Risks and Side Effects
Testosterone is a well-understood medicine that millions of people take, cisgender men with low testosterone among them, and for most trans people the risks are modest and manageable. They are not zero, though, and most of them are the kind that show up in a blood test or a blood pressure reading long before they show up as symptoms. That is what the monitoring is for.
This page covers the side effects people notice, the risks prescribers are watching for, and the symptoms that should not wait for your next appointment. It is general information from the published guidance and from years of reading pre-surgery medication lists and blood results as a care coordinator. It is not medical advice, and I am not a doctor.
One rule runs through all of it: if something worries you, tell your prescriber rather than changing or stopping your dose yourself. Most of the fixes are adjustments they can make quickly.
On this page
Hematocrit and thick blood
Testosterone tells the body to make more red blood cells. That is a normal male effect, and it is the thing prescribers watch most closely. The measure is hematocrit (haematocrit in the UK), the share of your blood made up of red cells. When it climbs too high, called erythrocytosis or polycythemia, the blood gets thicker, and very high levels raise the risk of clots and strokes.
Guidelines differ on the exact line, but prescribers commonly start paying attention somewhere around 50 per cent and act if it goes higher, often by lowering the dose, shortening the injection interval so the peaks are smaller, or switching form. Smoking, sleep apnoea and living at altitude all push it up, and so do high peaks on fortnightly injections.
Most people never have a problem with it, and when it does rise it is usually easy to bring down. It is simply the number that tells you why the regular blood tests are not optional. Blood tests and monitoring explains the schedule.
Skin and hair
Acne is the most common side effect, especially in the first year or two, and often on the back and chest as well as the face. It usually improves as your body settles. Ordinary acne treatments work, and a GP or dermatologist can prescribe stronger ones if it is severe or scarring.
Scalp hair loss follows family patterns. If male-pattern baldness runs in your family, testosterone can bring it on. Some people accept it, some shave their head, and some ask about medication; a few of the medicines used for it can slow the development of body and facial hair, so that is a trade-off to talk through with your prescriber.
Heart, cholesterol and blood pressure
Testosterone tends to shift cholesterol in a less favourable direction: the "good" HDL cholesterol usually falls a little, and the "bad" LDL and triglycerides can rise. Blood pressure and weight can also go up. On their own these changes are usually modest, but they add to whatever risk you already have.
What we do not yet have is a clear picture of whether this adds up to more heart attacks and strokes over decades, because the long-term studies in trans men are still small. The sensible approach, and the one most prescribers take, is to keep an eye on blood pressure and cholesterol and to deal with the risks you can change: smoking above all, then weight, exercise and diet. Long-term health goes into this further.
If you smoke or vape
Tell your prescriber honestly, and treat stopping as part of your HRT. Smoking raises hematocrit, adds to clot and heart risk, and most surgeons will insist you stop before any operation anyway, so it is worth starting early.
Mood, energy and sleep
Many people feel better on testosterone, and relief at finally being on it is often the biggest mood change of all. Some notice irritability, a shorter fuse or a much stronger sex drive, especially in the first months and around the peaks of injections. These usually settle, and steadier dosing helps.
Testosterone can also make sleep apnoea more likely or worse, particularly alongside weight gain. Loud snoring, stopping breathing at night that a partner notices, and waking unrefreshed are worth mentioning.
Mood that gets markedly worse, or thoughts of harming yourself, need help promptly, from your GP, prescriber or a crisis line, whatever you think the cause is.
Pelvic pain and genital changes
Some people get cramping or pelvic pain on testosterone, even after periods stop. Often it is related to the womb adjusting, to troughs between doses, or to vaginal tissue thinning (atrophy), which can make sex and examinations uncomfortable. These are common and usually manageable; local vaginal estrogen is one option prescribers sometimes suggest for atrophy.
Pain that is new, severe, one-sided or keeps coming back should be checked, as would be true for anyone. Periods on testosterone covers bleeding, screening and atrophy in more detail.
Fertility
Testosterone can reduce fertility, and nobody can tell you in advance how much or whether it will come back if you stop. Many people have had biological children after stopping testosterone, and some have not. It is also not contraception: pregnancy on testosterone is possible and it can harm the pregnancy.
If having biological children might matter to you, the time to think about egg or embryo freezing is before you start. Fertility covers the options.
Symptoms that need help now
Contact a doctor or emergency services straight away for:
- Chest pain, sudden breathlessness or coughing up blood, which can be a clot in the lung
- A painful, swollen, hot calf or leg, which can be a DVT
- Sudden weakness or numbness on one side, a drooping face, slurred speech or a sudden severe headache, which can be a stroke
- Heavy bleeding, or severe pelvic or abdominal pain
- A hot, red, swollen, painful injection site, or fever after an injection
- Thoughts of harming yourself
These are rare. They are listed because knowing them means you act quickly if one does happen. Tell whoever sees you that you take testosterone.
Frequently asked questions
What are the most common side effects of testosterone?
Acne and oilier skin, increased appetite and libido, and in some people irritability or hair loss. Most settle or are manageable. See skin and hair and mood, energy and sleep.
What is hematocrit and why does it keep being tested?
It is the share of your blood that is red cells. Testosterone raises it, and too high makes the blood thicker, so prescribers check it regularly. See hematocrit and thick blood.
Is testosterone bad for your heart?
It shifts cholesterol and can raise blood pressure a little; whether that means more heart disease over decades is not yet clear. Not smoking matters more than almost anything else. See heart, cholesterol and blood pressure.
When should I get urgent help?
For chest pain, sudden breathlessness, a swollen painful leg, stroke signs, heavy bleeding or an infected injection site. See symptoms that need help now.