TRT Side Effects: What To Know Before Starting Treatment

Many TRT side effects are mild and can be managed with monitoring, but several can be serious. Acne, oily skin, fluid retention, breast tenderness, smaller testicles, and a lower sperm count are common. The one that needs the closest watch is a rise in red blood cells, which can thicken the blood. And in monitored men with low testosterone, the largest trial to date found no rise in heart attack or stroke, though it did flag other heart-related risks covered below (Lincoff et al., 2023).

Here is what most articles get wrong. The frightening TRT stories almost always come from unsupervised testosterone use, with no baseline labs and no follow-up. The molecule is not the problem. Poor monitoring is.

This is about medically supervised TRT for low testosterone, not bodybuilding doses or chasing performance. Those carry their own, much bigger risks.

The science shifted recently too. In February 2025, the FDA removed the cardiovascular boxed warning from all testosterone products and added a new warning about increased blood pressure, the first change driven by the large TRAVERSE trial and the second by required blood pressure studies (FDA, 2025). So the heart picture looks more reassuring than it did five years ago. Not risk-free, but better understood.

What is TRT, and why does it cause side effects?

TRT replaces testosterone your body is not making enough of on its own. Side effects happen because testosterone does not act in just one place. It touches your blood, your prostate, your skin, and the system that makes sperm.

Providers prescribe it as injections, skin gels, patches, pellets, or pills (FDA, 2025). It helps men whose low levels come from a medical problem with the testicles, the pituitary, or the hypothalamus, a condition called hypogonadism. It does not fix the root cause. It replaces the hormone, which is why stopping later takes planning.

How testosterone acts on the body

Testosterone can raise red blood cell production. Some of it converts to estrogen. It can stimulate prostate growth. And when you add it from outside, your body slows its own output, which can shrink the testicles and lower sperm count. Nearly every common side effect traces back to one of those four actions.

Aging lowers testosterone, but slowly

Testosterone does fall with age. The decline is gradual, and how much it falls varies from person to person.

A slow dip like that is normal. It is not the same as the medical low testosterone that TRT is approved to treat. That distinction matters for side effects, because as of 2025 the FDA still does not approve testosterone for men who are simply getting older (FDA, 2025). Take it for normal aging and you can accept the side-effect risk without a clear medical reason. Learn the symptoms of low testosterone before you assume age is the cause.

Are your symptoms from low testosterone, or something else?

Maybe not. Low energy, low sex drive, and brain fog overlap with plenty of other conditions.

Sleep apnea, thyroid trouble, diabetes, depression, and extra weight can all produce the same symptoms. That is why a good provider does not go by how you feel. They confirm low testosterone with blood testing, usually on more than one morning, before prescribing (Bhasin et al., 2018). Where your numbers fall against the reference range matters as much as the symptoms. Start TRT with normal levels and you may take on the risks with little likely benefit.

What TRT actually does, and what the latest data shows

It depends entirely on whether your testosterone is truly low.

For men with confirmed low testosterone, the Testosterone Trials found that treatment can improve sexual function, with a much smaller effect on energy and walking (Snyder et al., 2016). It can also raise bone density (Snyder et al., 2017). Those gains are real for men who are actually low. For a healthy man with normal levels chasing an edge, the math falls apart. The benefits shrink and the side effects stay. Men with mid-range numbers sometimes push for a prescription because a friend felt great on it. That is the wrong reason. If your levels are normal, you may take on side effects and ongoing monitoring with little likely benefit.

What are the most common TRT side effects?

The most common TRT side effects are acne or oily skin, fluid retention, breast tenderness, smaller testicles, a lower sperm count, and a rise in red blood cells. Most are mild. A few need closer attention.

Your provider chooses the form with you, based on your health, your preferences, and how you respond.

Sources: the Endocrine Society guideline (Bhasin et al., 2018) and the FDA (2025).

Too many red blood cells, the side effect that matters most

This is the one to take seriously. Testosterone can push your body to make more red blood cells, and too many of them can thicken the blood.

The medical name is erythrocytosis, or polycythemia. The Endocrine Society's review found it happens far more often on testosterone than on a placebo, and it is most common with injections (Bhasin et al., 2018). Guidelines are clear about acting on it. When your red blood cell count climbs too high, your provider may lower the dose, switch the form, or use a therapeutic blood draw to bring it down (Mulhall et al., 2018; Bhasin et al., 2018). This is usually manageable when someone is monitoring you. Skip the monitoring, though, and a high red blood cell count can raise your risk of blood clots. That is the entire reason baseline and repeat bloodwork matters.

What TRAVERSE changed about TRT and heart health

The biggest recent update is reassuring, with caveats.

TRAVERSE was a large trial of older men who had low testosterone plus heart disease or high heart risk (Lincoff et al., 2023). Testosterone did not raise the rate of major cardiac events, meaning heart attack, stroke, or cardiac death, compared to placebo. In a group that high-risk, that is a strong result. Calling testosterone hard on the heart was the old read. Actually, that is not quite right anymore. 

The better way to put it is that overall cardiac risk looked neutral, while a few specific events ticked up. The testosterone group had slightly higher rates of atrial fibrillation, acute kidney injury, and pulmonary embolism, a clot in the lung (Lincoff et al., 2023). On the strength of that trial and required blood pressure studies, the FDA dropped the old cardiovascular boxed warning in 2025 and added a blood pressure warning instead (FDA, 2025). The investigators stressed one point: these results apply to monitored men with confirmed low testosterone, not to high doses or to men without low levels.

Fertility and shrinking testicles

Testosterone from outside the body can switch off your own supply.

That can drop sperm production, sometimes to zero while you are on it, and shrink the testicles. For many men it reverses after stopping, but recovery can take months to over a year, and it is not guaranteed for everyone, especially with longer use or older age. The Endocrine Society recommends against TRT for men who want children in the near term (Bhasin et al., 2018). If fatherhood is anywhere on your radar, there are ways to protect fertility while on therapy. Raise it before you start, not after.

Prostate and PSA

The prostate fear is older than the current data.

A 2023 substudy of TRAVERSE tracked prostate outcomes in screened men and found no meaningful difference in high-grade prostate cancer between testosterone and placebo (Bhasin et al., 2023). The researchers were careful, though. The small number of cases means this does not prove the risk is identical, and the findings do not apply to men with known prostate cancer or a high PSA. Testosterone can still stimulate the prostate and may nudge PSA up, so PSA testing stays part of monitoring (Bhasin et al., 2018). Whether and how to monitor the prostate is a decision you and your provider make together, based on your age and risk.

Acne, gynecomastia, and fluid retention

These are the nuisance side effects. Annoying, rarely dangerous.

Some testosterone converts to estrogen, which can cause breast tenderness or swelling, called gynecomastia. Oily skin and acne are common in the first weeks. Mild fluid retention can puff up your ankles. A provider can usually settle these with a dose change or by managing how much testosterone converts to estrogen. None of them are reasons to panic. All of them are reasons to stay in contact with whoever wrote your prescription.

How do you lower your risk of TRT side effects?

The single best thing you can do is never start testosterone without baseline labs and a plan to recheck them.

1. Get a full baseline hormone panel first. Your provider confirms low testosterone with blood testing, usually on more than one morning, and checks for other risks before starting (Bhasin et al., 2018).

2. Recheck on a schedule. Your testosterone and blood counts early, then regularly, so a rising red blood cell count gets caught before it becomes a problem (Bhasin et al., 2018).

3. Match the form to your body. If your red blood cell count climbs fast on injections, a gel or a lower dose can help (Bhasin et al., 2018).

4. Confirm the reason. TRT is approved for low testosterone from a medical condition, not for normal aging (FDA, 2025).

5. Plan for fertility up front if you might want children.

The pattern in the data is hard to miss. When men are screened, dosed carefully, and checked on a schedule, most TRT side effects can be caught early and kept manageable. When testosterone gets handed out with no baseline labs and no follow-up, those same side effects can turn into real harm. When TRT goes badly, the story tends to rhyme: nobody was watching the bloodwork. A monitored testosterone plan backed by regular lab testing is the whole difference. So before you judge TRT side effects by a horror story online, ask whether that person had anyone checking their labs. That answer usually explains the rest.

Disclaimer: This blog post is intended for informational purposes only and should not be considered medical advice. Always consult a healthcare professional before making changes to your health routine.

FAQs

What are the most common TRT side effects?

The most common TRT side effects are acne, oily skin, fluid retention, breast tenderness, smaller testicles, and a lower sperm count. The one that needs the closest watch is a rise in red blood cells, since it can thicken the blood. Many are mild, but some can be serious, which is why monitoring matters.

Does TRT cause permanent infertility?

Usually not, but it can suppress sperm production while you take it, often down to zero. For many men this reverses after stopping, though recovery can take months to over a year and is not guaranteed. The Endocrine Society recommends against TRT for men who want children soon, so raise fertility plans before you start.

Is TRT bad for your heart?

The largest trial to date, TRAVERSE, found no increase in heart attack, stroke, or cardiac death versus placebo in older men with heart risk. The FDA removed the cardiovascular boxed warning from testosterone products in 2025. It was not all clear, though. Testosterone slightly raised rates of atrial fibrillation and blood clots, so monitoring still matters.

What hematocrit level is too high on TRT?

There is no single cutoff that fits everyone. Hematocrit measures how many red blood cells are in your blood, and your provider watches it on testosterone, acting if it climbs too high by lowering the dose, switching the form, or pausing therapy. A high level can thicken the blood and raise the risk of blood clots, which is why it is checked regularly.

How often do you need bloodwork on TRT?

Providers usually check your testosterone and blood counts soon after starting, then on a regular schedule. The goal is to catch any rising values before they become a problem. Skipping this follow-up is the most common reason TRT side effects turn serious.

Can you stop TRT once you start?

Yes, but your body has to restart the testosterone production it slowed while you were on therapy. That recovery can take time, and some men can feel low-testosterone symptoms again during the gap. Stopping should be planned with your provider, not done cold turkey.

Are TRT side effects worse with injections than gels?

Injections tend to raise red blood cells more than gels and can cause bigger swings between doses. Gels avoid those peaks but can transfer to other people through skin contact. The best form depends on how your body responds, which is one more reason monitoring matters.

References

• FDA. Class-wide labeling changes for testosterone products, 2025

• J Clin Endocrinol Metab. 2018;103(5):1715

• J Urol. 2018;200(2):423

• JAMA Intern Med. 2017;177(4):471

• JAMA Netw Open. 2023;6(12):e2348692

• N Engl J Med. 2016;374(7):611

• N Engl J Med. 2023;389(2):107