TRT Side Effects: What to Know and How to Monitor Safely

The TRT patients I worry about most are not the ones who ask lots of questions about side effects. They are the ones who never ask at all, and who have never had a blood test since starting injections. Most side effects of TRT develop quietly, without warning symptoms. But if you are checked on schedule, nearly all of them can be picked up early and fixed.

Common side effects

Acne and oily skin

Testosterone stimulates the oil glands in the skin. This is usually noticed in the first few months, especially on the back and chest. It mostly settles once hormone levels become stable, or it can be treated with ordinary topical acne treatments (read hormonal acne).

Thickened blood (erythrocytosis)

This is the most important side effect on blood tests. It is more common with injections than with gel, particularly with types that cause a sharp peak in levels after each injection. If haematocrit rises above 54%, the doctor will pause treatment temporarily or reduce the dose, change the injection interval or switch the form of testosterone, and look for contributing causes such as obstructive sleep apnoea or smoking. Blood donation or therapeutic removal of blood (venesection) is used in some cases, as the doctor judges appropriate.

Smaller testes and reduced fertility

Testosterone from outside the body signals the brain to lower LH and FSH, so the testes stop making both their own testosterone and sperm. This happens to almost everyone on TRT. For most men it recovers after stopping, but recovery can take months to a year or more. If you still want children, plan this before you start (see semen analysis).

Male-pattern hair thinning

This happens in men who already carry the genes for hair thinning, because part of the testosterone is converted to DHT (see DHT and hair loss).

Breast enlargement or tenderness

This usually happens when testosterone levels are too high and more of it is converted to oestrogen. Adjusting the dose usually helps; routinely taking oestrogen-lowering tablets is not needed (read hormone imbalance in men).

Others

• Mild fluid retention and swelling
• Snoring or sleep apnoea getting worse
• Mood swings or irritability, usually when levels rise and fall a lot between injections
• Rash or skin irritation where gel is applied

Skin and hair

• Acne, oily skin
• Hair thinning if genetically prone

Blood

• Thickened blood (key lab concern)
• More common with injections than gel

Testes and fertility

• Smaller testes
• Lower sperm count, harder to conceive

Others

• Breast enlargement or tenderness
• Fluid retention, worse snoring
• Mood swings

Most develop quietly but are caught early and fixable if you attend follow-ups.

Heart, blood vessels and blood pressure: the latest data

There used to be concern that TRT increases heart attacks. The TRAVERSE trial (NEJM 2023), in 5,246 men at high cardiovascular risk, gave a much clearer answer.

On blood pressure, in 2025 the US FDA required all testosterone products to carry a warning that they may raise blood pressure, based on studies using 24-hour blood pressure monitoring. At the same time, it removed language about cardiovascular risk from the boxed warning. In practice, this means measuring your blood pressure at every follow-up visit, or checking it yourself at home. If you already have high blood pressure, it needs to be well controlled before and during treatment (read testosterone, blood pressure and diabetes).

No difference

• Heart attack, stroke, cardiac death
• High-grade prostate cancer (rare)

Slightly higher

• Atrial fibrillation (AF)
• Blood clot in the lungs
• Acute kidney injury
• Fractures 3.5% vs 2.5%

vs

TRAVERSE (NEJM 2023), 5,246 men. FDA (2025) required all products to warn about raised blood pressure.

The prostate

The fear that TRT causes prostate cancer comes from older data. Analyses from TRAVERSE found that high-grade prostate cancer, acute urinary retention and surgery for an enlarged prostate were uncommon and no different from placebo. However, the researchers excluded men at high risk or with a raised PSA from the start, so PSA should still be checked as appropriate for your age, and you should be referred to a urologist if PSA rises quickly or something abnormal is felt on examination.

Cholesterol and the liver

Injected or topical testosterone at replacement doses has only a small effect on blood lipids; it may lower HDL ("good" cholesterol) slightly. Liver problems are mostly seen with oral anabolic steroids used for bodybuilding, not with replacement testosterone used according to guidelines (see steroids and PEDs).

Risk to the people around you if you use gel

Gel that has not yet dried can transfer to a partner or a child. Children who are exposed repeatedly may show signs of early puberty, and women may develop acne or excess hair growth. To prevent this, apply the gel to the shoulders or upper arms, let it dry, wash your hands, and cover the area with clothing.

How to keep your risk as low as possible

1. Start only when the diagnosis is correct and there are no contraindications.
2. Use a dose that brings your hormone level to the middle of the normal range, not the top.
3. Have blood tests on schedule; what to test and when is covered in blood tests before and during TRT.
4. Treat other conditions too, such as high blood pressure and snoring, and stop smoking.
5. Do not buy testosterone yourself, do not raise the dose on your own, and do not add other substances without telling your doctor.

When to see a doctor, and how the clinic can help

Apart from the red flags above, book an appointment if you have frequent headaches, a flushed face, clearly worse acne, breast tenderness, difficulty passing urine, or snoring that is getting worse. At Dr. Kris Clinic, I look after men on TRT from the start through long-term follow-up, including men who started elsewhere and want someone to continue their care. English-speaking consultations are available in person in Surat Thani or online. If you have not started yet, you can read what TRT is and who it suits first.