Testogel is a widely prescribed testosterone replacement therapy in the UK, used to treat male hypogonadism when testosterone deficiency has been confirmed through blood tests and clinical symptoms. Whilst Testogel is generally safe when used correctly under medical supervision, it carries important safety considerations including potential side effects, contraindications, and risks of accidental transfer to others. Understanding how to use Testogel safely, who should avoid it, and what monitoring is required can help men make informed decisions about their treatment. This article examines the safety profile of Testogel, common concerns, and guidance aligned with UK regulatory standards from the MHRA, NICE, and specialist societies.

What Is Testogel and How Does It Work?

Testogel is a transdermal testosterone replacement therapy (TRT) licensed in the UK for treating male hypogonadism—a condition where the testes produce insufficient testosterone. It is available in two formulations: Testogel 50 mg/5 g (1% gel) supplied in sachets, and Testogel 16.2 mg/g (1.62% gel) supplied in a metered-dose pump dispenser. The Medicines and Healthcare products Regulatory Agency (MHRA) has approved Testogel for use when testosterone deficiency has been confirmed by clinical symptoms and biochemical tests.

The gel works by delivering testosterone through the skin directly into the bloodstream, bypassing first-pass hepatic metabolism. After application to clean, dry skin, testosterone is absorbed gradually, providing relatively stable serum levels throughout the day. This transdermal delivery system offers advantages over intramuscular injections, which can produce peaks and troughs in testosterone levels. Steady-state serum concentrations are typically achieved within a few days of regular daily application.

Once absorbed, testosterone exerts its effects by binding to androgen receptors in various tissues. It plays crucial roles in maintaining muscle mass and strength, bone density, libido, mood regulation, and secondary sexual characteristics. The body converts some testosterone to dihydrotestosterone (DHT) via 5-alpha reductase enzymes, and to oestradiol via aromatase enzymes—both metabolites contributing to testosterone's overall physiological effects.

Testogel is not suitable for enhancing athletic performance or bodybuilding in men with normal testosterone levels, nor is it licensed for use in women or children. The National Institute for Health and Care Excellence (NICE) Clinical Knowledge Summary (CKS) recommends that testosterone replacement should only be initiated after two early-morning serum testosterone measurements confirm deficiency, alongside relevant clinical symptoms such as reduced libido, erectile dysfunction, fatigue, or loss of muscle mass.

Common Side Effects and Safety Concerns with Testogel

Like all medicines, Testogel can cause side effects, although not everyone experiences them. The most frequently reported adverse effects relate to the skin at the application site, including dryness, irritation, redness, pruritus, or acne. These local reactions are generally mild and often resolve with continued use or by rotating application sites. If persistent or severe skin reactions occur, patients should consult their GP.

Systemic side effects may include:

• Mood changes: Some men report irritability, aggression, or mood swings, particularly if testosterone levels rise too rapidly or exceed physiological ranges

• Prostate effects: Testosterone can stimulate prostate tissue, potentially causing urinary symptoms or, rarely, contributing to prostate enlargement (benign prostatic hyperplasia). Changes in prostate-specific antigen (PSA) levels may occur

• Haematological changes: Testosterone stimulates red blood cell production, which may lead to polycythaemia (elevated haematocrit). Regular monitoring through full blood counts is recommended

• Gynaecomastia: Breast tissue enlargement can occur due to aromatisation of testosterone to oestradiol

• Sleep disturbances: Including sleep apnoea, particularly in men with pre-existing risk factors such as obesity

• Other effects: Headache, alopecia, hypertension, weight gain, and oedema have been reported

A significant safety concern involves accidental transfer to others, particularly women and children, through close skin-to-skin contact. Testosterone exposure in women can cause virilisation symptoms (deepening voice, excessive hair growth), whilst children may experience premature sexual development. The MHRA emphasises that application sites must be covered with clothing once the gel has dried, and hands should be washed thoroughly with soap and water immediately after application. Men should wash the application site with soap and water before close skin contact or sexual activity, particularly with pregnant partners.

Important safety warnings include:

• Flammability: The gel contains alcohol and is flammable until dry. Avoid fire, flames, or smoking until the gel has dried completely

• Drug interactions: Testosterone may enhance the effect of oral anticoagulants such as warfarin; the International Normalised Ratio (INR) should be monitored closely. Testosterone may also reduce insulin or oral antidiabetic requirements; blood glucose should be monitored in men with diabetes

• Fertility: Testosterone replacement therapy can suppress spermatogenesis and reduce fertility. Men planning to father children should discuss this with their doctor before starting treatment

Cardiovascular and thromboembolic safety has been the subject of MHRA Drug Safety Updates. Whilst evidence remains inconsistent, testosterone should be used with caution in men with severe cardiac, hepatic, or renal disease. Men with a history of venous thromboembolism (VTE) require careful assessment, as testosterone-induced polycythaemia may theoretically increase thrombotic risk. Men with existing heart disease, uncontrolled hypertension, or previous stroke require careful assessment before starting treatment.

If you experience any side effects, talk to your doctor or pharmacist. This includes any possible side effects not listed here. You can also report suspected side effects directly via the MHRA Yellow Card Scheme at www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store.

Who Should Not Use Testogel?

Testogel is contraindicated in several clinical situations where testosterone therapy may cause harm or exacerbate existing conditions. Absolute contraindications include:

• Prostate cancer or breast cancer: Testosterone can stimulate growth of hormone-sensitive tumours. Men with current or previous prostate or breast cancer should not use Testogel

• Hypersensitivity: Known allergy to testosterone or any excipients in the gel formulation

Special warnings and cautions require careful risk-benefit assessment:

• Severe cardiac, hepatic, or renal insufficiency: Testosterone may worsen fluid retention and cardiac function in men with decompensated heart failure or severe organ impairment. These conditions are not absolute contraindications but require close monitoring and specialist input

• Elevated prostate-specific antigen (PSA): Men with PSA levels above age-adjusted reference ranges or abnormal digital rectal examination require urological assessment before starting testosterone therapy

• Severe sleep apnoea: Testosterone may worsen obstructive sleep apnoea, particularly in obese men

• Polycythaemia: Pre-existing elevated haematocrit should be investigated and managed before initiating treatment. Many UK sources advise caution if haematocrit is markedly elevated (e.g., ≥0.50) and recommend withholding or reducing treatment if haematocrit reaches ≥0.54

• Epilepsy or migraine: These conditions may be exacerbated by testosterone therapy, requiring closer monitoring

• Venous thromboembolism: Men with a history of VTE or thrombophilia require individualised assessment, as testosterone-induced polycythaemia may increase thrombotic risk. The MHRA has issued warnings regarding VTE risk with testosterone therapy

Men with benign prostatic hyperplasia experiencing moderate to severe lower urinary tract symptoms should undergo urological evaluation before starting Testogel.

Fertility considerations: Testosterone replacement therapy can suppress spermatogenesis and impair fertility. Men who are planning to father children should discuss alternative treatments or specialist referral before starting Testogel.

It is essential that testosterone deficiency is confirmed biochemically before treatment. Testogel should not be used in men with normal testosterone levels seeking performance enhancement or anti-ageing benefits, as this constitutes off-label use with potential for harm. Testogel is not licensed for use in women or adolescents. The British Society for Sexual Medicine (BSSM) guidelines emphasise that symptoms alone, without biochemical confirmation, are insufficient to justify testosterone replacement therapy.

Safe Use of Testogel: Dosage and Application Guidelines

Safe and effective use of Testogel requires adherence to proper application techniques and dosing schedules, which differ between the two formulations.

Dosing:

• Testogel 50 mg/5 g (1% sachets): The usual starting dose is 50 mg of testosterone (one 5 g sachet) applied once daily in the morning

• Testogel 16.2 mg/g (1.62% pump): The usual starting dose is 40.5 mg of testosterone (2.5 g of gel, delivered as two pump actuations) applied once daily in the morning

Dosage adjustments are made based on serum testosterone levels, typically measured after steady state is achieved (within a few days of regular use). Blood sampling timing differs by formulation and should follow the Summary of Product Characteristics (SmPC) guidance. Morning application mimics the natural circadian rhythm of testosterone production.

Application technique is crucial for both efficacy and safety:

• Apply to clean, dry, intact skin. For Testogel 1% sachets, apply to shoulders, upper arms, or abdomen. For Testogel 16.2 mg/g pump, apply to shoulders and upper arms only (not the abdomen)

• Spread the gel thinly over a wide area to maximise absorption

• Allow the gel to dry completely (approximately 3–5 minutes) before dressing. The gel is flammable until dry; avoid fire, flames, or smoking during this time

• Wash hands thoroughly with soap and water immediately after application

• Cover the application site with clothing once dry to prevent transfer to others

• Wash the application site with soap and water before close skin-to-skin contact or sexual activity, particularly with pregnant partners or children

• Avoid swimming or showering for at least 6 hours after applying Testogel 1% sachets, or at least 2 hours after applying Testogel 16.2 mg/g pump

Monitoring requirements are essential for safe long-term use. NICE CKS and BSSM guidance recommend:

• Testosterone levels: Checked at 3 months after initiation or dose change, then at least annually

• Full blood count: To detect polycythaemia, checked at 3 months, then at least annually. Treatment should be withheld or reduced if haematocrit reaches ≥0.54

• PSA and digital rectal examination: Baseline measurement, then at 3 months, 12 months, and annually thereafter in men over 40 or those at higher prostate cancer risk

• Liver function tests: Periodically, particularly in men with hepatic risk factors

• Cardiovascular and metabolic parameters: Blood pressure, lipid profile, and glucose monitoring as clinically indicated

Local shared-care protocols may specify additional monitoring requirements.

Patient safety advice includes avoiding skin-to-skin contact with others until the application site is covered and washed. If accidental contact occurs, the exposed person should wash the area immediately with soap and water. Men should inform their GP if they experience urinary symptoms, persistent erections, mood changes, breathing difficulties during sleep, or signs of fluid retention. Testogel should be stored safely away from children and disposed of appropriately. Regular follow-up with healthcare professionals ensures that treatment remains both safe and effective, with dosage adjustments made according to clinical response and biochemical monitoring.

Frequently Asked Questions