TRT Side Effects: The Definitive Guide

What are the side effects of TRT?

TRT side effects are the unwanted effects of prescribed testosterone at replacement doses, meaning doses meant to bring a low level back into the normal range. Most are mild, and most follow from what testosterone normally does in the body: it makes the skin's oil glands more active, pushes the bone marrow to make more red blood cells, tells the brain to turn down the body's own testosterone and sperm production, and helps the body hold on to salt and water. [1], [6], [15], [16]

It helps to sort them into three groups:

• Changes you may not feel. Blood tests pick these up: a rise in hematocrit (the share of blood made of red cells), a small rise in PSA, a small fall in HDL cholesterol and, if tested, fewer sperm. [17], [18], [6]
• Things you may notice. Acne and oily skin, sore or tender nipples, swelling, smaller testicles, changes in sleep or mood, headaches, and reactions where you inject or apply the medicine. [12], [19], [6]
• Rare but serious. Blood clots, a severe cough or allergic reaction after an undecanoate injection, gel passing to a child or partner by skin contact, and depression or thoughts of suicide. [8], [11], [20], [6]

Much of what you read online about testosterone side effects comes from people taking several times a replacement dose outside medical care. Those amounts are not TRT and carry different risks; the TRT vs steroids guide explains the difference. [12]

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Which side effects are clearly linked to testosterone?

At replacement doses. The groups show how clear the link is, not how often each effect happens.

Clear link

Evidence of a link; more common

• Rise in red blood cells (hematocrit)
• Acne and oily skin
• Lower sperm production

Weaker or less common

Weak evidence of a link, or less common

• Breast enlargement (gynecomastia)
• Male-pattern balding, often familial
• New or worse sleep apnea
• Weight gain †
• Swings in mood, libido or hot flushes with stop-start treatment †

Depends on the form

Tied to how testosterone is given

• Injections: pain at the site, cough right after the injection, mood or libido swings
• Gels and solutions: skin irritation, transfer to others
• Patches: skin reactions
• Nasal gel: nasal symptoms

† Listed only by the Endocrine Society of Australia. Fluid retention and swelling can occur with any form. Grouping from the Endocrine Society 2018 guideline and the Endocrine Society of Australia 2016 position statement.

TRT side effects: the key numbers

This table shows what each major clinical guideline names as side effects, the numbers that trigger action, and how often they are checked. The numbers are what each document says, checked in September 2026.

[21], [1], [22], [23], [10], [24], [25], [2], [26], [6], [27]

Most guidelines act at a hematocrit of about 54%, and four use a PSA rise of more than 1.4 ng/mL. The Endocrine Society, EAA and VA refer to urology for a rise that size in the first year (the Endocrine Society asks for it to be confirmed); the BSSM applies it to any one-year period. The exceptions on hematocrit are the VA (adjust above 51%), the Society for Endocrinology (above 50%) and the CUA (55%). For symptoms such as acne, breast tenderness or mood changes, no guideline sets a number; they ask clinicians to review side effects at every visit and adjust. [1], [24], [26], [10], [25], [23]

Where do guidelines disagree?

On sleep apnea. The Endocrine Society calls the link weak but lists untreated severe sleep apnea as a reason not to start, and the US labels warn that testosterone may make sleep apnea worse, especially with obesity or chronic lung disease. The European urology guideline says there is no evidence that testosterone causes or worsens it, but its evidence summary covers mild or moderate sleep apnea and severe sleep apnea treated with CPAP, not untreated severe sleep apnea. The trials behind both views are covered in the sleep apnea question. [1], [6], [22]

How often did side effects appear in the product trials?

Each US label reports the side effects seen in its own trials. The numbers show what men on each product noticed, but they cannot be compared across products: the trials differed in length, men and methods, and most had no placebo group.

[20], [19], [28], [27], [6], [11], [9], [8], [29], [30], [31]

Only the AndroGel 1.62% and Testim trials had a placebo group, which is why the pooled trial reviews in the research section say more about what testosterone itself causes.

How do the units work?

Hematocrit is a percentage (54%) or a fraction (0.54 L/L). PSA is in ng/mL. Estradiol is in pg/mL in the US and pmol/L elsewhere: 40 pg/mL is about 147 pmol/L. The testosterone unit converter switches testosterone between ng/dL and nmol/L. [21]

Why do side effects happen?

Most side effects are testosterone doing its normal jobs a little too much, in the wrong place, or on an uneven schedule. These mechanisms are measured in people. [1]

• Oil glands. Testosterone makes the skin's oil glands produce more sebum, the oily substance that can block pores and feed acne. In people starting testosterone, sebum production rose; in a research study of healthy men given graded doses, forehead sebum rose with the dose. [15], [32]
• It is not all DHT. The skin turns some testosterone into DHT (dihydrotestosterone), a stronger androgen. But in that same study, blocking DHT with dutasteride did not change sebum, acne or hematocrit, so "it's all DHT" is too simple. [33], [32]
• Estradiol. The body turns some testosterone into estradiol, and breast tissue responds to it. Injections every 2 weeks produced above-normal testosterone and estradiol for several days after each shot. The estrogen on TRT guide explains the balance. [34]
• Salt and water. Testosterone increases the water held outside the body's cells, measured directly in men with pituitary disease, and the labels say it "may promote retention of sodium and water". [16], [35]
• Testicles and sperm. Testosterone from outside tells the pituitary gland to stop sending its two signals to the testicles, LH and FSH. In a 3-week research study, testosterone inside the testicles fell by 94%, and in a contraceptive study the testicles shrank by about a fifth in 4 months. [36], [37]
• Red blood cells. The hematocrit guide explains how testosterone raises them. [17]
• Peaks and troughs. Injections make levels rise and fall across each interval. In one small comparison in men with HIV and low testosterone, free testosterone swung about ten times more between peak and trough on injections (26.7 pg/mL) than on a gel (2.7 pg/mL). The Endocrine Society lists swings in mood or libido as an injection-specific effect. [5], [1]
• Breathing in sleep. Small studies suggest testosterone changes how the brain controls breathing during sleep, rather than narrowing the airway itself. [38], [39], [40]

What does the research show?

In controlled trials with a placebo group, the most consistent change on testosterone is a rise in hematocrit. Two pooled reviews also found slightly more prostate-related events, a small difference in absolute terms. Most other effects were uncommon, and stopping because of side effects was about as common on testosterone as on placebo. [41], [42], [3]

What do the pooled trial reviews find?

Stopping because of side effects was uncommon either way: about 3 in 100 men over 3 to 12 months in the Cochrane estimate, no more than on placebo, and slightly more on testosterone in the 2017 analysis, within a range that includes no difference. [3], [4]

Real-world use looks different. In US insurance records of 15,435 men starting a gel, only 34.7% were still filling prescriptions at 6 months, but the records do not say why men stopped. [44]

What about studies that used much higher doses?

Several often-quoted studies gave healthy men 250 to 600 mg a week to test how the body responds to very high levels (shorter sleep, more breathing pauses, mania-like symptoms in a few men). These are research doses, not treatment protocols, and this guide labels them wherever they appear. [39], [45], [46]

Is TRT safe, and which side effects are serious?

Is TRT safe?

For men with confirmed low testosterone who are monitored, testosterone therapy has a long record as standard treatment, and its main risks are well known and checked on routine tests. What remains uncertain is its long-term safety for the heart and prostate beyond about 2 years, and for forms other than the gel tested in the largest safety trial. [1], [47], [8]

What did the largest safety trial show?

TRAVERSE compared a daily testosterone gel with a placebo gel in about 5,200 men aged 45 to 80 with heart disease or high heart risk. Heart attack, stroke or cardiovascular death occurred in 182 of 2,596 men on testosterone (7.0%) and 190 of 2,602 on placebo (7.3%) (hazard ratio 0.96), which met the trial's safety goal. In the same two groups of about 2,600 men, some problems were more common on testosterone: atrial fibrillation 3.5% vs 2.4%, acute kidney injury 2.3% vs 1.5%, and pulmonary embolism 0.9% vs 0.5%. Fractures occurred in 91 of 2,601 men (3.50%) vs 64 of 2,603 (2.46%). In a prostate substudy, high-grade prostate cancer occurred in 5 of 2,596 men on testosterone (0.19%) vs 3 of 2,602 on placebo (0.12%), a difference that was not significant; men with a PSA above 3.0 ng/mL or severe urinary symptoms were excluded. [47], [8], [48], [18]

Its limits matter: it tested only a daily gel, men used it for an average of 21.7 months, about 61% stopped their study gel early, and it enrolled only men at high heart risk. [47], [8] The TRT and heart health guide covers the trial in full.

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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.

Which symptoms need prompt medical care?

The US labels and patient leaflets tell men to contact a clinician promptly for these. This list comes from the labels; it is not a personal plan.

• Signs of a blood clot: pain, swelling, warmth or redness in one leg, or sudden shortness of breath. Blood clots in the legs and lungs are listed warnings, and TRAVERSE found more pulmonary embolism on testosterone. [6], [8]
• A cough fit, throat tightness or trouble breathing during or right after an undecanoate (Aveed) injection. Aveed carries a boxed warning for pulmonary oil microembolism (POME) and allergic reactions, and men are watched for 30 minutes after every injection. [11]
• An erection that lasts too long or happens too often. The labels list priapism and tell men to report "too frequent or persistent erections". [12]
• Yellow skin or eyes, which can mean liver problems. [49], [6]
• New or worse depression, or thoughts of suicide. The Xyosted and Jatenzo labels carry a depression and suicide warning (see mood). [6], [9]
• Breathing pauses or gasping at night, which can mean new or worse sleep apnea. [6]
• Changes in a child around you, such as early signs of puberty, after contact with a gel user's skin. [20]

Who should be especially cautious?

• Men with sleep apnea that is untreated or severe. The Endocrine Society and the VA list untreated severe sleep apnea as a reason not to start; the Endocrine Society of Australia lists it as a precaution. [1], [24], [2]
• Men with heart failure, kidney or liver disease. Fluid retention can be serious in these conditions, and the VA lists poorly controlled heart failure as a reason not to start. [35], [24]
• Men with high blood pressure, because every product raises it a little; some labels advise against use when it is uncontrolled. [7], [27]
• Men who start with a high hematocrit, or who have had a clot without a clear trigger or have an inherited clotting disorder. See hematocrit on TRT. [1], [24]
• Men with prostate or breast cancer, or a high PSA not yet checked by a urologist. [1]
• Men who want children now or soon, because testosterone lowers sperm production. See TRT and fertility. [1], [6]
• Men with depression or a history of it, given the label warnings above. [6]
• Drug-tested athletes. Testosterone is prohibited in sport at all times. A therapeutic use exemption is possible only for low testosterone with a clear medical cause, and a prescription alone does not grant one. [14], [50]
• Under-18s. Testosterone for teenagers belongs only in specialist care.
• Women. This guide is written for men. Testosterone for women uses different doses and products; see testosterone therapy for women.

Which medicines and supplements matter?

• Corticosteroids (such as prednisone). Taken with testosterone, they may increase fluid retention. [35]
• Blood thinners, insulin and diabetes medicines. Testosterone can change the effect of oral blood thinners and can lower blood sugar and insulin needs; the labels list both. [12], [31]
• SGLT2 inhibitor diabetes medicines (such as empagliflozin) raise hematocrit on their own, and UK testosterone labels now warn about the combination. See medicines that raise hematocrit. [51]
• Finasteride and dutasteride (5-alpha-reductase inhibitors, used for hair loss and prostate enlargement) lower PSA. In a small trial in men on TRT, dutasteride lowered PSA by 0.46 ng/mL, which changes how a PSA result should be read. Finasteride 1 mg has its own sexual side effects on its label. See hair loss. [52], [53]
• Aromatase inhibitors such as anastrozole are sometimes added to lower estradiol, but they are off-label in men. The VA advises against them in general, and in older men anastrozole lowered spine bone density. See anastrozole. [54], [24], [55]

Bring a complete list of what you take, including supplements, to a pharmacist or prescriber. Checked September 2026.

Is testosterone legal, and is it allowed in sport?

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

• United States. Testosterone and its esters are Schedule III controlled substances, prescription only. No proposal to change that had been published as of September 2026. [13]
• United Kingdom. Testosterone is a Class C controlled drug under the Misuse of Drugs Act 1971 and is in Schedule 4 Part II of the Misuse of Drugs Regulations 2001. [56], [57]
• Canada. Testosterone is a Schedule IV controlled substance. [58]
• Australia. Testosterone is a Schedule 4 prescription-only medicine. [59]
• Sport. The World Anti-Doping Agency (WADA) prohibits testosterone at all times, and its 2027 list, published in September 2026, keeps the ban. Athletes with low testosterone from a clear medical cause can apply for a therapeutic use exemption, which is not guaranteed. [14], [60], [50]

US label changes. Since 2016, all testosterone labels warn about abuse and dependence. In February 2025, FDA made blood pressure a class-wide warning, and in July 2025 it removed the boxed blood-pressure warnings from Xyosted, Jatenzo, Tlando and Kyzatrex. Boxed warnings remain for Aveed (POME and allergic reactions) and for gels and solutions (transfer to others). [61], [7], [62], [11], [20]

Requested, not yet in the labels. On June 18, 2026, the US Department of Health and Human Services (HHS) announced that FDA is requesting three label changes: dropping the limitation on use for age-related low testosterone, contraindicating testosterone only in prostate cancer that has spread, and revising the warning about an enlarged prostate. These are requests. As of September 2026, current labels still carry the old wording. [63], [64]

What do guidelines say to do about side effects?

Guidelines usually adjust before stopping: a lower dose, a different interval or a different form. This section describes the choices clinicians weigh; it is not a personal plan. [1], [10]

What guidelines do not recommend as a first step: adding an aromatase inhibitor. The AUA considers one only when breast symptoms persist with a high estradiol while on-treatment testosterone is low or normal; when testosterone is in the upper normal range, it lowers the dose instead. The VA advises against them in general. [21], [24] The estrogen on TRT guide covers why estradiol that is pushed too low causes its own problems.

Skin, hair, breasts, swelling and testicles

Does TRT cause acne?

It can, and acne with oily skin is one of the side effects with the clearest evidence. In product trials it affected from about 1 in 100 men to about 1 in 12, and it rose with the dose: on AndroGel 1%, from 1% at 50 mg a day to 8% at 100 mg. [1], [19], [11], [65]

How long does it last? The clearest time course comes from trans men starting testosterone, a different group with a different starting point: acne peaked around 6 months, and after about 10 years 93.9% had no or mild acne. In a study of 323 trans men, acne was more likely with younger age, higher weight, testosterone above 10 nmol/L (about 288 ng/dL) and acne before starting. [66], [67]

What helps? Because acne tracks dose and level, prescribers may lower the dose, though no trial has tested how often that clears it, or whether more frequent injections help. Standard treatment still works: in 55 people whose acne came with testosterone, isotretinoin (a prescription acne medicine) improved it in 48 and cleared it in 26, with no comparison group. [19], [67], [68]

Does TRT cause hair loss?

It can speed up male-pattern hair loss in men who are prone to it, but how often is not known. The Endocrine Society lists "male pattern balding (familial)" among side effects with weak evidence, and in the AndroGel 1% trial hair loss affected 1% of men or fewer at each dose. No study has measured how many men with low testosterone develop new or faster hair loss on TRT. [1], [2], [19]

Numbers you may see online often come from trans men, whose hair started with a female pattern (after about 10 years, 32.7% had mild and 31% moderate to severe loss). They do not transfer to men who already had adult male testosterone levels. [66], [69]

What about finasteride or dutasteride with TRT? Some men and prescribers add one. In trials of older men on testosterone, finasteride limited prostate growth without removing the gains in bone or strength, and dutasteride in men on TRT lowered PSA, with a trend toward worse sexual-function scores that was not statistically clear. Finasteride 1 mg lists lower libido (1.8% vs 1.3% on placebo) and erection problems (1.3% vs 0.7%) on its label. Both medicines lower PSA, so tell whoever reads your PSA. [70], [71], [52], [53]

Why are my nipples sore on TRT? Is it gynecomastia?

Breast tenderness is common, and true breast enlargement (gynecomastia) is uncommon. The labels say gynecomastia "may develop and may persist". In trials, breast enlargement affected 0% to 3% of men on AndroGel 1% depending on the dose and 2.5% over its 3-year extension; "sensitive nipples" affected fewer than 1% on Testim. [1], [21], [6], [19], [28]

Does it go away? Sometimes: the AUA suggests watching new breast symptoms because they sometimes settle, and in a small trial gynecomastia resolved in 4 of 10 men on a patch and 1 of 9 on injections every 2 weeks. No study has found an estradiol level that predicts it on TRT. [21], [34]

What do guidelines do? The AUA checks estradiol when there are breast symptoms. If symptoms persist with a high estradiol, it lowers the testosterone dose when on-treatment testosterone is in the upper normal range. A lump, one-sided swelling or nipple discharge needs a clinician's examination. See tamoxifen and estrogen on TRT. [21]

Does TRT cause water retention or bloating?

Some men hold extra water, usually mildly. In a year-long trial, leg swelling affected 5.5% of men on oral undecanoate and 1.3% on a gel; it was 2.7% on Xyosted and under 1% on AndroGel 1%. The labels warn that swelling, with or without heart failure, can be serious in men with heart, kidney or liver disease, and that corticosteroids add to it. [65], [6], [19], [35]

No study has measured "facial bloat" or how much early weight gain on TRT is water. [72]

Will TRT shrink my testicles?

It can, and UK labels list smaller testicles as a common effect at high doses. Testicles are mostly sperm-making tissue, and testosterone from outside switches off the signals that keep it working. In a contraceptive study of 39 healthy men on enanthate injections, average testicle volume fell by 16.5% to 19.0% in 4 months, the shrinkage tracked the fall in sperm count, and size returned to normal after stopping. The study does not show how often this happens on routine TRT. [37], [72]

Sperm production falls too: in a World Health Organization contraceptive trial, 65% of men on 200 mg of enanthate a week had no sperm within 6 months. It usually returns after stopping, although US labels warn that reduced fertility may not reverse for some men. [73], [74], [6]

Does hCG stop the shrinkage? That is not established. hCG, a hormone that acts like LH, kept testosterone inside the testicles near normal in a 3-week research study, and in 26 men on TRT with hCG none lost all sperm, but these studies measured hormones and sperm, not testicle size. hCG protocols are in the hCG guide, and the TRT and fertility guide covers the options. [36], [75]

Sleep, mood, energy and headaches

Can TRT cause or worsen sleep apnea?

It may, in some men, early on; the evidence is thin and guidelines disagree. Obstructive sleep apnea means the airway keeps closing during sleep, causing breathing pauses and oxygen drops.

• The only placebo-controlled trial in men with sleep apnea. In 67 obese men with severe sleep apnea on a diet, undecanoate injections worsened nighttime oxygen drops by 10.3 events an hour at 7 weeks compared with placebo, but not at 18 weeks. [76]
• T4DM. In this 2-year trial in men aged 50 to 74 with prediabetes or new type 2 diabetes, who did not have diagnosed hypogonadism, a new diagnosis of sleep apnea was more common on undecanoate injections than on placebo during the trial (3.0% vs 0.4%) but not after it. A quarter of the men already had sleep apnea at entry. [77]
• Pooled trials and product trials. The 2005 meta-analysis found no more sleep apnea on testosterone, and the Endocrine Society says it has been "very low" in randomized trials. In the Xyosted trial, 2.0% of men were diagnosed with sleep apnea. [42], [1], [6]
• Records and small studies. In a US military health-records study (cohort study), sleep apnea was diagnosed within 2 years in 16.5% of men on TRT and 12.7% of matched men, though men on treatment may simply be tested more. In small older studies, breathing events during sleep rose on treatment. [78], [38], [79]

What does this mean in practice? The labels warn that testosterone may make sleep apnea worse, especially with obesity or chronic lung disease; the Endocrine Society and the VA advise against starting with untreated severe sleep apnea, while the European urology guideline sees no evidence of harm in mild, moderate or CPAP-treated sleep apnea. Treating sleep apnea with CPAP did not reliably raise testosterone in a meta-analysis, but weight loss did. [6], [1], [24], [22], [80], [81]

Can TRT cause insomnia or poor sleep?

A few men report it, but how often testosterone causes it is not known. In the placebo-controlled Testim trial, insomnia affected 1% of men on 50 mg, none on 100 mg and none on placebo, numbers too small to show an effect. In trials without a placebo, trouble sleeping affected 2.3% of men on Xyosted and 2% on Aveed. In a placebo-controlled trial of a gel in men with low testosterone caused by opioid painkillers, insomnia scores did not differ, and in TRAVERSE testosterone did not improve sleep quality. [6], [11], [28], [82], [83]

Does TRT cause mood swings, anxiety or anger?

At replacement doses, restoring low testosterone more often lowers irritability than raises it, but a minority of men report mood swings, and two labels carry a depression warning.

• Restoring low testosterone. In 51 hypogonadal men, anger, irritability and nervousness fell on treatment (no placebo group). In placebo-controlled trials, depressive symptoms improved by a small amount: 0.72 points on a standard depression scale in the Testosterone Trials, and a small effect in a meta-analysis of 27 trials. [84], [85], [86]
• Label signals. Mood swings, anger or aggression affected 2.6% of men on AndroGel 1.62% and none on placebo. In the Xyosted trials, 4 of 283 men (1.4%) had depression needing them to stop or made suicide attempts, and the Jatenzo label reports new or worse depression in 2 of 166 men. FDA later found no clear evidence that Xyosted carries a higher risk than other testosterone products, and both labels carry a warning. [20], [11], [6], [9], [87]
• Peaks and troughs. The Endocrine Society lists mood or libido swings as an injection-specific effect, and the Endocrine Society of Australia links swings in mood, libido and hot flushes to stop-start treatment or fluctuating levels. [1], [2]
• High research doses. At 600 mg of cypionate a week, 6 times a replacement dose, 12% of healthy men became mildly and 4% markedly hypomanic (hypomania is an abnormally high, driven mood). Across human experiments, giving testosterone had no clear effect on aggression. These are not TRT effects; see TRT vs steroids. [45], [88]

UK labels say irritability and nervousness can mean too much androgen and a reason to review the dose. Dependence has not been documented at approved doses, although after T4DM more former testosterone users restarted it (6% vs 2.8%), which the authors called consistent with dependence in some men. The TRT and mental health guide covers mood in depth. [51], [12], [77]

Why do I get hot flushes or night sweats on TRT?

Hot flushes in men come mainly from low estradiol. In experiments that switched off men's own hormones, flushes appeared at 26% of visits, and more often when estradiol was also blocked. On TRT they usually point to levels falling, for example late in an injection interval, after stopping, or when an aromatase inhibitor pushes estradiol too low. Aveed lists increased sweating in 1.3% of men and Testim hot flushes in 1%. [89], [2], [11], [28]

Does TRT cause headaches?

Headache appears in most product trials, usually in about 2% to 5% of men: 5.3% on Xyosted, 4.8% on Jatenzo, 5% on the 2% solution and 3.8% on Natesto. None of these trials had a placebo group, so how many headaches testosterone itself causes is not known. [6], [9], [27], [30]

Blood pressure, cholesterol, liver, red cells and prostate

Does TRT raise blood pressure?

Yes, a little, with every product. FDA's 24-hour blood-pressure studies confirmed a class-wide effect. In those studies, average systolic pressure (the top number) rose by these amounts:

[7], [9], [29], [90], [6], [11], [91], [8]

These were single-arm studies, so they show the change on treatment, not the difference from placebo. In TRAVERSE, which had a placebo, systolic pressure rose 1.0 mm Hg on the gel and fell 0.5 mm Hg on placebo by 36 months. On Xyosted, 10% of men started or changed blood-pressure medicine over a year, and Jatenzo raised heart rate by 2.2 beats a minute on average. [8], [6], [9]

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How much each product raised blood pressure

Average rise in 24-hour systolic pressure (the top number), mm Hg, in the US label monitoring studies.

Bars run from 0 to 5 mm Hg.

Jatenzo (oral undecanoate)

+4.9 / 2.5 mm Hg · about 4 months

Tlando (oral undecanoate)

+4.3 / 1.4 mm Hg · 4 months; published study: 3.8 systolic

Xyosted (under-the-skin enanthate)

+3.9 / 1.5 mm Hg · 12 weeks

Aveed (undecanoate injection)

+3.1 / 2.0 mm Hg · 16 weeks

AndroGel 1.62% (gel)

+1.9 mm Hg · 16 weeks

Kyzatrex (oral undecanoate)

+1.7 / 0.6 mm Hg · 4 months

With a placebo group

TRAVERSE: gel vs placebo gel

+1.5 mm Hg · Difference from placebo at 36 months (+1.0 vs −0.5)

Single-arm studies of different lengths: they show the change on each product, not a ranking or a difference from placebo.

The pooled evidence disagrees. The large TestES analysis found no harmful effect on blood pressure, while a smaller Chinese-language meta-analysis found higher pressure. In one placebo-controlled trial, the rise was larger in men whose hematocrit rose more. [43], [92], [93]

Does TRT affect cholesterol?

It lowers HDL, the "good" cholesterol, a little, and often lowers total and LDL cholesterol too. In older injection studies, HDL fell by about 4 mg/dL; a meta-analysis of 51 studies found an average fall of 0.49 mg/dL; and over 2 years on Jatenzo, HDL fell by 9.8 mg/dL. The TestES analysis of randomized trials found no harmful effect on cholesterol overall. The labels advise checking cholesterol periodically. [94], [17], [95], [43], [6]

Is TRT bad for the liver?

Serious liver injury is linked mainly to an older type of pill, the 17-alpha-alkylated methyltestosterone, which the AUA advises against. Oral testosterone undecanoate is different. The Kyzatrex label says it "is not known to cause hepatic adverse effects", and liver tests did not change meaningfully over 2 years on Jatenzo. The labels still mention liver tumors reported after long-term, high-dose use of androgens, including long-term enanthate injections. [49], [21], [8], [95], [6], [96]

Red blood cells, blood clots and the heart

• Red cells. Hematocrit rises about 3 points on average and is the most frequent side effect in trials; in the T4DM trial, hematocrit went above 54% in 22% of men on undecanoate injections (106 of 491) vs 1% on placebo (6 of 484). The hematocrit guide covers the numbers, causes and what lowers it. [17], [42], [97]
• Heart and blood clots. In TRAVERSE, heart attack, stroke or cardiovascular death occurred in 7.0% of men on testosterone gel and 7.3% on placebo gel (hazard ratio 0.96), which met the trial's safety goal. Atrial fibrillation (3.5% vs 2.4%), acute kidney injury (2.3% vs 1.5%) and pulmonary embolism (0.9% vs 0.5%) were more common on testosterone, and clots in veins occurred in 1.7% vs 1.2%. The trial tested only a gel, in men at high heart risk, for an average of 21.7 months, and about 61% stopped early. See what TRAVERSE showed and the heart health guide. [47], [8]

Does TRT affect the prostate or urination?

PSA rises slightly in the first months, and urinary symptoms did not worsen in trials, which mostly left out men with severe urinary symptoms. In TRAVERSE, PSA rose about 0.15 ng/mL more than on placebo at 12 months, and high-grade prostate cancer was not significantly more common (see what TRAVERSE showed). In a meta-analysis of 14 trials, urinary symptom scores changed by −0.41 points on testosterone and +0.12 on placebo, no real difference. The Endocrine Society refers to urology for a confirmed PSA rise of more than 1.4 ng/mL in the first year. The TRT and prostate guide covers PSA in full. [18], [98], [1]

Does TRT affect fertility and sex drive?

It lowers sperm production (see testicles), so men who want children soon need a different plan; see TRT and fertility. Sex drive usually improves, but some men report lower libido or erection problems on treatment; the labels list "increased or decreased libido", and the TRT and sexual health guide covers why. [12], [99]

What side effects does each form cause?

Every form shares the effects above; each also has its own. No trial has compared all forms head to head for overall side effects, so no form can be called the best tolerated. [1]

Injections: pain, lumps and site reactions

Reactions where the needle went in are the most common injection problem, and they are usually mild. Any injection-site reaction affected 12.7% of 283 men on Xyosted (none stopped), yet more than 95% reported no injection pain. Azmiro caused mild redness in 26% of men after one dose. Aveed caused injection pain in 4.6%. In an older trial, every-2-week enanthate injections into muscle caused local reactions in 33% of men. [6], [100], [101], [31], [11], [34]

Is subcutaneous injection less painful than intramuscular? No randomized trial in men with low testosterone has compared them. In 63 trans men on weekly subcutaneous (into the fatty layer under the skin) injections, 9 had minor, short-lived reactions, and the 22 who had switched from intramuscular (into a muscle) injections all preferred subcutaneous. The injection guide covers technique and site rotation. [102]

Why do some men cough right after an injection?

Oil injected into muscle can occasionally reach the lungs as tiny droplets, a reaction called pulmonary oil microembolism (POME). It causes a sudden urge to cough, shortness of breath or throat tightness, usually during or just after the injection, and most episodes pass within minutes.

• Undecanoate injections (Aveed, Nebido). In one clinic's watched injections, it happened after 56 of 3,022 injections (19 per 1,000), 66% mild. Across 18 trials of undecanoate injections, 9 events occurred in 8 of 3,556 men. After Aveed went on sale, 28 cases were reported while 90,092 doses were shipped, and most that had a recorded time resolved within 30 minutes. Shipped doses are not the same as injections given, and reports can be missed. The rates differ because watching every injection catches more than waiting for reports. [103], [11], [104]
• Cypionate and enanthate. The Endocrine Society lists coughing right after injections as a form-specific effect; it is reported more rarely than with undecanoate. [1]

Because of the risk of serious POME and allergic reactions, Aveed is available only through a safety program (REMS): certified providers give it in certified healthcare settings, with 30 minutes of observation after every injection. Checked September 2026. [11]

Gels, solutions and patches: skin reactions and transfer

Skin reactions where a transdermal product (absorbed through the skin) is applied affected 0.9% of men on AndroGel 1.62%, 3% to 5% on AndroGel 1%, 2% to 4% on Testim (3% on placebo) and up to 7% on the underarm solution. Patches caused far more: skin irritation affected 66% of men on an older patch against 5.5% on a gel, [20], [19], [28], [27], [105] Testosterone patches are no longer sold in the US (checked September 2026). [106]

The bigger risk with gels is transfer: all US gels and solutions carry a boxed warning because children have developed early signs of puberty after skin contact with a user. The testosterone gel guide covers how to prevent it. [20]

Nasal gel, oral capsules and pellets

• Natesto (nasal gel). Headache, runny nose, nosebleeds, nasal discomfort and nasal scabs each affected 3.8% of men, and a changed sense of smell affected 4 of 69 men (5.8%) through the first extension. See Natesto. [30]
• Oral undecanoate (Jatenzo, Kyzatrex, Tlando). Jatenzo and Tlando had two of the larger average blood-pressure rises in their label studies, while Kyzatrex had the smallest; separate studies cannot rank forms. They also cause some stomach effects: nausea in 2.4% on Jatenzo, with diarrhea and burping in more than 2% across its trials. Leg swelling was more common than on a gel in one trial. See oral testosterone. [9], [29], [8], [65]
• Pellets (Testopel). The label lists infection at the implant site and pellets working their way out. See testosterone pellets. [107]

Do side effects go away?

Many do. In trans men, acne peaked around 6 months and then settled for most. Breast symptoms sometimes settle, the AUA notes. The worsening of breathing in sleep seen at 7 weeks in one trial was gone by 18 weeks. Testicles returned to normal size after stopping in a contraceptive study. Long-acting injections are the exception: the UK Sustanon label notes that side effects "cannot be quickly reversed" by stopping, because the medicine stays in the body for weeks. [66], [21], [76], [37], [108]

If treatment stops, low-testosterone symptoms usually come back, and the body's own production can take months to recover. The stopping TRT guide covers what to expect. [10]

What do people on TRT report about side effects?

Public forums are full of men trying to work out whether a new symptom comes from testosterone, the dose, an added medicine or something else. The threads below are recent public Reddit discussions, read with their replies; they show what people experience, not how often it happens. Accounts involving doses above replacement or unregulated products were left out.

Acne, hair and skin

Several accounts describe chest or back acne after a dose increase. One man's back acne began when he went from 150 to 200 mg a week, despite injecting every other day; another's chest acne and night sweats appeared months after a rise from 120 to 140 mg, and isotretinoin cleared his face before his chest. One man credited splitting the same weekly volume into three injections, though his weight and diet changed too. [109], [110], [111]

Hair stories turn on timing. One man noticed crown thinning 3 months in, then admitted he had never looked closely before starting. Another's shedding began after he added hCG and a brief course of an aromatase inhibitor, and continued a month after he stopped both. One man who added finasteride for faster hair loss described weaker erections and mood swings. [112], [113], [114]

Nipples, estradiol and water

Tender nipples are common; confirmed breast enlargement is not. One man's tenderness continued across several normal estradiol results, and when an aromatase inhibitor had earlier pushed his estradiol to 8, he felt unwell and lost sexual function. Another's hard tissue under both nipples was almost gone 6 days after he stopped finasteride, which he had started alongside TRT. A tender lump sent a third man for an ultrasound, which found glandular tissue, with a mammogram pending. [115], [116], [117]

Threads about a "crashed E2" are a warning in themselves: men describe joint pain, stiffness, anxiety and loss of sexual function after aromatase inhibitors or over-the-counter estrogen blockers, improving after they stopped. See estrogen on TRT. Early water weight often passes, as it did for one man who gained about 5 lb; facial bloating comes up most at higher doses. [118], [119], [120], [121]

Testicles

Experiences range widely. One man described his testicles as about 30% smaller but did not mind, with good sexual function. Another's size improved in the first month of hCG and partly shrank again by the third; a third had used hCG for most of 3 years without restoring size, and his main problem was discomfort. [122], [123], [124]

Sleep, anxiety and mood

These are the hardest to pin on testosterone, because so much else changes at once. One man woke gasping 14 weeks in and was told to stop until a sleep study; reflux was also found. Another, 5 weeks into 50 mg once a week, felt anxious with swings that eased the day after each injection, alongside a history of health anxiety. One man's insomnia began after an aromatase inhibitor, dose cuts and major weight loss, and he later found low blood sugar. Schedule changes cut both ways: one man felt better splitting his weekly dose into two injections, another worse after moving to every 3 days. [125], [126], [127], [128], [129]

Blood pressure and injections

One man developed a pounding heartbeat, with a raised hematocrit and a reading of 201/105 that sent him to hospital; a blood-pressure medicine and a lower dose helped. Another's high readings were partly explained by coffee and a large meal. [130], [131]

Pain after a first injection into a new site, such as the side of the hip or the shoulder, is common. One man's itching and bruising at under-the-skin belly sites stopped when he moved to injections into muscle, while others find under-the-skin injections less painful; one man's redness and burning cleared when he changed to a product in a different carrier oil. [132], [133], [134], [135], [136]

How can you judge a side-effect story?

Ask: What was the dose in mg, how often, and was it prescribed? When did the symptom start, and what else changed around then, such as a dose increase, an aromatase inhibitor, finasteride, hCG, a weight-loss medicine, alcohol or cannabis? Was there a blood test at the time, and when was it drawn? Did the symptom exist before TRT? And what happened a few 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 side-effect rate or a substitute for the studies above.

What should you track?

How you feel and what changed, at every visit, plus hematocrit, PSA, blood pressure and cholesterol on the schedule your guideline and label set. Use this summary to prepare questions for your prescriber; it is not a personal testing plan. [1], [6]

[1], [10], [25], [24], [23], [6], [12]

Write down when a symptom started and what changed: the dose, the injection day, any new medicine and the timing of your last blood test. The testosterone level visualizer shows how injection frequency changes peaks and troughs.

Common questions about TRT side effects

What are the most common side effects of TRT?

A rise in red blood cells (hematocrit), acne and oily skin, and lower sperm production have the clearest evidence. In product trials, a higher hematocrit, a rise in PSA, high blood pressure, headache and reactions where the medicine is injected or applied were among the most frequently reported. [1], [6], [20] See the key numbers.

How long do TRT side effects last?

Many settle within months: acne tends to peak around 6 months, breast symptoms sometimes settle, and early changes in sleep breathing faded by 18 weeks in one trial. Others, such as a higher hematocrit and smaller testicles, last as long as treatment does; in a contraceptive study, testicle size returned to normal after stopping. [66], [21], [76], [37] See do side effects go away.

Can TRT make you angry or anxious?

A minority of men report mood swings, irritability or anxiety, often tied to peaks and troughs on injections; restoring low testosterone more often lowers irritability. The anger and mania reported in some studies came from research doses several times higher than TRT. [20], [84], [45] See mood.

Are injections or gels better for side effects?

Neither is better overall. Injections raise hematocrit more and swing levels more; gels cause skin reactions and carry a transfer risk; every form raises blood pressure a little, and separate label studies cannot rank them; nasal gel causes nasal symptoms. No trial has ranked them. [5], [20], [7], [30] See side effects by form.

Which side effects mean I should stop TRT?

Guidelines usually adjust before stopping, but the CUA stops treatment for significant side effects, with no taper needed, and the Endocrine Society stops it while hematocrit is above 54%. Signs of a clot, a serious reaction after an injection or thoughts of self-harm need prompt care. [10], [1], [6] See urgent symptoms.

Glossary

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

5-alpha-reductase inhibitor

A medicine, such as finasteride or dutasteride, that blocks the enzyme turning testosterone into DHT. Used for male-pattern hair loss and an enlarged prostate. It lowers PSA.

Acne

Blocked, inflamed pores that form spots, often on the face, chest and back. Testosterone makes it more likely by increasing skin oil.

Boxed warning

The strongest warning on a US medicine label, printed in a box at the top. For testosterone it applies to Aveed injections and to gels and solutions.

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.

CPAP

Continuous positive airway pressure: a bedside machine that blows air through a mask to keep the airway open during sleep. It is the standard treatment for obstructive sleep apnea.

DHT (dihydrotestosterone)

A stronger androgen the body makes from testosterone, especially in the skin, hair follicles and prostate.

Estradiol

The main estrogen. Men make it from testosterone, and they need some of it for bone, sexual function and mood.

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

Enlargement of the glandular breast tissue in men, felt as a firm disc under the nipple. It is different from fat in the chest area.

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.

HDL cholesterol

High-density lipoprotein, often called the good cholesterol because higher levels go with lower heart risk. Testosterone lowers it slightly.

Hematocrit

The share of the blood made up of red blood cells. Testosterone therapy can raise it, which is why it is checked.

Hypomania

A period of abnormally high, driven or irritable mood with more energy and less need for sleep, milder than full mania.

Intramuscular (IM)

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

L/L (liters per liter)

A way of writing hematocrit as a fraction instead of a percentage. 0.54 L/L is the same as 54%.

Product label (prescribing information)

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

LH and FSH

Luteinizing hormone and follicle-stimulating hormone: the pituitary gland's two signals to the testicles, telling them to make testosterone and sperm. Testosterone therapy switches them down.

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. A network meta-analysis compares several treatments at once.

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.

Parosmia

A changed or distorted sense of smell, reported with nasal testosterone.

Placebo

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

Pulmonary oil microembolism (POME)

Tiny droplets of injected oil reaching the lungs, causing a sudden cough, shortness of breath or throat tightness during or just after an injection. Most episodes pass within minutes.

Priapism

A painful erection lasting hours without sexual stimulation. It is a medical emergency.

PSA (prostate-specific antigen)

A protein made by the prostate and measured in blood. It rises slightly on testosterone and is used to decide when to refer to a urologist.

Relative risk

How much more or less likely an event is in one group than another. A relative risk of 0.81 means about 19% less likely; 1 means no difference.

REMS

Risk Evaluation and Mitigation Strategy: an FDA-required safety program. For Aveed, certified providers give it in certified healthcare settings, and men are observed for 30 minutes after each injection.

Sebum

The oily substance made by glands in the skin next to each hair follicle. More sebum makes acne and oily skin more likely.

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, and some prescribers use this route for other testosterone injections.

Transdermal

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

Trough level

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

TRT (testosterone replacement therapy)

Prescribed testosterone, by injection, gel or other forms, for men with low testosterone.

WADA

The World Anti-Doping Agency, which publishes the list of substances banned in sport. Testosterone is prohibited 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 9 medical bodies, current product labels from the US and UK, published clinical trials, reviews and studies, and regulatory documents. We also reviewed public online forums where men on TRT describe their own side effects.

The guide cites 136 sources, including 48 original studies in people, 14 reviews and meta-analyses, 9 clinical guidelines and position statements, 21 product labels and 28 public community discussions. Each type of source answers a different question. Guidelines and labels show what clinicians are told to do and what product trials recorded. Placebo-controlled trials and reviews show what testosterone itself causes. 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 the original, 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