corrected.

This guide is for educational purposes. It summarizes what the reviewed sources report so the research is easier to understand; it is not medical advice. For a deeper dive, or to check any point for yourself, go straight to the cited sources.

Explore the sources