Side Effects of Testosterone Therapy
The short version:
- The most common side effects of testosterone therapy — acne, fluid retention, mood changes, breast tenderness — are usually mild and manageable with dose adjustments.
- The serious risks — a high red blood cell count, blood clots, worsened sleep apnea — are less common and are exactly what regular blood monitoring exists to catch.
- On heart safety, the large 2023 TRAVERSE trial found no increase in major cardiac events in men with confirmed low testosterone.
- TRT isn’t for everyone: it suppresses fertility and is avoided with prostate cancer, male breast cancer, and untreated severe sleep apnea.
Testosterone replacement therapy (TRT) can be life-changing for men with confirmed low testosterone. But like any medical treatment, the side effects of testosterone therapy deserve your attention before you start — the common, manageable ones, the rare serious risks, and the situations where TRT shouldn’t be used at all. This guide covers all three, so you can make an informed decision with your doctor.
The good news up front: most side effects are manageable with proper monitoring and dose adjustment. The key is working with a specialist who understands TRT and catches potential issues early.
Common, Manageable Side Effects
These are the side effects men most often notice. They’re typically mild, and they often ease as the body adjusts to treatment. The table below covers both groups at a glance — the everyday, manageable effects first, then the rarer serious risks explained in the next section.
| Side effect | How common / serious | What to do about it |
|---|---|---|
| Acne and oily skin — testosterone increases sebum (skin oil), especially on the back, shoulders, and chest | One of the most frequently reported; typically mild | Keep the area clean, use non-comedogenic (non-pore-clogging) products, ask about topical treatments; often diminishes over time |
| Fluid retention — mild swelling in the legs, feet, or hands; sometimes slight weight gain | Common; usually mild | Monitor weight weekly, limit sodium, stay hydrated; if significant, your doctor may adjust the dose or, rarely, recommend diuretics |
| Mood swings or irritability — even though testosterone typically improves mood | Affects some men, particularly at higher doses | Keep a mood journal to spot patterns; dose adjustment usually resolves it, and exercise and stress management help |
| Breast tenderness or swelling (gynecomastia) — from testosterone converting to estrogen | Affects some men when estrogen rises too much | Dose reduction; if persistent, an estrogen blocker (aromatase inhibitor) |
| Polycythemia (high red blood cell count) — thickens the blood and raises clot risk | Less common; serious — the single most important lab value on TRT | Hematocrit checked every 3–6 months; if it climbs: lower dose, blood donation, or a treatment pause; stay hydrated |
| Blood clots — deep vein thrombosis (a clot in the leg) or pulmonary embolism (a clot in the lungs) | Rare, but serious | Keep hematocrit monitored; know the warning signs (see the alert below) and seek emergency care if they appear |
| Worsened sleep apnea — repeated pauses in breathing during sleep | Less common; serious in men who have apnea or are at risk | Tell your doctor about snoring or waking up gasping — a sleep study may be recommended; severe untreated apnea is addressed before therapy |
| Liver function changes — mainly with older oral forms; uncommon with injections or gels | Rare | Periodic liver function tests catch any issue early; treatment is adjusted if needed |
Serious Risks to Watch For
These are less common but require medical attention — and they’re the reason regular monitoring is non-negotiable, a point the Mayo Clinic’s overview of testosterone therapy risks makes clearly. The last four rows of the table above summarize them: polycythemia, blood clots, worsened sleep apnea, and (rarely, mainly with older oral forms) liver function changes.
Of these, polycythemia deserves the most attention. Testosterone stimulates red blood cell production, and too many red blood cells thicken the blood and raise clot risk — which is exactly why hematocrit (the red-blood-cell fraction of your blood) is the single most important lab value to monitor on TRT, and why elevated hematocrit is what links polycythemia to the clot risk in the row below it.
Seek emergency care immediately if you develop chest pain, shortness of breath, calf swelling, or leg pain — these are warning signs of a blood clot. Don’t wait.
Heart Safety: What the TRAVERSE Trial Showed
Heart attack and stroke risk is the concern men raise most — and the best evidence is reassuring. The landmark TRAVERSE trial, published in the New England Journal of Medicine in 2023, followed thousands of men with confirmed low testosterone and found no increased risk of major adverse cardiovascular events (heart attack or stroke) on testosterone therapy compared with placebo.
The honest caveat: the trial did note a somewhat higher rate of atrial fibrillation (an irregular heart rhythm) in the testosterone group. Your doctor should keep an eye on your heart rhythm, especially if you have risk factors — reassuring headline results don’t replace monitoring.
For the fuller picture of how testosterone and the heart interact, see testosterone and your heart.
Fertility: An Effect Every Younger Man Should Know About
Many men don’t learn this until too late: testosterone therapy suppresses sperm production.
When you take testosterone from outside the body, your brain senses plenty of the hormone and shuts down its signals to the testes — which halts both natural production and sperm creation. For most men on TRT, that means infertility while on treatment.
If you want biological children: raise it with your doctor before starting. Options include freezing sperm beforehand or using medications such as hCG (human chorionic gonadotropin) to help preserve fertility during therapy. After stopping TRT, sperm production typically recovers, but it can take weeks to months.
Prostate Health and Monitoring
Does testosterone cause prostate cancer? Current evidence shows no proven link — studies have not found higher prostate cancer rates in treated men compared with untreated men.
Testosterone can, however, cause modest prostate growth and raise PSA (prostate-specific antigen, a blood marker of prostate activity). That’s why a baseline PSA is checked before starting and monitored during treatment; a rapid or high rise triggers further investigation.
Contraindications: Who Shouldn’t Take Testosterone
TRT is only appropriate for men with confirmed deficiency — and even then, some situations rule it out or put it on hold.
Doctors generally advise against or delay testosterone therapy for men with:
- Prostate cancer or male breast cancer — active or suspected; a history of prostate cancer requires a careful case-by-case discussion with your oncologist and hormone specialist
- An unevaluated prostate abnormality — an elevated PSA or a nodule found on exam must be worked up first
- Plans to conceive in the near future — because TRT suppresses sperm production
- Untreated severe obstructive sleep apnea — treat the apnea first
- An already-high red blood cell count (elevated hematocrit) — this must be corrected before starting
- Severe untreated heart failure, or a very recent heart attack or stroke — stabilize first, then reassess
This is also why the FDA’s testosterone information page stresses that testosterone is a prescription treatment for diagnosed deficiency — not a general energy or performance booster. Proper diagnosis, with two morning blood tests, comes before any prescription; our testosterone testing guide explains that process.
Injection-Specific Side Effects
Injectable testosterone adds a few injection-site considerations:
- Injection-site pain and inflammation: tenderness, redness, or swelling; proper technique and rotating sites help
- Oil microembolism: rare but serious — a droplet of the oil-based solution enters a blood vessel, potentially causing brief chest pain or shortness of breath; correct technique minimizes the risk
- Nerve or blood vessel injury: extremely rare with proper technique, which your doctor should teach you
Gels trade these for possible skin irritation at the application site (and require care to avoid skin-to-skin transfer). For technique and safety details, see testosterone injections.
Side Effects in Women
Women prescribed testosterone use much lower doses, and at those low physiological doses side effects are uncommon. At higher doses, virilization (development of male-pattern features) becomes possible: acne, increased facial and body hair, voice deepening (which can be permanent), clitoral enlargement, and male-pattern hair loss.
Any woman considering therapy should discuss these trade-offs with her doctor — our testosterone for women page covers how female treatment differs.
How Side Effects Are Managed
Here’s the encouraging part: with proper medical supervision, most side effects are caught early and corrected without stopping treatment.
The key to safe TRT is working with a specialist who monitors you closely, adjusts doses thoughtfully, and listens to your concerns.
Monitoring follows a simple rhythm — a baseline before you start, closer checks in the early months, then routine follow-up:
| When | What gets checked |
|---|---|
| Before starting | Baseline PSA and hematocrit, cardiovascular risk assessment, and screening for contraindications (sleep apnea, prostate abnormalities) |
| Early months | Blood tests (testosterone, hematocrit, PSA, liver enzymes) every 3–6 months, plus blood pressure checks and body weight tracking |
| Ongoing | The same blood tests annually, with sleep quality evaluation and mood and behavioral check-ins at each visit |
Management strategies:
- Dose adjustment: lowering the dose often resolves side effects while keeping the benefits
- Changing delivery method: switching between injections, gels, and other forms can reduce specific side effects
- Medication support: aromatase inhibitors for estrogen-related effects; diuretics for stubborn fluid retention
- Lifestyle changes: exercise, diet, sleep, and stress management all pull in the same direction
- A treatment pause: rarely, temporarily stopping lets the body recover while your doctor reassesses
The specialist approach works: men treated by experienced doctors have fewer complications and better outcomes. Curious how therapy is actually structured — forms, dosing, and follow-up? See testosterone replacement therapy.
Your first step isn’t treatment — it’s information.
1. Get the data: a comprehensive blood panel plus a physical exam establish where you actually stand — hormones and beyond.
2. Let a doctor read the full picture: testosterone is one number among many. Your physician weighs your complete lab work, health history, and exam findings before deciding whether treatment would genuinely benefit your individual case.
FAQs
What are the most common side effects of TRT?
Acne, fluid retention, mood changes, and breast tenderness. All four are usually manageable with dose adjustment and routine monitoring.
Does testosterone therapy cause hair loss?
Not directly. But if you’re genetically predisposed to male-pattern baldness, testosterone can accelerate it. If that concerns you, ask your doctor about options such as finasteride.
Can testosterone therapy cause anger or mood swings?
Testosterone generally improves mood, but some men notice irritability or mood swings, especially at higher doses. It typically resolves with dose adjustment; exercise and stress management help.
Does TRT cause prostate cancer?
Studies show no link between testosterone therapy and developing prostate cancer. TRT can raise PSA slightly, though, so regular PSA monitoring is essential — and men with existing prostate cancer should not take testosterone without specialist guidance.
Are injection side effects different from gel side effects?
Yes. Injections carry injection-site risks (pain, inflammation, rare oil microembolism); gels can irritate the skin where applied. Both share the systemic effects covered above. Your doctor can help you choose the best-fitting method.
Can side effects be reversed by stopping TRT?
Most resolve within weeks to months after stopping. A few — voice deepening in women, significant hair loss — can be permanent. Never stop suddenly; taper and transition under your doctor’s guidance.
How is polycythemia managed during TRT?
With regular hematocrit checks. If levels rise, your doctor may reduce your dose, recommend blood donation (phlebotomy), increase your fluid intake, or pause treatment briefly. Most cases are managed without stopping TRT entirely.
References
- Lincoff AM, et al. Cardiovascular Safety of Testosterone-Replacement Therapy (TRAVERSE). N Engl J Med. 2023.
- U.S. Food & Drug Administration. Testosterone Information.
- Mayo Clinic. Testosterone Therapy: Potential Benefits and Risks as You Age.
- American Urological Association. Evaluation and Management of Testosterone Deficiency: AUA Guideline.
- Bhasin S, et al. Testosterone Therapy in Men with Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018.
Medical Disclaimer: The information on this page is for educational purposes only and is not intended as medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting, stopping, or changing any hormone therapy or medication. Individual results vary, and treatment decisions should be made between you and your doctor based on your specific medical history and needs.
National HRT Staff
Please note that the information provided in this article is for informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition or treatment.