Most men start testosterone replacement therapy with a pretty narrow checklist in their heads: more energy, better mood, stronger libido, maybe a little extra muscle at the gym. What they’re rarely told, or what gets glossed over in a ten-minute clinic visit, is the longer tail of side effects that can show up weeks or months in.
Some are mild. Some are the kind of thing you’d want to know about before you sign on for an indefinite prescription.
This isn’t a scare piece. Testosterone therapy is genuinely helpful for men with clinically low levels confirmed on bloodwork, and the FDA has approved multiple formulations for that use. But the side-effect profile is broader than the marketing suggests, and a few of these get missed in routine follow-up.
Why the Side Effects of Testosterone Replacement Therapy Get Overlooked
Part of the problem is framing. When a man feels better on therapy, he tends to attribute new symptoms to other causes: stress, aging, diet, work. The connection back to the prescription doesn’t get made. Prescribers, for their part, often monitor a focused set of labs (total testosterone, hematocrit, PSA) and may not catch the more subtle stuff unless the patient brings it up.
The American Urological Association guidelines outline the major risks clearly, but in clinic practice, the conversation often defaults to the highlights. Here are the seven side effects I see patients miss most often.
1. Thicker Blood (Erythrocytosis)
Testosterone stimulates red blood cell production. For some men, that pushes hematocrit above 54%, which raises the risk of clots, stroke, and heart attack. It’s one of the most common reasons therapy gets paused or dose-adjusted.
You won’t feel it. That’s the issue. It shows up on a routine CBC, which is exactly why scheduled bloodwork during testosterone replacement therapy isn’t optional.
If your hematocrit climbs, your prescriber may lower the dose, switch formulations, or recommend a therapeutic phlebotomy (basically a blood donation).
2. Sleep Apnea That Wasn’t There Before
Testosterone can worsen, or sometimes unmask, obstructive sleep apnea. Partners notice the snoring first. The man himself usually notices daytime fatigue and chalks it up to a busy week.
If you’re waking up groggy on therapy when you used to wake up sharp, mention it. A sleep study is cheap insurance.
3. Shrinking Testicles and Lower Fertility
This one surprises men more than any other. Exogenous testosterone shuts down the body’s own signal to the testes, which means they make less testosterone on their own and produce less sperm. Testicular size can drop noticeably within a few months.
For men trying to conceive, this matters a lot. The NIH has published on testosterone-related infertility, and the takeaway is that sperm counts can crash to zero in some men on standard therapy. There are workarounds (hCG, clomiphene, switching to alternatives) but you need to flag fertility as a goal up front. We cover the broader picture in our piece on what happens if low testosterone goes untreated, where the trade-offs get more attention.
4. Acne and Oily Skin That Feels Like Puberty Again
Sebaceous glands respond to androgens. A lot of men in their 40s and 50s find themselves dealing with breakouts on the back, shoulders, and chest within the first few months of therapy.
Usually manageable. Sometimes annoying enough to want to do something about it. Topical retinoids can help, and our breakdown of tretinoin vs adapalene walks through which option tends to suit which skin type.
5. Breast Tenderness or Enlargement (Gynecomastia)
Some of the testosterone you take gets converted to estradiol via aromatase. If that conversion runs high, you can end up with tender, swollen breast tissue. Not common, but not rare either.
Catching it early matters. Once gynecomastia has been established for more than 12 months, the tissue tends to fibrose, and medications stop working well. Surgery becomes the only fix.
6. Mood Swings, Irritability, and Anxiety
The narrative is that testosterone makes you feel great. For most men it does. But a meaningful subset, somewhere around 1 in 10 in my experience, report increased irritability, shorter fuse with family, or new anxiety, especially with injection-based protocols where levels peak hard and trough hard.
Switching to a more stable formulation, like a gel, a pellet, or one of the newer oral options, often smooths this out. So can splitting injections into smaller, more frequent doses. Talk to your prescriber before you stop on your own.
7. Cardiovascular Changes You Won’t Feel
The cardiovascular debate around testosterone replacement therapy has gone back and forth for a decade. The 2023 TRAVERSE trial, published in NEJM, found no overall increase in major cardiac events, but it did show modestly higher rates of atrial fibrillation, pulmonary embolism, and acute kidney injury in the testosterone group.
That’s not a reason to refuse therapy if you need it. It is a reason to make sure your blood pressure, lipids, and heart rhythm are getting monitored, particularly if you already have cardiac risk factors.
What to Actually Do With This Information
If you’re already on testosterone replacement therapy and any of this sounds familiar, don’t stop cold. Call your prescriber. Ask for a CBC, a PSA, an estradiol level, and a frank conversation about dose and formulation.
If you’re considering starting, get a proper workup first. Two morning testosterone levels below 300 ng/dL on separate days is the standard threshold, and our overview of normal testosterone levels by age can help you put your own numbers in context. If cost is a concern, you can compare TRT formulations and ED medications at edrugstore.com to see what fits your budget and prescriber’s plan.
Testosterone replacement therapy works well for the right patient at the right dose with the right monitoring. The men who run into trouble are almost always the ones who weren’t told what to watch for. Now you’ve been told.
This article is for informational purposes only and is not medical advice. Always consult a licensed pharmacist or physician before starting, stopping, or changing any medication.
References
- FDA Testosterone Information, official safety labeling and approved indications for testosterone products.
- American Urological Association Testosterone Deficiency Guideline, clinical standards for diagnosis, treatment, and monitoring.
- NIH / NCBI: Testosterone Therapy and Male Infertility, peer-reviewed evidence on fertility effects of exogenous testosterone.
- NEJM: TRAVERSE Cardiovascular Safety Trial, large randomized trial on cardiovascular outcomes with testosterone therapy.
Dr Steven Schlosser
Dr. Schlosser graduated from Lafayette College Phi Beta Kappa and attended Georgetown Medical School. He had 4 years of medical residency training at Tufts University in Boston in both Gynecology and Internal Medicine. He has had a spotless medical career for the past 40+ years and is Board Certified. Learn More