How is low testosterone diagnosed in the UK?

By symptoms — such as persistent low libido, fatigue, mood changes and loss of morning erections — together with two morning blood tests showing low total testosterone on separate days. A single test is not sufficient, and treatable causes such as sleep apnoea and certain medications are screened for first.

Can I get TRT on the NHS?

Yes, when hypogonadism is properly confirmed. NHS pathways typically involve GP review with endocrinology input for diagnosis, then shared-care prescribing. Waiting times vary, which is why some patients choose a private route for the workup or initial phase.

How long does TRT take to work?

Libido and mood often improve within a few weeks, while changes in energy, body composition and haematocrit are typically reviewed at three to six months. Bone density changes are assessed over longer periods.

Does TRT affect fertility?

Yes. Exogenous testosterone suppresses the body's own testosterone production and can reduce sperm production, sometimes markedly. Men who want to preserve fertility should discuss alternatives with a clinician before starting.

Is TRT safe for the prostate?

Current UK monitoring includes PSA and prostate assessment before starting and at defined intervals. TRT is contraindicated in active prostate cancer. In appropriately selected men without prostate cancer, it is considered safe under monitoring.

Do I have to stay on TRT for life?

For men with primary or established secondary hypogonadism, TRT is typically long-term because the underlying cause does not reverse. Where a treatable cause is identified and corrected, TRT may sometimes be stopped after clinician-led reassessment.

Testosterone replacement therapy explained

TRT sits at an uncomfortable point in men's health: it is a legitimate, evidence-based treatment for a real condition, and it is also one of the most misused terms online. This article is written for men who suspect they may have low testosterone, or who have been offered TRT and want a clearer picture of what it involves. It walks through what testosterone does, what hypogonadism actually is, how it is diagnosed in the UK, the formulations used, what monitoring looks like, and the common concerns clinicians are asked about — fertility, prostate and red blood cells.

What testosterone does

Testosterone is the principal male sex hormone. Made mainly in the testes under signals from the pituitary and hypothalamus, it drives sexual development at puberty and continues to influence libido, erectile function, muscle mass, fat distribution, bone density, red blood cell production and mood throughout adult life. Levels naturally decline gradually with age — typically by around 1 to 2% per year from the 30s onwards — but this age-related decline is different from clinical hypogonadism.

What hypogonadism is — and isn't

Hypogonadism is the medical term for the body producing insufficient testosterone. It has two broad types. Primary hypogonadism is a problem with the testes themselves — for example, following certain infections, injury, chemotherapy or in genetic conditions such as Klinefelter syndrome. Secondary hypogonadism is a problem with the pituitary or hypothalamus signalling upstream — for example, in pituitary disorders, opioid use, obesity, chronic illness and untreated severe sleep apnoea.

Crucially, symptoms alone do not make the diagnosis. Fatigue, low libido, mood change, loss of morning erections, reduced muscle mass and increased body fat all have many possible causes. A proper workup separates men who have hypogonadism from men who have similar symptoms from another cause — because starting TRT in the wrong person adds risk without solving the underlying problem.

How diagnosis works in the UK

UK practice, in line with the British Society for Sexual Medicine and endocrinology guidance, is that hypogonadism requires symptoms plus confirmed low total testosterone on at least two separate morning blood tests. Testosterone follows a diurnal rhythm — highest in the early morning — so the sample timing matters. Samples taken in the afternoon or when acutely unwell are unreliable.

A workup typically includes total testosterone, sex hormone binding globulin (SHBG), calculated free testosterone, LH and FSH, prolactin, thyroid function, HbA1c and a full blood count. Prostate assessment with PSA is done as a baseline where appropriate. The clinician will also screen for treatable causes — significant obesity, poorly controlled diabetes, opioid use, untreated obstructive sleep apnoea — because addressing these sometimes restores testosterone without needing TRT. If low testosterone is confirmed after that workup, treatment can be discussed.

TRT formulations used in the UK

TRT is available in several forms. The choice depends on lifestyle, patient preference, side-effect profile and clinician judgement.

Transdermal gels

Applied daily to the shoulders, upper arms or abdomen, gels give steady blood levels and are easy to titrate. The main caveats are the need for daily application, care around skin-to-skin transfer to partners or children before the gel dries, and the need to shower before intimate contact. Products such as topical TRT gel are commonly used in UK men's health services.

Patches

Applied to non-genital skin, patches provide steady delivery but can cause skin irritation. They are less commonly used in current UK practice.

Intramuscular injections

Long-acting testosterone undecanoate injections are given every 10 to 14 weeks after loading doses, usually administered in a clinic. Shorter-acting testosterone enantate injections every 2 to 3 weeks are also used. Injections avoid daily dosing but produce peaks and troughs that can affect mood and energy in some men.

NHS and private pathways

Both routes exist in the UK. On the NHS, diagnosis typically starts with the GP, who arranges initial bloods and may refer to endocrinology for confirmation. Once diagnosed, prescribing often moves to shared care between the specialist and the GP. Waiting times and access can vary regionally, which is one reason some men use a private route for the workup or initial phase, then transition to shared care where possible. Whatever the route, the standards of diagnosis and monitoring should be the same.

Monitoring on treatment

Monitoring is not optional — it is a core part of safe TRT. UK guidance typically includes:

Symptom review and total testosterone at 3, 6 and 12 months, then annually.
Haematocrit and haemoglobin to detect polycythaemia — a rise in red blood cell concentration that can raise clot risk if unchecked.
PSA and prostate assessment at baseline and at intervals thereafter to monitor prostate health.
Lipid profile, HbA1c and blood pressure as part of broader cardiometabolic follow-up.

Dose is adjusted based on how the man feels and how his blood levels track. The goal is symptom improvement with levels in the mid-normal range, not levels artificially higher than normal.

Common concerns — fertility, prostate, red blood cells

Fertility

Exogenous testosterone suppresses the body's own testosterone production via feedback on the pituitary, which reduces sperm production, sometimes significantly. Men who want to father children in the near future should raise this before starting TRT. Alternatives exist that support fertility while addressing symptoms, and a clinician will advise based on your individual circumstances.

Prostate

TRT does not appear to cause prostate cancer in men who do not already have it, but it is contraindicated in active prostate cancer, and PSA monitoring is a standard part of follow-up. Men with significant urinary symptoms or a strong family history of prostate cancer should discuss this openly with their clinician.

Red blood cells (polycythaemia)

TRT can raise haematocrit. A moderate rise is expected; a significant rise raises the risk of blood clots and is one of the main reasons for regular blood monitoring. Dose reduction, switching formulation or occasional venesection are all responses used in practice.

Who should not have TRT

TRT is not appropriate in active prostate or male breast cancer, in men with a haematocrit above the accepted threshold at baseline, in untreated severe sleep apnoea, or in men actively trying to conceive without discussion of alternatives. Uncontrolled heart failure and recent major cardiovascular events are also reasons to defer or reconsider. A UK-registered clinician will screen for all of these at the initial assessment.

Men often ask about testosterone in the context of related concerns such as hair loss and sexual function. Our related articles on low testosterone and hair loss and erectile dysfunction go into these in more detail. In short, TRT is not a treatment for male-pattern hair loss and is not the first-line treatment for ED unless hypogonadism is confirmed as part of the picture.

Working with a Farmeci clinician

A Farmeci consultation for suspected low testosterone starts with a proper symptom review and, where appropriate, arranging morning bloods. If hypogonadism is confirmed after the full workup, treatment options are discussed alongside the monitoring plan, and the clinician will set expectations around what TRT does and doesn't do. If symptoms turn out to be driven by something other than low testosterone — stress, sleep, medication side effects, weight — the conversation shifts to addressing that instead. TRT is powerful when used in the right person; it is not a general wellness treatment.