Testosterone replacement therapy: who it suits and who it doesn’t

1What is testosterone replacement therapy and who is it for?

Testosterone replacement therapy (TRT) gives testosterone to a man shown not to make enough, a condition called hypogonadism or low testosterone. According to the Endocrine Society clinical practice guideline, diagnosis needs both symptoms that fit deficiency and consistently low blood levels.

Symptoms the sources describe include:

• Low sex drive, fewer morning erections or difficulty getting an erection.
• Ongoing tiredness, poor concentration or memory, and low mood.
• Loss of muscle mass and strength, and more body fat.
• Less underarm and pubic hair, smaller testicles and enlarged breast tissue.

A King’s College Hospital NHS leaflet notes that these symptoms can have other causes, so a medical assessment comes first, not a trial of hormones.

🔬How is low testosterone diagnosed before treatment?

Diagnosis combines symptoms, an examination and timed blood tests, as levels are highest in the morning:

• Repeated morning tests: according to the European Association of Urology (EAU) 2025 pocket guidelines, total testosterone should be measured in the morning, between 7 and 11 o’clock, while fasting, and repeated on at least two separate occasions before any treatment. The EAU uses 12 nmol/L (3.5 ng/mL) as the threshold for diagnosing late-onset hypogonadism, while Cleveland Clinic says a level below 300 ng/dL is considered low in adults; cut-offs and units differ between guidelines and laboratories, so your doctor interprets the result. Cleveland Clinic also notes that illness can lower levels temporarily.
• Finding the cause: the Endocrine Society recommends measuring the pituitary hormones LH and FSH to tell testicular problems from pituitary problems, then looking for the underlying cause.
• Blood and prostate: haematocrit (red cell proportion) and prostate risk, including a PSA test, are usually assessed before starting.

3Who should not have testosterone therapy?

According to the Endocrine Society guideline, treatment should not be started in men with:

• Plans to father a child in the near future.
• Breast or prostate cancer, or a lump or hardening in the prostate on examination.
• A PSA above 4 ng/mL that has not been assessed by a urologist.
• A raised haematocrit (thick blood).
• Untreated severe obstructive sleep apnoea, or severe urinary symptoms.
• Uncontrolled heart failure, or a heart attack or stroke within the last 6 months.
• An inherited tendency to blood clots (thrombophilia).

The EAU adds that family history of vein clots and heart risk factors should be checked first; Cleveland Clinic also lists poorly controlled blood pressure.

💊Forms of testosterone treatment

The NHS says treatment may be given as an injection or a gel. The doctor chooses the form with you; the sources describe these pros and cons:

👶Testosterone and fertility: important if you want children

According to a 2025 review in Translational Andrology and Urology, testosterone from outside the body makes the pituitary lower LH and FSH, so testosterone inside the testicles falls and sperm production is suppressed. The review cites a study in which about two-thirds of men regained a normal sperm concentration within six months of stopping, while some needed up to 2 years; full recovery is not guaranteed, and older age and longer use are linked to delayed or incomplete recovery.

The same review quotes the American Urological Association (AUA) position that testosterone should not be prescribed to men who are currently trying to conceive, and the EAU states that testosterone should not be used to treat male infertility. If you are planning a family, tell your doctor before starting so other options can be discussed.

6Monitoring and possible side effects

According to the EAU, haematocrit and testosterone levels should be checked at 3, 6 and 12 months after starting and then every year, and a haematocrit above 54% means treatment must be adjusted or stopped. For men in the age groups where prostate monitoring applies, the Endocrine Society recommends assessing prostate cancer risk before starting and 3 to 12 months after starting, with referral to a urologist if PSA rises by more than 1.4 ng/mL in the first year or goes above 4 ng/mL. The King’s College Hospital leaflet says PSA checks matter especially in men over 45.

Side effects listed in that leaflet include:

• Thicker blood, which may raise the risk of heart attack, stroke and blood clots.
• Prostate enlargement or other prostate problems.
• Acne, excessive sweating, hot flushes, weight gain and increased appetite.
• Mood changes such as irritability, low mood or restlessness.

Do not change or stop treatment on your own.

💡Common myths about testosterone

• “Every ageing man needs testosterone”: according to the NHS, testosterone falls by about 1% a year from around age 30 to 40, which alone is unlikely to cause problems.
• “It restores youth and helps weight loss”: the EAU does not recommend it for vitality or strength in ageing men, weight loss, or men with normal levels.
• “It is a safe way to build muscle”: the NHS says misusing anabolic steroids can cause reduced sperm count, infertility, shrunken testicles and breast development in men, as well as heart attack and stroke.

🚑When to see a doctor, and when it is an emergency

See a urologist or endocrinologist if you have a lasting drop in sex drive or erections, unexplained tiredness or low mood, or smaller testicles, or if you are using hormones without medical supervision. You can read more about men’s health.

On treatment, seek emergency care for chest pain, sudden breathlessness, sudden one-sided weakness or trouble speaking, or a painful swollen leg, as thicker blood raises clot risk. Tell your doctor promptly about urinary difficulty, severe mood changes, or plans to try for a baby.

❓Frequently asked questions

10Sources

1. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline
2. EAU Pocket on Sexual and Reproductive Health 2025 (European Association of Urology)
3. The 'male menopause' – NHS
4. Testosterone replacement therapy – King's College Hospital NHS Foundation Trust (patient leaflet)
5. Low Testosterone (Male Hypogonadism) – Cleveland Clinic
6. Preserving spermatogenesis in testosterone deficiency: innovations in replacement and stimulatory therapies – Translational Andrology and Urology (2025)
7. Anabolic steroid misuse – NHS