Testogel is a transdermal testosterone replacement therapy prescribed for men with clinically confirmed hypogonadism—abnormally low testosterone levels. Applied daily to the skin, the gel delivers testosterone directly into the bloodstream, restoring hormone levels and alleviating symptoms such as fatigue, reduced libido, and decreased muscle mass. Whilst testosterone absorption begins within hours and blood levels stabilise within days, noticeable symptomatic improvements typically emerge over weeks to months, depending on the specific effect. Understanding the expected timeline, influencing factors, and monitoring requirements is essential for men considering or starting Testogel treatment in the UK.

What Is Testogel and How Does It Work?

Testogel is a transdermal testosterone replacement therapy (TRT) prescribed for men with clinically confirmed hypogonadism—a condition characterised by abnormally low testosterone levels. In the UK, Testogel is available in two formulations: a 50 mg/5 g (1%) gel in sachets and a 16.2 mg/g gel in a metered-dose pump. The gel is applied once daily to clean, dry, intact skin on the shoulders and upper arms (both formulations) or abdomen (1% sachets only). The gel is absorbed through the skin, delivering testosterone directly into the bloodstream.

The mechanism of action involves the passive diffusion of testosterone across the stratum corneum (the outermost skin layer) into dermal capillaries. Once absorbed, testosterone circulates systemically and binds to androgen receptors in target tissues throughout the body, including muscle, bone, brain, and reproductive organs. This binding initiates a cascade of physiological effects that restore normal testosterone-dependent functions.

Testosterone plays crucial roles in maintaining muscle mass and strength, bone density, libido, mood regulation, cognitive function, and energy levels. In men with hypogonadism, deficiency can lead to fatigue, reduced sexual function, depression, decreased muscle mass, and increased body fat. Testogel aims to restore testosterone to physiological levels, thereby alleviating these symptoms.

In the UK, Testogel is a prescription-only medicine regulated by the Medicines and Healthcare products Regulatory Agency (MHRA). Treatment should only be initiated following comprehensive clinical assessment, including at least two early-morning (ideally between 8 and 11 am) serum testosterone measurements. UK guidance from the Society for Endocrinology and the British Society for Sexual Medicine (BSSM) typically recommends treatment when testosterone is below 8 nmol/L with symptoms; levels between 8 and 12 nmol/L may warrant treatment if symptoms are present and free testosterone is low (calculated using sex hormone-binding globulin [SHBG] and albumin). Baseline investigations should include luteinising hormone (LH), follicle-stimulating hormone (FSH), prolactin, SHBG, full blood count (FBC) with haematocrit, prostate-specific antigen (PSA), and digital rectal examination (DRE) where appropriate. Pituitary evaluation may be needed if secondary hypogonadism is suspected.

Contraindications include known or suspected prostate cancer or male breast cancer. Caution is required in men with severe cardiac, hepatic, or renal disease. Men actively trying to conceive should not use Testogel, as exogenous testosterone suppresses spermatogenesis; specialist referral to andrology or endocrinology should be considered in such cases.

How Long Does Testogel Take to Work?

The timeframe for Testogel to produce noticeable effects varies considerably depending on which symptoms are being addressed. Testosterone absorption begins within hours of application, with serum testosterone levels typically reaching near steady-state concentrations within around 2 to 3 days of daily use, as documented in the product's Summary of Product Characteristics (SmPC). However, achieving stable blood levels does not equate to immediate symptomatic improvement.

Certain effects manifest relatively quickly. Many men report improvements in mood, energy levels, and sense of wellbeing within 2 to 4 weeks of starting treatment. Sexual function parameters, including libido and erectile quality, may begin to improve within 3 to 6 weeks, though maximal benefits often require 3 to 6 months of consistent therapy.

Physical changes generally take longer to become apparent. Increases in muscle mass and strength typically become noticeable after 3 to 6 months, with continued improvements over 12 months or more. Changes in body composition, including reduction in fat mass, follow a similar timeline. Improvements in bone mineral density—an important consideration for men with osteoporosis or osteopenia—require at least 6 to 12 months of treatment, with ongoing benefits accruing over several years.

It is important to recognise that individual responses vary significantly. Some men experience rapid symptomatic relief, whilst others require dose adjustments or longer treatment durations to achieve optimal results. Regular monitoring through blood tests (typically at 3 months, then 6 to 12 monthly) allows clinicians to assess treatment efficacy and make necessary adjustments. If there is no meaningful symptomatic improvement after 3 to 6 months despite achieving on-target testosterone levels, the diagnosis should be reconsidered, comorbidities addressed, or therapy discontinued. Patients should maintain realistic expectations and understand that testosterone replacement is typically a long-term commitment rather than a quick fix.

Factors That Affect How Quickly Testogel Works

Several variables influence how rapidly and effectively Testogel produces clinical benefits. Application technique is paramount—the gel must be applied to clean, dry, intact, healthy skin and allowed to dry completely (typically 3 to 5 minutes) before dressing. The gel should never be applied to the genitals (risk of excessive absorption and irritation) or to broken or inflamed skin. The minimum interval before showering or swimming differs by formulation and should follow the product SmPC; patients should check with their prescriber or pharmacist for specific guidance. Inconsistent application or premature washing can significantly reduce testosterone absorption and delay therapeutic effects.

Skin characteristics affect absorption rates. Thicker skin, excessive body hair, or dermatological conditions may impair penetration. Conversely, damaged or inflamed skin can increase absorption unpredictably, potentially leading to supraphysiological levels. The application site also matters—for the 1% sachets, approved sites are shoulders, upper arms, or abdomen; for the 16.2 mg/g pump, only shoulders and upper arms are approved. Rotating between approved areas can optimise absorption whilst minimising local skin reactions.

Baseline testosterone levels and severity of hypogonadism influence response time. Men with profoundly low testosterone may require higher doses or longer treatment periods to achieve symptomatic improvement compared to those with borderline deficiency. Age is another consideration—older men may experience slower or less pronounced responses, particularly regarding muscle mass and sexual function, due to age-related changes in androgen receptor sensitivity and overall health status.

Concurrent medical conditions can impact treatment efficacy. Obesity, metabolic syndrome, type 2 diabetes, and chronic inflammatory conditions may blunt testosterone's effects and prolong the time to symptomatic improvement. Lifestyle factors—including diet, exercise, sleep quality, alcohol consumption, and smoking—significantly influence treatment outcomes. Men who adopt healthy lifestyle modifications alongside TRT typically experience faster and more substantial benefits.

Medication interactions warrant consideration. According to the SmPC, testosterone may enhance the effects of oral anticoagulants such as warfarin (requiring INR monitoring), and may reduce insulin or oral antidiabetic requirements in diabetic men (necessitating blood glucose monitoring). Concurrent use with adrenocorticotrophic hormone (ACTH) or corticosteroids increases the risk of fluid retention and oedema. Whilst opioids and certain anticonvulsants can suppress endogenous testosterone production, they are not primary interactions with exogenous testosterone gel. Adherence to the prescribed regimen is crucial—missing doses or inconsistent application patterns will delay therapeutic effects and prevent achievement of steady-state testosterone levels.

What to Expect During Testogel Treatment

When initiating Testogel therapy, patients should anticipate a structured monitoring programme to ensure safety and efficacy. Initial assessment includes comprehensive blood tests measuring testosterone, LH, FSH, prolactin, SHBG (to calculate free testosterone if borderline), FBC with haematocrit, PSA, and liver function. A digital rectal examination may be performed in men over 50 or those with prostate symptoms to exclude prostate pathology before starting treatment.

Dosing varies by formulation. For the 1% sachets, the usual starting dose is 50 mg daily (one sachet), with a dose range of 25 to 100 mg daily. For the 16.2 mg/g metered-dose pump, the usual starting dose is 40.5 mg daily (two pump actuations), with dose adjustments in increments of 20.25 mg (one actuation) according to the SmPC. Doses are titrated based on clinical response and testosterone levels measured at follow-up.

During the first three months, patients typically attend follow-up appointments to assess symptomatic response and check testosterone levels. Blood samples should be taken at a time specified by the product SmPC or local protocol—commonly 2 to 4 hours after gel application—to measure levels within the therapeutic range. Dose adjustments may be necessary based on individual response and blood results.

Common side effects include application site reactions (redness, itching, or dryness), acne, increased body hair growth, and changes in libido. Gynaecomastia (breast enlargement) and male-pattern hair loss may also occur. These are generally mild and often resolve with continued use. More significant adverse effects requiring medical attention include:

• Polycythaemia (elevated red blood cell count and haematocrit)—monitored through regular FBC. If haematocrit exceeds 0.54, treatment should be withheld or reduced, and underlying causes investigated.

• Prostate enlargement or rising PSA levels—a PSA rise greater than 1.4 ng/mL in 12 months, PSA above 4 ng/mL, or an abnormal DRE should prompt consideration of urology referral.

• Fluid retention causing ankle swelling, particularly with concurrent corticosteroid use.

• Mood changes, including irritability or aggression.

• Sleep apnoea worsening (particularly in obese men).

• Blood pressure changes.

Transfer risk is an important safety consideration. Testosterone can transfer to others through close skin contact, potentially causing virilisation in women and children and posing risks during pregnancy. Patients must wash hands thoroughly after application, cover treated areas with clothing once the gel has dried, and shower before intimate contact. Formulation-specific advice on washing and covering should be followed as per the SmPC. If transfer is suspected (e.g., partner developing acne, increased body hair, or signs of virilisation), medical advice should be sought immediately.

Fertility counselling is essential. Exogenous testosterone suppresses spermatogenesis and should be avoided in men actively trying to conceive. Specialist referral to andrology or endocrinology is recommended for men wishing to preserve or restore fertility.

Long-term management involves ongoing monitoring every 6 to 12 months, including testosterone levels, FBC with haematocrit, PSA, and clinical assessment. Treatment should be discontinued if there is lack of benefit after an adequate trial with on-target testosterone levels, if significant adverse effects occur (such as uncontrolled polycythaemia), or if prostate cancer is diagnosed. Patients experiencing chest pain, severe headaches, visual disturbances, or leg swelling should contact their GP urgently, as these may indicate serious complications requiring immediate assessment.

Patients are encouraged to report any suspected adverse reactions via the MHRA Yellow Card scheme (available at yellowcard.mhra.gov.uk or via the Yellow Card app), contributing to ongoing safety monitoring of this medicine.

Frequently Asked Questions