Confession time. When a man asks me "is TRT safe?", my honest answer is "it depends", and I know that's the single most irritating thing a doctor can say. So I thought I'd write down what it actually depends on: what the big trials found, which risks are real, which ones have mostly been put to bed, and who I'd tell not to start at all.
This one's a long one, because the question deserves more than a yes or no.
So, is TRT safe? It depends on three things
Here's the thing. TRT is a medicine, and like any medicine, how safe it is depends on who's taking it, what they're taking, and who's watching.
- The right man. Someone with symptoms and testosterone that's genuinely low on proper blood tests, not someone with normal levels who wants to feel 25 again.
- The right medicine. Pharmaceutical testosterone, prescribed by a doctor and dispensed by a registered pharmacy, at a dose aimed at getting you back into the normal range. Not beyond it.
- The right monitoring. Regular bloods, read by a doctor, with someone who acts when a number goes the wrong way.
Get all three and, in men with confirmed low testosterone, the evidence says TRT is a safe treatment. Take any one of them away and my answer changes quite quickly.
On that first point, the British Society for Sexual Medicine (BSSM) wants two early morning blood tests before anyone is diagnosed, because testosterone bounces around and one low reading on a rough week isn't a diagnosis. I won't start anyone on one test. If you're wondering whether your numbers count as low, my guide to normal testosterone levels will help.
The big scary one: your heart
If you've read anything about TRT, you've probably read that it causes heart attacks. I understand why. Around 2010 a small trial in older men with limited mobility was stopped early because more of the men on testosterone had heart problems, and a couple of large observational studies in 2013 and 2014 pointed the same way. The headlines wrote themselves.
Those studies had real weaknesses, though, and the American regulator, the FDA, told the manufacturers to run a proper trial. That trial was TRAVERSE, published in the New England Journal of Medicine in 2023, and frankly it's the most useful thing to happen to this conversation in years.
TRAVERSE took 5,246 men aged 45 to 80 with low testosterone and symptoms, all of whom either already had heart disease or were at high risk of it. Half got testosterone gel and half got a placebo gel, and they were followed for an average of nearly three years. The rate of heart attacks, strokes and deaths from heart disease was no higher in the testosterone group.
That's reassuring, and in exactly the men we were most worried about. But the trial wasn't spotless. The testosterone group had more atrial fibrillation (an irregular heart rhythm), more acute kidney injury and more pulmonary embolism (a clot on the lung). The numbers were small, but they were there, and anyone who tells you TRAVERSE proved TRT is risk-free hasn't read it properly.
Here's a nerdy one. TRAVERSE was a "non-inferiority" trial. In plain English, it was designed to show testosterone isn't worse for your heart than placebo, not that it's better. So if someone tells you TRT protects your heart, that's a step further than the evidence goes.
Prostate: the worry that's mostly moved on
The old teaching was that testosterone feeds prostate cancer, so giving it was like pouring petrol on a fire. That idea has largely been retired. A separate analysis of the TRAVERSE men, published in JAMA Network Open in 2023, found high-grade prostate cancer was rare in both groups and not significantly more common with testosterone.
That doesn't mean we stop checking. PSA (a blood marker for prostate activity) usually creeps up a little when testosterone comes back to normal, and a small rise is expected. A big or sustained rise needs looking at properly, with a referral if it's warranted.
One example I come across that genuinely worries me: a significantly raised PSA that wasn't acted on, because the patient was contacted through an app rather than by an actual medical professional. That's not a testosterone problem. It's a monitoring problem.
The one that actually keeps me busy: thicker blood
If you asked me which side effect I spend the most time managing, it isn't the heart or the prostate. It's haematocrit.
Haematocrit is the proportion of your blood made up of red blood cells. Testosterone tells your bone marrow to make more of them, which is partly why some men feel more energetic on it, but push it too far and your blood gets thicker. The worry with thick blood is clots, which is why it gets watched closely.
The Endocrine Society guideline says not to start TRT if your haematocrit is already raised, and to stop or adjust treatment if it goes above 54 percent. In real life a haematocrit drifting up by the three-month bloods is very ordinary, especially on injections. It's usually fixed by adjusting the dose or the timing, occasionally by giving blood. What matters is that somebody spots the trend early.
Fertility, which nobody mentions in the adverts
This is the one I'd most like every man to know about before he starts, rather than after.
When you take testosterone, your brain notices there's plenty about and turns down the signals (LH and FSH) that tell your testicles to make their own, and to make sperm. So TRT can lower your sperm count a lot, sometimes to zero.
For most men this recovers after stopping, but it can take many months, and it isn't guaranteed. It's also not reliable contraception, so please don't treat it as such. If you're planning a family, or might one day, there are medicines such as HCG that help protect fertility on TRT, and that's a conversation for your first consultation. I've written about it in much more detail in TRT and fertility.
The annoying ones, and the two I take seriously
Some side effects are a nuisance rather than a danger: oily skin, acne on the back and shoulders, a bit of fluid retention, occasionally tender nipples when oestrogen rises. They're common early on and usually settle, sometimes with a tweak to the dose or interval. I've gone through these one by one in my post on TRT side effects.
Two others I don't treat as a nuisance:
- Sleep apnoea. Testosterone can make obstructive sleep apnoea (where your airway keeps closing while you sleep) worse. If your partner has been nudging you for snoring and gaps in your breathing, tell your doctor before you start, not after.
- Blood pressure. It can nudge up on treatment, so it should be checked at the start and along the way. Boring, I know. Still matters.
Who I'd tell not to start (or not yet)
A good clinic says no fairly often. These are the situations where the BSSM and Endocrine Society guidelines say TRT shouldn't be started, or should wait until something else is sorted first:
- Active prostate cancer or breast cancer.
- Wanting to have a baby in the near future, unless fertility is being protected properly.
- A haematocrit that's already high before treatment.
- Untreated severe sleep apnoea.
- A heart attack or stroke in the last six months, or heart failure that isn't under control.
- Testosterone that isn't actually low. Normal levels plus tiredness usually means the tiredness is coming from somewhere else.
That last one is where I'm least popular. Tiredness can be your thyroid, your iron, your sleep, your mood, or something more serious, and testosterone won't fix any of those. On the other hand, I see the opposite problem all the time: a man with a testosterone level between 8 and 12 nmol/L and every symptom on the list of low testosterone symptoms, told by his GP that he's "within range". The BSSM guideline would consider treating a lot of those men.
And if you've got a lot of other medical things going on, you may honestly be better off being looked after face to face. A clinic that tells you that, even when it costs them your business, is one I'd trust.
Where it really goes wrong: testosterone from the gym
Most of the really frightening testosterone stories you read have nothing to do with prescribed TRT. They're about stuff bought online or from a bloke at the gym.
Testosterone is a Class C controlled drug in the UK. On prescription it's completely legal. Buying it without one isn't. And legality is the least of the problems: you don't know what's in the vial, you don't know the dose, it's often taken at many times a replacement dose, and nobody is checking your blood count, your PSA or your blood pressure. Every risk above gets bigger, with nobody watching.
If you're already doing this and want to come off it safely or move onto a proper prescription, please talk to a doctor. You won't get a lecture from me, just a plan.
So what does safe TRT actually look like?
Right, enough of the risks. If you're choosing a clinic, this is the checklist I'd use.
- Proper diagnosis. Two early morning blood tests, plus a baseline full blood count, PSA and the other basics, before anything is prescribed. A testosterone blood test is where it starts.
- A fertility conversation before you begin. Not buried in the terms and conditions.
- Regular bloods once you're on it. With us that's six weeks, then every three to six months.
- A doctor reading every result. Not just the ones a computer flags.
- A phone call for anything serious. The same day, from a real person.
That last one isn't me being dramatic. Another real example: a prolactin of 15,000 that was sent to the patient as a message in an app. For context, that's wildly high, the kind of number that can point to a problem with the pituitary gland and needs urgent investigation. It should have been a phone call that afternoon.
If your current clinic doesn't do these things, you can switch your TRT to us and bring your existing bloods with you.
The bottom line
Is TRT safe? In a man with properly confirmed low testosterone, on prescribed medication, with a doctor reading his bloods, yes, I think it is. Not risk-free, but safe, and TRAVERSE gives us better evidence for that than we've ever had.
The risks that matter most are the ones nobody's looking for. So get tested properly, ask who reads your results and how often, have the fertility conversation before you start, and don't buy it from the gym. If you'd like us to look at your symptoms and numbers, get started here.
That's the honest version. If it's raised more questions than it answered, that's what the first consultation is for.
Dr Chris Airey
Sources: Lincoff AM et al, Cardiovascular Safety of Testosterone-Replacement Therapy (the TRAVERSE trial), New England Journal of Medicine, 2023. Bhasin S et al, Prostate Safety Events During Testosterone Replacement Therapy in Men With Hypogonadism, JAMA Network Open, 2023. Basaria S et al, Adverse Events Associated with Testosterone Administration, New England Journal of Medicine, 2010. Hackett G et al, The British Society for Sexual Medicine Guidelines on Male Adult Testosterone Deficiency, with Statements for Practice, World Journal of Men's Health, 2023. Bhasin S et al, Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology and Metabolism, 2018.
Keep reading
For the complete picture, see my full guide to TRT in the UK, covering eligibility, blood test thresholds, NHS and private routes, costs and monitoring. If the heart and prostate stories are what put you off, TRT myths and facts takes the rest of the scare stories one at a time.
