Many individuals wonder whether 18 is too late to begin testosterone treatment, particularly those experiencing delayed puberty, hypogonadism, or gender dysphoria. The answer is clear: 18 is not too late. Testosterone therapy can be safely and effectively initiated at this age or later, following proper medical assessment by qualified healthcare professionals. Whether for confirmed hypogonadism (insufficient testosterone production) or as part of gender-affirming care for transgender men and non-binary individuals, treatment at 18 offers significant physical and psychological benefits. In the UK, testosterone is a prescription-only medicine regulated by the MHRA, requiring specialist evaluation, informed consent, and ongoing monitoring to ensure safe and appropriate use.

Understanding Testosterone Treatment at 18

Eighteen is not too late for testosterone treatment — in fact, many individuals commence therapy at this age or later following proper medical assessment. Testosterone therapy may be clinically indicated for various conditions, including hypogonadism (insufficient testosterone production), delayed puberty, or as part of gender-affirming care for transgender men and non-binary individuals assigned female at birth.

Testosterone is a naturally occurring androgen hormone primarily produced in the testes in males and in smaller amounts in the ovaries and adrenal glands in females. It plays crucial roles in developing secondary sexual characteristics, maintaining muscle mass and bone density, regulating mood, and supporting reproductive function. When endogenous testosterone production is insufficient or absent, replacement therapy may be medically indicated.

The timing of testosterone initiation depends entirely on the underlying condition and individual circumstances. For cisgender males with constitutional delay of growth and puberty, treatment may have begun earlier under specialist supervision. However, many individuals are not diagnosed with hypogonadism until late adolescence or adulthood. Regarding consent in the UK: young people aged 16–17 years who have capacity can usually consent to medical treatment, including hormone therapy, without parental involvement. Those under 16 may be able to consent if they are assessed as Gillick competent. At 18, individuals have full legal capacity as adults. Transgender individuals seeking gender-affirming hormone therapy require assessment by specialist gender identity services regardless of age.

It is essential to understand that testosterone therapy is a prescription-only medicine in the UK, regulated by the Medicines and Healthcare products Regulatory Agency (MHRA). Treatment is indicated only for specific clinical conditions — it is not appropriate for performance enhancement or normal ageing. Therapy must be initiated and monitored by qualified healthcare professionals, typically endocrinologists or specialists in gender identity services, following comprehensive assessment and informed consent discussions.

When Testosterone Therapy Is Recommended

Testosterone replacement therapy is clinically indicated when there is biochemically confirmed hypogonadism — persistently low serum testosterone levels accompanied by symptoms. According to guidance from the British Society for Sexual Medicine (BSSM) and UK endocrinology specialists, diagnosis requires at least two early-morning testosterone measurements (taken before 11:00 AM when levels are typically highest) showing results below the normal reference range, typically below 8–12 nmol/L depending on the laboratory. When sex hormone-binding globulin (SHBG) is abnormal or total testosterone is borderline, free or bioavailable testosterone should be calculated or measured to confirm the diagnosis.

Common clinical scenarios warranting testosterone therapy include:

• Primary hypogonadism — testicular failure due to genetic conditions (such as Klinefelter syndrome), chemotherapy, radiation, trauma, or infection

• Secondary hypogonadism — pituitary or hypothalamic disorders affecting luteinising hormone (LH) and follicle-stimulating hormone (FSH) production

• Constitutional delay of growth and puberty — when puberty has not commenced by age 14 or remains incomplete by late adolescence

• Gender dysphoria — as part of gender-affirming hormone therapy for transgender men and non-binary individuals, following assessment by specialist gender identity clinics

Before initiating treatment, clinicians must exclude contraindications and investigate underlying causes. Baseline investigations typically include: two timed total testosterone measurements, SHBG, LH, FSH, prolactin, full blood count, liver function tests, lipid profile, thyroid function, and iron studies. Prostate-specific antigen (PSA) testing is not routinely required in young adults without risk factors or symptoms; it is typically reserved for men over 40 years or those with specific risk factors, following shared decision-making. Bone density assessment (DEXA scan) should be targeted to individuals with prolonged hypogonadism or other osteoporosis risk factors. If secondary hypogonadism is suspected, pituitary imaging may be indicated.

Absolute contraindications to testosterone therapy include prostate cancer, male breast cancer, and polycythaemia. Relative contraindications and cautions include severe hepatic impairment, uncontrolled heart failure, and untreated severe obstructive sleep apnoea; these conditions require optimisation and careful monitoring if treatment proceeds.

The decision to commence testosterone therapy should follow thorough discussion of benefits, risks, and alternatives. Fertility counselling is essential: exogenous testosterone suppresses spermatogenesis and is not a treatment for male infertility. Individuals wishing to preserve fertility should be offered sperm banking before starting therapy. For those with the potential to become pregnant, contraception advice and pregnancy testing (if uncertainty exists) are necessary, as testosterone is teratogenic and amenorrhoea induced by testosterone does not guarantee contraception.

Benefits of Starting Testosterone Treatment at 18

Commencing testosterone therapy at 18 offers several potential advantages, particularly regarding physical development and psychological wellbeing, when clinically indicated.

Physical benefits of testosterone therapy include:

• Development of secondary sexual characteristics — deepening of voice (irreversible), facial and body hair growth (largely irreversible), increased muscle mass, and redistribution of body fat to a more typically masculine pattern

• Improved bone mineral density — testosterone is crucial for achieving peak bone mass, which typically occurs in the early to mid-twenties; adequate testosterone during this period helps prevent osteoporosis later in life

• Enhanced muscle strength and physical performance — testosterone promotes protein synthesis and muscle development, supporting physical fitness and metabolic health

• Genital development — in cases of delayed puberty, testosterone supports penile growth; testicular growth may be limited in secondary hypogonadism

Regarding height: once growth plates have fused (which typically occurs by late adolescence), further height gain is not expected. In constitutional delay of growth and puberty, specialist endocrinologists may use carefully timed testosterone dosing to initiate puberty whilst aiming to preserve final height potential, but net height gain at 18 is uncertain and not guaranteed.

Psychological and quality-of-life benefits are equally significant. Many individuals with untreated hypogonadism experience low mood, reduced energy, poor concentration, and diminished self-confidence. Testosterone therapy often improves mood, energy, and libido in those with confirmed hypogonadism. For transgender individuals, alignment of physical characteristics with gender identity typically reduces gender dysphoria and improves mental health outcomes, as evidenced in clinical follow-up studies.

Starting at 18 means treatment occurs during a formative period for education, career development, and social relationships. Addressing hormonal deficiency or gender dysphoria at this stage can positively influence overall quality of life and psychological adjustment. However, realistic expectations are essential — changes occur gradually over months to years, and individual responses vary. Some effects are irreversible (voice deepening, facial hair, clitoral enlargement in transgender men), which is important for informed consent.

What to Expect from Testosterone Therapy

Testosterone therapy is available in several formulations, each with distinct pharmacokinetic profiles. Common preparations licensed and used in the UK include:

• Intramuscular injections — testosterone undecanoate (Nebido) administered every 10–14 weeks after an initial loading phase, or mixed testosterone esters (Sustanon 250) given every 2–3 weeks, providing sustained testosterone levels

• Transdermal gels (Testogel, Tostran, Testavan) — applied daily to the skin, offering steady hormone delivery with more stable blood levels but requiring consistent application and precautions to avoid transfer to others

• Subcutaneous injections — increasingly used in some specialist services, particularly gender clinics, allowing for self-administration and flexible dosing; however, this route is largely off-label in the UK and should be undertaken only with specialist agreement and monitoring

The timeline of changes varies considerably between individuals and depends on dosage, formulation, and baseline hormone levels. Generally:

Early changes (1–3 months): Increased energy, improved mood and libido, skin oiliness and possible acne, cessation of menstruation (in transgender men — though amenorrhoea does not guarantee contraception)

Intermediate changes (3–6 months): Voice deepening begins (irreversible), facial and body hair growth commences, muscle mass increases, body fat redistribution starts

Longer-term changes (6–24 months and beyond): Voice reaches final depth, facial hair becomes more established (though full beard development may take several years), muscle development continues, body shape masculinisation progresses

Ongoing monitoring is essential throughout treatment. According to UK guidance and product summaries of product characteristics (SmPCs), follow-up typically occurs at 3, 6, and 12 months, then annually if stable. Monitoring includes:

• Testosterone levels (trough levels for injectables; any time for gels) to ensure therapeutic range

• Full blood count — testosterone stimulates red blood cell production; haematocrit should be maintained below 0.54. If haematocrit exceeds 0.54, dose reduction or temporary cessation is required, and investigation for contributing factors (obstructive sleep apnoea, smoking, dehydration) should be undertaken

• Liver function tests, lipid profile, blood pressure, and weight

• Symptom review and assessment of treatment goals

Potential adverse effects include:

• Acne and oily skin

• Polycythaemia (raised haematocrit) and increased risk of venous thromboembolism

• Mood changes, including irritability or low mood

• Sleep apnoea (worsening or new onset)

• Androgenic alopecia (male-pattern hair loss)

• Transient gynaecomastia (breast tenderness) early in treatment due to aromatisation to oestradiol

• Reduced fertility due to suppression of spermatogenesis

For transdermal gels, specific precautions are necessary to prevent transfer to others: apply to clean, dry skin on shoulders, upper arms, or abdomen (as per product instructions); allow to dry fully before dressing; wash hands thoroughly after application; cover the application site with clothing; avoid skin-to-skin contact with others (especially children and pregnant women) until the site has been washed.

Patients should be counselled to report concerning symptoms promptly, including chest pain, severe headaches, leg swelling or pain, breathing difficulties, visual disturbances, or significant mood disturbances. Suspected adverse reactions should be reported via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Getting Assessed for Testosterone Treatment in the UK

Accessing testosterone therapy in the UK requires proper medical assessment through NHS or private healthcare services. The pathway differs depending on whether treatment is sought for hypogonadism or gender-affirming care.

For suspected hypogonadism:

Begin by consulting your GP, who will take a detailed medical history, perform a physical examination, and arrange initial blood tests. These typically include two early-morning (before 11:00 AM) total testosterone measurements, SHBG, LH, FSH, prolactin, full blood count, liver and thyroid function, and lipid profile. If hypogonadism is confirmed and an underlying cause requires investigation, referral to an endocrinologist is typically required. The endocrinologist will conduct comprehensive assessment, arrange further investigations if needed (such as pituitary imaging), and discuss treatment options. NHS waiting times for endocrinology appointments vary by region but may extend several months.

Red flags requiring urgent specialist referral include: testicular mass (urgent urology review); visual field defects, severe headache, or markedly raised prolactin suggesting pituitary pathology (urgent endocrinology or neurosurgical assessment).

For gender-affirming testosterone therapy:

Transgender individuals should request referral to a specialist NHS Gender Identity Clinic (GIC) through their GP. NHS gender services follow protocols requiring assessment by specialist clinicians before hormone prescription. However, NHS GIC waiting times are currently very lengthy — commonly several years and variable by clinic and region. Some individuals choose private gender services for faster access, though costs can be substantial. Private prescriptions may subsequently be transferred to NHS GPs for ongoing prescribing under shared-care arrangements, though not all GP practices or integrated care boards (ICBs) participate in such arrangements, and local policies vary.

Important considerations:

• Never purchase testosterone from unregulated online sources without prescription — unregulated products may be counterfeit, contaminated, incorrectly dosed, or contain harmful substances, posing serious health and legal risks

• Discuss fertility preservation before starting treatment, as testosterone suppresses sperm production; sperm banking should be offered and considered if future biological parenthood is desired

• Ensure you understand the commitment required — testosterone therapy for hypogonadism is typically lifelong; for gender affirmation it is usually long-term

• Ask about patient support resources — organisations such as the Testosterone Deficiency Association, LGBT Foundation, and NHS gender services provide valuable information and peer support

If you experience concerning symptoms whilst awaiting assessment or during treatment, contact your GP promptly. Seek urgent medical attention (999 or A&E) for: chest pain, severe breathing difficulties, sudden severe headache, visual disturbances, signs of blood clots (painful, swollen, red leg), or severe mood disturbance including suicidal thoughts.

Key UK resources:

• MHRA Yellow Card Scheme for reporting side effects: yellowcard.mhra.gov.uk

• NHS information on male hypogonadism and gender dysphoria treatment

• Electronic Medicines Compendium (emc) for patient information leaflets and summaries of product characteristics

• British Society for Sexual Medicine (BSSM) guidance on testosterone deficiency

• General Medical Council (GMC) guidance on consent and capacity (0–18 years: guidance for doctors)

Frequently Asked Questions