What is Testosterone Replacement Therapy?
TRT is a medical treatment designed to restore testosterone levels in men who have clinically low testosterone (hypogonadism). As men age, testosterone levels naturally decline by approximately 1-2% per year after age 30.
This gradual decline can lead to a range of symptoms that significantly impact daily life, including fatigue, decreased muscle mass, low libido, mood changes, and cognitive difficulties.
Low Testosterone in the UK
Low Testosterone in the UK
Far more common than most men realise — and far more treatable
Studies suggest around a quarter of men over 40 have testosterone levels below the healthy range.
The majority of men with low testosterone are never tested — symptoms are often dismissed as stress or ageing.
UK guidance requires two morning blood tests at least four weeks apart before treatment can be considered.
TRT is a well-established, evidence-based treatment prescribed under specialist medical supervision.
What Men Report on TRT
Findings from major peer-reviewed clinical trials of testosterone replacement therapy
Testosterone replacement therapy significantly improves sexual activity, desire and erectile function in men with confirmed low testosterone.
Source: Testosterone Trials, New England Journal of Medicine, 2016 (United States)
In men with type 2 diabetes or metabolic syndrome, testosterone replacement therapy reduced insulin resistance by approximately 15–16% and improved cholesterol levels over 6–12 months.
Source: TIMES2 Study, Diabetes Care, 2011 (UK/European multicentre trial, led by Sheffield researchers)
In men at risk of type 2 diabetes, adding testosterone treatment to a structured lifestyle programme reduced progression to type 2 diabetes by around 40% over two years, compared with the lifestyle programme alone.
Source: T4DM Trial, The Lancet Diabetes & Endocrinology, 2021 (Australia)
Testosterone replacement therapy consistently increases lean muscle mass and reduces fat mass — a finding replicated across multiple independent clinical trials.
Source: Multiple randomised controlled trials (multi-national)
A large-scale randomised trial found no increased risk of major cardiovascular events in men with hypogonadism treated with testosterone, providing reassurance on long-term safety.
Source: TRAVERSE Trial, New England Journal of Medicine, 2023 (United States)
The largest study of male ageing ever conducted, involving over 3,300 men across eight European countries including the UK, established that low testosterone reliably correlates with a specific triad of sexual symptoms — supporting the clinical case for testing when these symptoms are present.
Source: European Male Ageing Study (EMAS), multiple publications (UK/Europe)
Findings summarised from peer-reviewed clinical trials in men with confirmed low testosterone. TRT is prescribed only where clinically appropriate; individual results vary depending on your starting levels, treatment plan and lifestyle.
Who Should Consider TRT?
TRT may be right for you if you're experiencing symptoms of low testosterone and have been diagnosed with clinically low levels through blood testing. Total testosterone below 12 nmol/L is considered low under British Society for Sexual Medicine (BSSM) guidelines. Men with levels of 12–15 nmol/L and clear symptoms may still be candidates for treatment.
Common Symptoms:
- • Persistent fatigue and low energy
- • Decreased muscle mass and strength
- • Low libido and sexual dysfunction
- • Mood changes, irritability, or depression
- • Difficulty concentrating or "brain fog"
- • Increased body fat, especially around the midsection
Ideal Candidates
Risks & considerations
TRT is an effective treatment, but it is a medicine with real trade-offs. Here is what you should weigh up before starting.
Possible side effects
Acne, oily skin, mood changes, mild fluid retention and a raised red blood cell count (haematocrit) are the most commonly reported effects. These are monitored through regular blood tests and managed by adjusting your dose.
Fertility
Testosterone replacement therapy (TRT) suppresses your body's own testosterone production and can reduce sperm count while you are on treatment. If you are planning a family, tell your clinician — fertility-preserving alternatives such as clomiphene or hCG may be more appropriate.
It is a long-term commitment
For most men TRT is ongoing. Stopping abruptly can cause levels to fall quickly and symptoms to return, so any change should be planned with your clinician.
It isn't right for everyone
TRT is only prescribed where low testosterone is clinically confirmed. It is not prescribed for muscle building or athletic performance, and some medical histories make it unsuitable.
Monitoring is not optional
Ongoing blood tests and reviews are part of safe treatment. If you are unable to commit to monitoring, TRT is not appropriate for you.
More detail is set out in our frequently asked questions. Your clinician will go through all of this with you before prescribing.