Testosterone replacement therapy (TRT) does what it says on the tin: it tops up low T levels to help with symptoms like low libido and energy. It’s a synthetic version of the hormone that you can take as a gel, tablet or injection.
Like any medicine, TRT comes with side effects—yet most of the time, they’re manageable. Here’s what you need to know.
What are the side effects of TRT?
These can vary depending on the type of TRT you’re on, the dose and your medical history.
Common side effects of TRT
Most men either have no side effects or only mild, short-lived ones. When side effects do occur, they are usually easy to manage with routine monitoring and dose or formulation adjustments.
Reported side effects include:
- Acne or oiler skin
- Nipple sensitivity or enlarged breast tissue (gynecomastia)
- A rise in red blood cells that can thicken the blood (erythrocytosis)
- Fluid retention
- Tiredness
- Reduced fertility due to suppression of sperm production
At MANUAL, your clinician follows a structured monitoring plan from the start, with regular blood tests and check-ins. We adjust or pause therapy if needed and proactively manage dose, formulation, and any oestrogen-related symptoms before they become problems. This approach means most men avoid long-term issues and get the benefits of TRT with confidence.
Expert insights from Jeff Foster on TRT safety
"Many patients worry about side effects, or potential side effects with TRT, and while we have to list all side effects, the vast majority of men experience very little or none. The key point is that virtually all side effects can be managed or mitigated for by speaking to your doctor.
The overwhelming evidence is that TRT remains a safe and effective treatment for the majority of men."
Medical Director Jeff Foster - Men’s Health & TRT Specialist
More serious or long-term side effects of TRT
While less common, some side effects of TRT are more significant and may only appear after longer use. These require careful monitoring and regular blood tests to ensure treatment stays safe.
So when you’re choosing your TRT provider, make sure regular blood tests are included in your treatment plan. TRT at MANUAL starts at just £99 per month and all monitoring blood tests (and any necessary clinic visits) are covered. After each blood test, you’ll receive direct feedback from your doctor.
Blood clots and heart problems
For decades there has been debate about whether TRT increases major heart events in older men. TRT can raise your red blood cell count a little, which thickens the blood. Early studies hinted this might raise the risk of clots or heart problems, but results were mixed and the first randomized trials were too small to settle it.
The largest study so far, TRAVERSE, tracked thousands of men on receiving TRT or placebo for 33 months (about 3 years). Heart attacks, strokes, or cardiovascular deaths occurred in 7.0% on TRT versus 7.3% on placebo, which met noninferiority. In other words, TRT did not increase major cardiovascular events compared with placebo.
The key is regular monitoring and working with your clinician while you are on TRT — which is why being with a specialist service like MANUAL makes such a difference.
Prostate health
Testosterone therapy can nudge your prostate, that little walnut-shaped gland below your bladder, to grow. An enlarged prostate isn’t serious, though it can make peeing difficult for some men. In clinical studies, men on TRT did not have more urinary problems than those on placebo.
Your PSA may rise while you are on TRT. People often associate a higher PSA with cancer, but this rise is expected with TRT because the prostate is returning toward its usual size for your age as testosterone is restored to normal. It does not mean cancer is being fuelled. In fact, recent high-quality evidence, including the large TRAVERSE trial, found no increase in prostate-cancer risk with TRT compared with placebo. At MANUAL, we will still check PSA and urinary symptoms regularly to keep you safe.
Sleep apnoea
There’s a link between sleep apnoea, where your breathing stops and starts while you sleep, and TRT. But it’s not well understood. Some studies show that T therapy increases the risk of sleep apnoea but others suggest the opposite.
Fertility on TRT: what to expect and how to preserve it
So, does TRT affect fertility? Yes, it can. When you take synthetic testosterone, it can reduce the amount your body makes naturally. That may mean you make less sperm.
If you stop taking TRT, this effect is usually reversible—though it may take a number of months for your fertility to return.
But you have other options here. One is to take human chorionic gonadotropic (hCG) treatment alongside TRT, which works to simulate sperm production.
Not everyone who takes TRT will notice fertility changes, but it’s important to be aware of the possibility and discuss preservation options before starting therapy.
How to reduce the risk of side effects of TRT?
When you start on TRT, your provider will regularly run tests to monitor how you’re responding to the medicine. This helps pick up small changes early so they can be addressed quickly.
For example, it’s recommended to check red blood cell count and testosterone around the 3, 6, and 12-month points after starting, then every 6 months thereafter. Timing may vary by formulation, but the principle is the same: steady, structured monitoring. Most people find the 6-monthly check-ins genuinely useful beyond TRT. They provide a regular health MOT, keeping an eye on things like blood pressure, blood counts, and PSA, and making sure your treatment stays safe and effective.
If you are getting side effects, your provider may suggest adjusting your dose or switching to a different type of TRT. You also might benefit from making lifestyle changes. For instance, losing weight and stopping smoking may reduce your risk of blood clots.
Heads up: make sure you’re working with a qualified clinician and getting your TRT from a registered pharmacy or clinic. This information should be on their website.
What to do if you notice side effects on TRT
If something feels off, tell your clinician. Most issues are easy to fix with simple tweaks. Your clinician may adjust your dose, switch you to a different formulation, change application timing, or treat the specific issue such as fluid retention or acne. They may also arrange blood tests to check hormone levels and safety markers.
It can also help to keep a brief log of what you feel, when it happens, and how it relates to your dose or application so patterns are easy to spot.
Some mild symptoms can improve with over-the-counter options and lifestyle changes, but don’t stop or change your TRT on your own — speak to your clinician first.
Medicines to tell your clinician about before starting TRT
TRT is generally safe alongside nearly all medicines. Some medicines just mean your clinician may monitor you a bit more closely or adjust doses. Tell your clinician if you use:
- Blood thinners (for example, warfarin): You may need extra clotting checks when starting or changing TRT.
- Diabetes medicines (insulin, gliclazide, metformin): TRT can improve insulin sensitivity, so doses sometimes need adjusting to avoid low blood sugar.
- Epilepsy or certain sleep medicines: Examples include carbamazepine, phenytoin, and phenobarbital. These can make your body clear testosterone faster, so your TRT dose or blood-test timing may change.
This isn’t a full list. Always share everything you take — prescriptions, over-the-counter products, vitamins, herbal remedies, and gym or online supplements — so your clinician can plan any extra monitoring and keep treatment safe and effective.
Who shouldn’t take TRT?
TRT is safe for the vast majority of patients but TRT isn’t right for everyone. That’s why your doctor will evaluate your current health and medical history, as well as the results of any tests they run, when deciding whether to prescribe it to you.
In general, TRT is not recommended or may be delayed if you have:
- Active prostate or male breast cancer (known or suspected)
- History of liver tumours.
- Unexplained high PSA or abnormal prostate exam pending urology review.
- Very high red blood cell count
- Hypersensitivity to testosterone or any ingredient in the product.
- Severe, uncontrolled conditions that need stabilising first, such as advanced heart failure, untreated severe sleep apnoea, or serious kidney or liver impairment.
- Plans for near-term fertility (TRT can suppress sperm production; alternatives may be more appropriate).
Note: This isn’t a complete list. Decisions are individual and based on your history, exam, and labs. If any of the above apply, your clinician will discuss options and timing.
Could TRT be a good fit for you?
Wondering if low testosterone is holding you back? Boost your energy, drive and strength with a tailored testosterone plan built by leading TRT doctors.
Order a quick finger-prick blood test today to see if TRT could help you feel your best again.
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