Testosterone replacement therapy (TRT) is a medical treatment for men with confirmed hypogonadism, not a routine intervention based on age alone. The optimal timing for testosterone treatment depends on the underlying cause of deficiency rather than chronological age. In the UK, TRT is recommended only when persistently low testosterone levels are accompanied by relevant clinical symptoms such as reduced libido, erectile dysfunction, fatigue, or decreased muscle mass. This article explores when testosterone treatment is appropriate across different age groups, the diagnostic criteria used by NHS clinicians, and the benefits and risks associated with therapy at various life stages.

Understanding Testosterone Levels Across Different Ages

Testosterone is the primary male sex hormone responsible for developing and maintaining masculine characteristics, muscle mass, bone density, and sexual function. Throughout a man's life, testosterone levels naturally fluctuate, typically peaking during late adolescence and early adulthood before gradually declining from around age 30 onwards.

In healthy adult males, normal testosterone levels vary according to laboratory-specific reference ranges. The decline in testosterone with age is physiological, with total testosterone decreasing by approximately 1% per year after the age of 30, while free testosterone may decline more rapidly due to age-related increases in sex hormone-binding globulin (SHBG). This gradual reduction is distinct from pathological hypogonadism, where testosterone levels fall significantly below the normal range due to testicular, pituitary, or hypothalamic dysfunction.

It is important to distinguish between age-related testosterone decline (sometimes termed 'late-onset hypogonadism' or LOH) and true hypogonadism requiring treatment. Many men maintain adequate testosterone levels well into older age without experiencing symptoms. Factors such as obesity, chronic illness, medications, and lifestyle can significantly influence testosterone levels at any age.

Key points about testosterone across the lifespan:

• Testosterone production begins in utero and surges during puberty

• Peak levels occur between ages 20–30

• Gradual decline begins around age 30

• Significant inter-individual variation exists

• Low levels do not automatically warrant treatment

Understanding these natural variations is essential when considering whether testosterone treatment is appropriate, as age alone does not determine the need for therapy.

When Is Testosterone Treatment Recommended in the UK?

In the UK, testosterone replacement therapy (TRT) is recommended specifically for men with confirmed hypogonadism—a condition characterised by persistently low testosterone levels accompanied by relevant clinical symptoms. The Medicines and Healthcare products Regulatory Agency (MHRA) and professional guidelines emphasise that TRT should not be prescribed solely based on age or as an 'anti-ageing' intervention.

Diagnosis of hypogonadism requires both biochemical and clinical evidence. Biochemically, this means at least two separate morning blood tests (taken between 8–11 am when testosterone levels peak) showing total testosterone below the laboratory reference range. If total testosterone is borderline (typically 8–12 nmol/L), SHBG should be measured and free testosterone calculated to guide diagnosis. Clinically, men should experience symptoms such as reduced libido, erectile dysfunction, decreased energy, mood changes, reduced muscle mass, or increased body fat.

Additional tests should include luteinising hormone (LH), follicle-stimulating hormone (FSH) and prolactin to distinguish between primary and secondary hypogonadism and screen for pituitary disorders.

Conditions warranting testosterone treatment include:

• Primary hypogonadism: testicular failure due to genetic conditions (Klinefelter syndrome), chemotherapy, radiation, or trauma

• Secondary hypogonadism: pituitary or hypothalamic disorders affecting hormone signalling

• Congenital conditions: affecting testosterone production from birth or puberty

TRT is not recommended for men with normal testosterone levels experiencing non-specific symptoms like fatigue or low mood, as these are unlikely to improve with treatment. The NHS does not support testosterone therapy for age-related decline in otherwise healthy men, as there is insufficient evidence of benefit.

Before initiating treatment, comprehensive assessment including prostate examination, prostate-specific antigen (PSA) testing, full blood count, and cardiovascular risk evaluation is essential. Treatment is typically initiated by specialists (endocrinologists or urologists) with ongoing prescribing often managed through shared-care arrangements with GPs.

Age-Related Considerations for Starting Testosterone Therapy

The optimal age to commence testosterone therapy depends entirely on the underlying cause of hypogonadism rather than chronological age itself. However, different age groups present distinct clinical considerations that influence treatment decisions and monitoring requirements.

Younger men (under 40) with hypogonadism often have identifiable causes such as genetic conditions, pituitary tumours, or testicular damage. In this age group, TRT is typically more straightforward to justify, as testosterone deficiency significantly impacts quality of life, fertility, bone health, and metabolic function. However, fertility preservation is a critical consideration, as exogenous testosterone suppresses natural sperm production. Men wishing to father children may require specialist-led alternative treatments such as human chorionic gonadotrophin (hCG) or gonadotrophin therapy to stimulate endogenous testosterone and maintain fertility.

Red flag symptoms such as visual field defects, severe headaches, or raised prolactin levels warrant urgent endocrinology referral to exclude pituitary tumours.

Middle-aged men (40–60) represent the most common group seeking testosterone assessment. Distinguishing between pathological hypogonadism and age-related decline is crucial. Comprehensive evaluation of lifestyle factors—including obesity, sleep disorders (particularly obstructive sleep apnoea), diabetes, and medications—is essential, as addressing these may improve testosterone levels naturally without requiring TRT. Weight loss, improved sleep hygiene, and reduced alcohol consumption should be encouraged before considering TRT in borderline cases.

Older men (over 60) require particularly careful assessment. Whilst genuine hypogonadism can occur, age-related comorbidities increase treatment risks. Cardiovascular disease, prostate conditions, and polycythaemia (elevated red blood cell count) are more prevalent in this age group. NICE guidance emphasises thorough cardiovascular and prostate assessment before treatment initiation.

Regardless of age, treatment should only commence after specialist evaluation, with regular monitoring of testosterone levels, haematocrit, PSA, and symptom response. There is no single 'best age' for testosterone treatment—appropriateness depends on confirmed deficiency, symptom burden, and individual risk-benefit assessment.

Benefits and Risks of Testosterone Treatment by Age Group

Testosterone replacement therapy offers significant benefits for men with confirmed hypogonadism, but the risk-benefit profile varies across different age groups, necessitating individualised treatment decisions.

Benefits across age groups:

In younger men, TRT effectively restores libido, sexual function, energy levels, and mood whilst supporting bone mineral density and muscle mass development. These benefits are particularly important during formative years when testosterone deficiency can significantly impact psychological wellbeing and physical development.

Middle-aged men with genuine hypogonadism typically experience improvements in sexual function, body composition (increased lean muscle mass, reduced fat mass), bone density, and overall quality of life. Some studies suggest modest improvements in insulin sensitivity and metabolic parameters, though evidence remains mixed.

Older men may experience similar symptomatic benefits, though response rates can be more variable. Improvements in muscle strength and physical function may help maintain independence, but evidence for functional outcomes in this age group is inconsistent.

Risks and adverse effects:

Cardiovascular considerations: The MHRA has concluded there is no consistent evidence of an increased cardiovascular risk with TRT. However, caution is advised in men with severe cardiac, hepatic or renal disease, and it may be prudent to avoid initiating treatment soon after acute cardiovascular events.

Prostate-related risks include potential stimulation of pre-existing prostate cancer (though TRT does not cause prostate cancer) and benign prostatic hyperplasia progression. Regular PSA monitoring and digital rectal examination are recommended according to shared-care protocols, with treatment contraindicated in men with prostate cancer.

Haematological effects: Testosterone stimulates red blood cell production, potentially causing polycythaemia (haematocrit >0.54), which increases thrombotic risk. If this occurs, dose reduction, temporary treatment pause, or venesection may be required.

Other considerations include acne, fluid retention, testicular atrophy, and suppression of natural testosterone production. In younger men, fertility suppression is a significant concern requiring careful counselling.

Transdermal gel safety: Men using testosterone gel must wash hands after application, allow the gel to dry completely, and cover the application site to prevent transfer to women or children through skin contact.

The risk-benefit balance is generally most favourable in younger men with clear-cut hypogonadism and least favourable in older men with borderline testosterone levels and multiple comorbidities.

NHS Guidelines on Testosterone Replacement Therapy

The NHS follows guidance from NICE, the British Society for Sexual Medicine (BSSM), and the European Academy of Andrology regarding testosterone replacement therapy. These guidelines emphasise evidence-based practice and patient safety.

Diagnostic criteria require biochemical confirmation with two early-morning testosterone measurements showing levels below the laboratory reference range, accompanied by consistent clinical symptoms. If total testosterone is borderline or SHBG is abnormal, free testosterone should be calculated. Baseline LH, FSH and prolactin should be measured to determine the type of hypogonadism and screen for pituitary disorders.

Prescribing pathway: TRT is typically initiated by specialists (endocrinologists or urologists) following comprehensive assessment. GPs may continue prescribing under shared care arrangements once treatment is established and stable.

Monitoring requirements include:

• Testosterone levels at 3-6 months, then annually

• Haematocrit/full blood count at 3-6 months, then annually

• PSA and digital rectal examination before treatment and periodically based on age and risk factors

• Bone density assessment in men with osteoporosis risk

• Symptom review and treatment response evaluation

Contraindications to TRT include:

• Prostate or male breast cancer (absolute contraindications)

• Desire for fertility in the near term (relative contraindication)

Cautions include:

• Severe cardiac, hepatic or renal disease

• Untreated obstructive sleep apnoea

• Polycythaemia (haematocrit >0.54)

Treatment formulations available on NHS prescription include transdermal gels (most commonly prescribed) and intramuscular injections (such as Nebido or Sustanon). Choice depends on patient preference, tolerability, and ability to maintain stable testosterone levels.

When to seek medical advice: Patients on TRT should contact their GP if they experience chest pain, breathing difficulties, leg swelling, urinary symptoms, or mood changes. Regular monitoring appointments should not be missed.

Patients should report any suspected side effects via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

The NHS does not support testosterone therapy for age-related decline without confirmed hypogonadism, lifestyle optimisation for weight loss and exercise, or performance enhancement purposes. Treatment decisions should always be individualised, evidence-based, and made in partnership between clinician and patient.

Frequently Asked Questions