Testogel is a transdermal testosterone replacement therapy licensed in the UK for treating male hypogonadism, a condition where the testes produce insufficient testosterone. Applied daily to the skin, Testogel delivers testosterone directly into the bloodstream, restoring hormone levels and alleviating symptoms such as low libido, fatigue, reduced muscle mass, and mood disturbances. Understanding how Testogel works, how to apply it correctly, and what to expect during treatment is essential for safe and effective use. This article explains the mechanism of action, application technique, expected timelines for results, and important safety considerations for men prescribed Testogel in the UK.

What Is Testogel and What Does It Contain?

Testogel is a transdermal testosterone replacement therapy (TRT) licensed in the UK for treating male hypogonadism—a condition where the testes produce insufficient testosterone. In the UK, Testogel is available as:

• Testogel 1% (50 mg testosterone per 5 g gel sachet or multi-dose pump)

• Testogel 16.2 mg/g (1.62% pump formulation)

(Note: A 2% testosterone gel is marketed as Tostran, not Testogel.)

The gel is supplied in single-dose sachets or multi-dose pump dispensers, with each application delivering a measured dose of testosterone. Common excipients include ethanol (which aids absorption and evaporates after application), carbomer (a gelling agent), isopropyl myristate, and purified water. The ethanol content means the gel is flammable until dry, and patients should avoid open flames or smoking immediately after application.

Mechanism of action: Once applied to the skin, testosterone is absorbed through the stratum corneum into the systemic circulation. The hormone then binds to androgen receptors in target tissues throughout the body, including muscle, bone, and the central nervous system. Once-daily transdermal delivery provides relatively stable testosterone levels over 24 hours, restoring physiological testosterone concentrations and alleviating symptoms of hypogonadism such as:

• Reduced libido and erectile dysfunction

• Fatigue and low energy

• Loss of muscle mass and strength

• Mood disturbances and poor concentration

• Decreased bone mineral density

Testogel is typically initiated by an endocrinologist or urologist, or under shared-care arrangements with primary care, following confirmed biochemical hypogonadism. Diagnosis requires two early-morning serum testosterone measurements (usually taken before 11 am) showing consistently low or borderline levels, alongside compatible clinical symptoms. UK guidance generally considers levels below 8 nmol/L as low and 8–12 nmol/L as borderline; interpretation should use local laboratory reference intervals for adult men.

Important considerations before starting:

Before prescribing Testogel, your clinician will perform a baseline assessment including:

• Repeat morning testosterone with luteinising hormone (LH), follicle-stimulating hormone (FSH), sex hormone-binding globulin (SHBG), and prolactin to distinguish primary (testicular) from secondary (pituitary/hypothalamic) hypogonadism

• Evaluation for pituitary disease if secondary hypogonadism is suspected—urgent referral is required if red-flag symptoms are present (visual field defects, persistent headaches, significantly elevated prolactin, or very low LH/FSH)

• Discussion of fertility: exogenous testosterone suppresses sperm production and is unsuitable for men trying to conceive; alternative treatments and sperm preservation should be discussed where appropriate

The Medicines and Healthcare products Regulatory Agency (MHRA) has approved Testogel for use with appropriate diagnosis confirmation and ongoing monitoring.

How to Apply Testogel Correctly for Best Results

Correct application technique is essential to ensure optimal testosterone absorption and minimise the risk of transfer to others. Testogel should be applied once daily, preferably at the same time each morning after showering or bathing, to clean, dry, intact skin.

Application sites (formulation-specific):

• Testogel 1% (50 mg/5 g): Apply to the shoulders, upper arms, or abdomen.

• Testogel 16.2 mg/g pump: Apply to the shoulders and upper arms only.

Do not apply to the genital area, as this increases the risk of local irritation and does not improve absorption. Rotate application sites within the permitted areas to prevent skin irritation.

Step-by-step application:

1. Wash and dry your hands thoroughly before opening the sachet or using the pump.
2. If using a new pump, prime it according to the instructions (usually 3 actuations discarded before first use).
3. Squeeze the entire contents of the sachet (or the prescribed number of pump actuations) onto one palm.
4. Apply the gel in a thin, even layer over the designated area. Gentle spreading is sufficient.
5. Allow the gel to dry fully before dressing. The alcohol evaporates, leaving testosterone on the skin surface.
6. Wash your hands thoroughly with soap and water immediately after application to prevent accidental transfer.

Important safety precautions:

• Avoid skin-to-skin contact with others (especially women and children) until after the specified interval: – Testogel 1%: Wait at least 6 hours, or wash the application site with soap and water before close contact. – Testogel 16.2 mg/g: Wait at least 2 hours, or wash the application site before close contact.

• Cover the application site with clothing once the gel is dry.

• If accidental contact occurs, the affected person should wash the area immediately with soap and water. Testosterone transfer can cause virilisation in females or premature puberty in children.

• Wait at least the formulation-specific interval before swimming or showering to ensure adequate absorption.

• Do not apply to broken, irritated, or inflamed skin.

• If you miss a dose, apply it as soon as you remember on the same day. Do not apply a double dose the next day.

• Dispose of used sachets carefully (fold and discard in household waste, out of reach of children and pets).

Patients should never share Testogel with others, even if they have similar symptoms. Testosterone is a controlled substance under the Misuse of Drugs Act 1971 (Class C), and unauthorised supply is illegal.

How Long Does Testogel Take to Work?

The timeframe for experiencing benefits from Testogel varies depending on which symptoms are being addressed, as different physiological processes respond at different rates to testosterone replacement.

Early effects (2–4 weeks): Some men notice improvements in mood, energy levels, and sense of wellbeing within the first few weeks of treatment. Libido may begin to increase during this period, though erectile function improvements typically take longer. These early changes reflect testosterone's effects on the central nervous system and neurotransmitter function.

Intermediate effects (3–6 months): Changes in body composition become more apparent during this phase. Muscle mass and strength gradually increase, whilst fat mass (particularly visceral adipose tissue) decreases. Erectile function and sexual performance generally improve within 3–6 months. Haemoglobin and haematocrit levels rise, which can improve oxygen-carrying capacity but requires monitoring to prevent polycythaemia.

Long-term effects (6–12 months and beyond): Bone mineral density improvements occur slowly, typically requiring 12–24 months of consistent therapy. Maximum benefits on body composition, muscle strength, and quality of life are usually achieved after 6–12 months of treatment.

Monitoring and dose adjustment: Blood tests are essential to ensure therapeutic testosterone levels are achieved. UK guidance (NICE Clinical Knowledge Summaries and British Society for Sexual Medicine) recommends checking serum testosterone levels at 3–6 months after starting treatment or after any dose change, then at least annually thereafter. The target is to achieve levels in the mid-normal range for adult men, interpreted using your local laboratory reference intervals. If levels remain low, the dose may be increased; if too high, it should be reduced.

Patients should also be monitored for:

• Haematocrit: Checked at baseline, at 3–6 months after starting or dose adjustment, then at least annually. If haematocrit rises above 0.54 (54%), treatment should be paused or the dose reduced, and the cause investigated. Venesection (therapeutic phlebotomy) may be considered if clinically indicated. Treatment may be resumed once haematocrit is within a safe range.

• Prostate monitoring: Baseline prostate-specific antigen (PSA) and digital rectal examination (DRE) in men aged 40–50 and over (depending on risk factors and local protocols), with periodic monitoring during treatment. Follow NICE guideline NG12 for suspected cancer referral thresholds (e.g., age-specific PSA elevation, abnormal DRE, or lower urinary tract symptoms with haematuria).

• Lipid profile and cardiovascular risk factors: Assessed at baseline and periodically.

• Bone density: If clinically indicated (e.g., history of fragility fractures or prolonged hypogonadism).

If symptoms do not improve after 6 months of confirmed mid-normal testosterone levels, alternative diagnoses should be considered, as not all symptoms attributed to low testosterone are testosterone-responsive.

Who Should Not Use Testogel?

Testogel is contraindicated in several clinical situations, and careful patient selection is essential to minimise harm. The MHRA and European Medicines Agency (EMA) provide clear guidance on absolute and relative contraindications.

Absolute contraindications:

• Prostate cancer or male breast cancer: Known or suspected prostate cancer or male breast cancer. Testosterone can stimulate growth of hormone-sensitive tumours. Prostate assessment (PSA and DRE where appropriate) is required before starting and during treatment. Carefully selected men with a history of successfully treated prostate cancer may occasionally be considered for TRT under close specialist supervision, but this is not routine practice.

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

• Women and children: Testogel is not licensed for use in women or children. (Some testosterone products are used off-label in specialist gender-affirming care services with tailored monitoring, but this is outside the licensed indication.) Accidental exposure can cause serious virilisation in females or premature puberty in children.

• Men trying to conceive: Exogenous testosterone suppresses spermatogenesis. Do not use TRT if you are trying to father a child; discuss alternative treatments and consider referral to andrology services. Sperm preservation may be appropriate in some cases.

Relative contraindications and cautions:

• Severe heart failure or fluid retention: Testosterone can cause sodium and fluid retention, exacerbating cardiac decompensation or oedema. The MHRA and EMA Pharmacovigilance Risk Assessment Committee (PRAC) reviewed cardiovascular risks and concluded that no consistent increased risk of cardiovascular events was identified, but testosterone should be used with caution in men with severe cardiac, hepatic, or renal disease due to the risk of oedema. Cardiovascular status should be monitored during treatment.

• Polycythaemia: Testosterone stimulates red blood cell production. Men with haematocrit above 0.54 (54%) should not start treatment until this is investigated and managed.

• Severe obstructive sleep apnoea: Testosterone may worsen sleep apnoea; assessment and treatment should precede TRT in symptomatic patients.

• Benign prostatic hyperplasia with severe lower urinary tract symptoms: Testosterone does not cause prostate cancer, but may worsen urinary symptoms in men with significant prostatic enlargement. Monitor lower urinary tract symptoms during treatment.

• Epilepsy or migraine: These conditions may be exacerbated by testosterone therapy and require closer monitoring.

• Severe hepatic or renal impairment: Risk of fluid retention and oedema; use with caution and monitor closely.

• History of venous thromboembolism (VTE) or thrombophilia: Use with caution; monitor for signs of thrombosis.

• Uncontrolled hypertension: Blood pressure should be optimised before starting TRT and monitored during treatment.

When to seek urgent medical advice:

Patients should contact their GP or specialist immediately if they experience:

• Chest pain, shortness of breath, or leg swelling (possible cardiovascular or thromboembolic events)

• Prolonged or painful erections lasting more than 4 hours (priapism—seek emergency care)

• Signs of liver dysfunction (jaundice, dark urine, persistent nausea, pale stools)

• Significant mood changes, aggression, anxiety, or depression

• Difficulty urinating, urinary retention, or blood in the urine (haematuria)

• Symptoms of polycythaemia (headache, dizziness, visual disturbances, flushing)

Regular follow-up with a healthcare professional experienced in testosterone therapy is essential to balance benefits against potential risks and ensure safe, effective treatment.

Reporting side effects: If you experience any side effects, talk to your doctor or pharmacist. You can also report suspected side effects directly via the MHRA Yellow Card scheme at https://yellowcard.mhra.gov.uk/ or search for MHRA Yellow Card in the Google Play or Apple App Store. Reporting helps provide more information on the safety of medicines.

Frequently Asked Questions