Testogel is a widely prescribed testosterone replacement therapy (TRT) gel in the UK, used to treat hypogonadism in adult men. A common question among patients considering TRT is whether Testogel is bioidentical—that is, chemically identical to the testosterone naturally produced by the body. Understanding the distinction between bioidentical and synthetic hormones is important for informed treatment decisions. This article explains what Testogel is, confirms its bioidentical status, reviews its safety and effectiveness under UK guidance, and outlines alternative testosterone replacement options available through the NHS.

What Is Testogel and How Does It Work?

Testogel is a transdermal testosterone gel licensed in the UK for testosterone replacement therapy (TRT) in adult men with hypogonadism—a condition characterised by insufficient testosterone production. The active ingredient is testosterone, formulated as a clear, colourless hydroalcoholic gel applied daily to clean, dry skin.

Testogel is available in two main formulations in the UK:

• Testogel 50 mg/5 g (1%) sachets: applied to shoulders, upper arms, or abdomen

• Testogel 16.2 mg/g pump: each pump actuation delivers 20.25 mg testosterone; applied to shoulders or upper arms only

Once applied, the gel dries within minutes and is flammable until dry; patients should avoid open flames or smoking until the gel has dried and they are dressed. Testosterone is absorbed through the skin into the bloodstream, providing relatively steady serum levels over 24 hours. Pharmacokinetics vary by formulation: peak serum testosterone levels are typically reached within a few hours of application, with steady-state concentrations achieved after several days of consistent use.

Mechanism of action: Testosterone is an androgen hormone that binds to androgen receptors in various tissues, influencing protein synthesis, muscle mass, bone density, libido, mood, and secondary sexual characteristics. In men with hypogonadism, Testogel aims to restore physiological testosterone levels, alleviating symptoms such as fatigue, reduced libido, erectile dysfunction, loss of muscle mass, and mood disturbances.

Dosing is individualised based on serum testosterone monitoring and clinical response, with starting doses and titration schedules specified in the product's Summary of Product Characteristics (SmPC). Patients are advised to apply the gel at the same time each day, wash hands thoroughly immediately after application, and allow the application site to dry before dressing. The site should not be washed for at least 6 hours after application (1% formulation) or 2 hours (16.2 mg/g pump). Precautions must be taken to prevent transfer to others, particularly women (especially if pregnant), children, and partners, through skin-to-skin contact; covering the application site with clothing once dry and washing before intimate contact are essential.

Is Testogel Bioidentical Testosterone?

The term 'bioidentical' refers to hormones that are chemically and structurally identical to those produced naturally by the human body. Testogel contains bioidentical testosterone—the same molecular structure (C₁₉H₂₈O₂) as endogenous testosterone synthesised in the testes. The body recognises and metabolises it in exactly the same way as naturally produced testosterone, binding to the same receptors and undergoing identical metabolic pathways.

It is important to distinguish bioidentical testosterone from 17-alpha-alkylated synthetic androgens (such as methyltestosterone), which are structurally modified to enhance oral bioavailability but carry increased risks of hepatotoxicity and altered side-effect profiles. Testogel, as a licensed bioidentical product, avoids these specific risks.

Many other UK-licensed testosterone replacement products also deliver bioidentical testosterone. For example, injectable testosterone esters (such as testosterone enantate in Sustanon or testosterone undecanoate in Nebido) are prodrugs: once injected, the ester is hydrolysed in the body to release bioidentical testosterone. The key differences between formulations lie in their pharmacokinetic profiles (how quickly testosterone is released and how long it lasts), route of administration, and convenience, rather than in the testosterone molecule itself.

The term 'bioidentical' is sometimes used in unregulated compounding pharmacy contexts, which may lack the quality assurance and safety monitoring of licensed products. Testogel is a licensed, regulated bioidentical testosterone product approved by the Medicines and Healthcare products Regulatory Agency (MHRA), ensuring pharmaceutical-grade quality, consistency, batch-to-batch reliability, and adherence to UK safety standards. Patients should use MHRA-licensed testosterone products and avoid unlicensed compounded preparations, which are not subject to the same regulatory oversight.

Safety and Effectiveness of Testogel in the UK

Testogel is widely prescribed in the UK and has a well-established safety and efficacy profile when used appropriately under medical supervision. NICE Clinical Knowledge Summaries (CKS) and the British Society for Sexual Medicine (BSSM) recommend testosterone replacement therapy for men with confirmed hypogonadism: low serum testosterone on two separate early-morning samples, accompanied by clinical symptoms, with assessment of luteinising hormone (LH) and follicle-stimulating hormone (FSH) to evaluate underlying causes.

Effectiveness: Clinical trials demonstrate that Testogel effectively restores testosterone levels to the mid-normal physiological range in most men, with corresponding improvements in libido, sexual function, energy levels, mood, muscle mass, and bone density. Many patients report symptomatic improvement within 3–6 weeks, with maximal benefits often seen after 3–6 months of consistent therapy.

Contraindications include:

• Known or suspected prostate cancer or male breast cancer

• Severe cardiac, hepatic, or renal impairment predisposing to oedema

• Pregnancy and breastfeeding (Testogel is not indicated for use in women or children)

Common adverse effects include:

• Skin reactions at the application site (erythema, irritation, dryness)

• Acne or oily skin

• Mood changes (irritability; rarely, aggression)

• Gynaecomastia (breast tissue enlargement)

• Polycythaemia (increased red blood cell count)

• Benign prostatic hyperplasia symptoms

Important cautions:

• Fertility: TRT may suppress spermatogenesis and reduce fertility. Men wishing to father children should discuss this with their doctor before starting treatment and may require referral to endocrinology or andrology.

• Sleep apnoea: Testosterone may worsen obstructive sleep apnoea; patients with risk factors should be monitored.

• Oedema and cardiovascular risk: Caution is needed in men with cardiac, renal, or hepatic disease; fluid retention and hypertension may occur.

• Transference risk: Testosterone transferred to pregnant women via skin contact may harm the unborn baby. Patients must cover the application site with clothing once dry and wash the area before close physical contact.

Monitoring requirements (per NICE CKS and BSSM guidance) include baseline and follow-up assessments at approximately 3, 6, and 12 months, then annually:

• Serum testosterone levels (target: mid-normal range for age)

• Full blood count and haematocrit: if haematocrit exceeds 54%, treatment should be stopped or the dose reduced, and the patient evaluated for causes of polycythaemia

• Prostate-specific antigen (PSA) and digital rectal examination (DRE) in men over 40 or those at higher risk: refer to urology if PSA rises above age-specific reference ranges, increases rapidly, or if DRE is abnormal

• Liver function tests and lipid profile may be considered based on individual clinical indication and cardiovascular risk factors

There is no clear evidence that monitored testosterone replacement therapy increases the incidence of prostate cancer, but TRT is contraindicated in men with known or suspected prostate cancer, and careful monitoring is essential.

Patient safety advice: Wash hands thoroughly with soap and water immediately after applying Testogel. Cover the application site with clothing once the gel has dried. Avoid washing the site for the time specified in the product instructions (at least 6 hours for 1% gel, 2 hours for 16.2 mg/g pump). Avoid skin-to-skin contact with others, especially women and children, until the site is covered or washed. If accidental transfer occurs, the affected person should wash the area immediately with soap and water. Contact your GP promptly if you experience chest pain, leg swelling, breathing difficulties, persistent erections, significant mood changes, or any other concerning symptoms. Report suspected side effects via the MHRA Yellow Card scheme (https://yellowcard.mhra.gov.uk).

Alternatives to Testogel for Testosterone Replacement

While Testogel is a popular first-line option for testosterone replacement, several alternatives exist, each with distinct advantages and limitations. The choice depends on patient preference, lifestyle, contraindications, clinical response, and adherence.

Other transdermal testosterone gels licensed in the UK include:

• Tostran 2% gel (applied to abdomen, shoulders, or upper arms)

• Testavan 2% gel (applied to shoulders or upper arms)

These offer similar convenience and steady testosterone delivery, with differences in application sites and dosing schedules.

Intramuscular testosterone injections include:

• Testosterone enantate (e.g., Sustanon): administered every 2–4 weeks. Injections provide reliable testosterone delivery and eliminate concerns about transdermal transfer, but serum testosterone levels may fluctuate between doses, with corresponding variations in mood and energy. Some men experience injection site discomfort.

• Testosterone undecanoate (Nebido): long-acting injection given every 10–14 weeks after an initial loading phase. This option suits men seeking infrequent administration, though it requires intramuscular injection and cannot be easily reversed if side effects occur.

Testosterone patches offer an alternative transdermal option, applied nightly to the skin. They provide steady hormone delivery but availability in the UK is currently limited, and they may cause more frequent skin irritation than gels.

Oral, buccal, and implant formulations have limited or no availability in the UK. Oral testosterone undecanoate products previously available (e.g., Restandol) are largely discontinued or not marketed in the UK. Subcutaneous testosterone pellets (implants) and buccal tablets are not routinely available.

NICE CKS and BSSM guidance recommend individualising treatment choice based on patient preference, tolerability, clinical response, pharmacokinetic profile, and monitoring feasibility. If Testogel proves ineffective or poorly tolerated, switching to an alternative formulation is appropriate. Non-responders should be re-evaluated for secondary causes of symptoms and accuracy of the hypogonadism diagnosis, with consideration of specialist endocrinology referral.

Patients considering testosterone replacement should discuss all available options with their GP or endocrinologist, weighing convenience, lifestyle factors, adherence, and personal preferences. In England, a standard NHS prescription charge per item applies (with national exemptions for certain groups); Scotland, Wales, and Northern Ireland do not charge for prescriptions. The choice of formulation does not affect the prescription charge structure.

Frequently Asked Questions