Testogel (testosterone gel) is a widely prescribed transdermal hormone replacement therapy for men with hypogonadism. Understanding how much Testogel is absorbed through the skin is essential for optimising treatment outcomes and ensuring safe, effective testosterone replacement. Clinical studies demonstrate that approximately 9–14% of the applied testosterone dose enters systemic circulation following topical application. However, absorption rates vary between individuals due to factors including skin characteristics, application technique, and environmental conditions. This article examines the evidence on Testogel absorption, factors affecting bioavailability, and practical guidance for maximising therapeutic efficacy whilst minimising risks.

How Much Testogel Is Absorbed Through the Skin

Testogel (testosterone gel) is a transdermal hormone replacement therapy designed to deliver testosterone through the skin into the bloodstream. Clinical studies indicate that approximately 9–14% of the applied testosterone dose is absorbed systemically following topical application. This absorption rate has been established through pharmacokinetic studies conducted during the medication's development and is reflected in the Summary of Product Characteristics (SmPC) approved by the MHRA.

The absorption process occurs through passive diffusion across the stratum corneum, the outermost layer of the skin. Once testosterone penetrates this barrier, it enters the dermal capillaries and subsequently reaches systemic circulation. Peak serum testosterone concentrations typically occur at different times depending on the specific formulation, with most products showing peaks between 2–8 hours after application. Steady-state levels are generally achieved after several days of consistent daily use.

It is important to understand that the percentage absorbed can vary between individuals due to multiple physiological and environmental factors. The remaining testosterone that is not absorbed systemically forms a reservoir in the skin (where it can potentially transfer to others through direct contact) while the hydroalcoholic vehicle evaporates. This is why allowing the gel to dry completely before dressing is essential — typically requiring 3–5 minutes of drying time.

For 1% formulations (such as Testogel 50 mg/5 g sachets), a standard dose contains approximately 5g of gel delivering 50mg of testosterone. If approximately 10% is absorbed, this translates to roughly 5mg of testosterone entering the bloodstream. Other formulations (such as 16.2 mg/g or 2% gels) have different concentrations and dosing. Healthcare professionals monitor treatment efficacy through regular blood tests, measuring serum testosterone levels at the time specified in the product's SmPC (which varies by formulation) to ensure therapeutic targets are achieved.

Factors That Affect Testogel Absorption Rates

Multiple variables influence how effectively testosterone gel is absorbed through the skin, leading to inter-individual variation in treatment response. Understanding these factors helps both patients and clinicians optimise therapy and troubleshoot suboptimal results.

Skin characteristics play a fundamental role in absorption efficiency. Thicker skin, such as that found on the upper arms and shoulders (recommended application sites), may absorb testosterone differently compared to thinner skin areas. Skin hydration status also matters — excessively dry skin can impair absorption. Application should always be to clean, dry, intact skin; avoid applying to irritated or broken skin as this can cause unpredictable or increased absorption. Conditions such as eczema, psoriasis, or dermatitis at the application site can significantly alter absorption rates and should be reported to your GP.

Application technique critically affects bioavailability. Applying too much gel to a small area can lead to saturation, reducing the percentage absorbed. Conversely, spreading the gel too thinly over an excessively large area may also compromise absorption. The gel should be applied in a thin, even layer to clean, dry skin. Washing the application site before the recommended time (which varies by product—typically ≥6 hours for Testogel 1% and ≥2 hours for products like Testavan and Tostran) can remove unabsorbed testosterone and reduce systemic exposure.

Body composition and age influence absorption as well. Adipose tissue distribution, muscle mass, and age-related changes in skin thickness and blood flow can all affect transdermal drug delivery. Additionally, concurrent use of moisturisers, sunscreens, or other topical products on or near the application site may create a barrier that impedes testosterone penetration. These products should be applied at different times or to different body areas, and only after the gel has fully dried.

Environmental factors such as ambient temperature and humidity can also play a role, as increased skin temperature generally enhances transdermal absorption through vasodilation and increased skin permeability. Exercise or heat exposure soon after application may increase absorption rates.

Maximising Testogel Absorption: Application Guidelines

Proper application technique is essential for ensuring consistent and optimal absorption of testosterone gel. Following evidence-based guidelines can significantly improve treatment outcomes and minimise the risk of inadequate hormone replacement or unintended transfer to others.

Timing and preparation form the foundation of effective application. Apply testosterone gel at approximately the same time each day, preferably in the morning, to mimic the body's natural circadian rhythm of testosterone production. Before application, ensure the skin is clean, completely dry, and intact — avoid applying to broken, irritated, or recently shaved skin. Wash and dry your hands thoroughly before opening the gel packet or pump.

Application site selection should follow the manufacturer's instructions for your specific formulation. Depending on the product, recommended sites typically include the shoulders, upper arms, or abdomen (note that some formulations such as Testogel 16.2 mg/g should not be applied to the abdomen). Rotate application sites within the recommended areas to prevent skin irritation and maintain consistent absorption. Never apply testosterone gel to the genitals, as this can cause severe local irritation and is not an approved application site.

The application process itself requires care and attention. Apply the gel as directed in your product's patient information leaflet—either directly to the application site or into the palm of your hand as specified. Apply the gel in a thin, even layer over the designated area, using a surface area roughly equivalent to two palm sizes. Gently rub the gel into the skin until it appears dry — this typically takes 3–5 minutes. Always wash your hands thoroughly with soap and water immediately after application, regardless of which body area you've applied the gel to.

Post-application precautions are crucial for safety. The gel is flammable until dry—avoid flames, fire, and smoking during application. Allow the gel to dry completely before dressing. Avoid swimming, bathing, or showering for the time specified in your product's instructions (typically 2–6 hours depending on the formulation). Cover the application site with clothing once dressed to minimise transfer risk to others. If close skin-to-skin contact is expected, wash the application site thoroughly with soap and water beforehand to prevent transfer to partners, children, or pregnant women.

Signs Your Body Is Absorbing Testogel Properly

Effective testosterone absorption manifests through both subjective improvements in symptoms and objective changes in blood testosterone levels. Recognising these signs helps patients and clinicians assess whether the prescribed dose is appropriate and being absorbed adequately.

Clinical improvements typically emerge gradually over weeks to months of consistent treatment. Patients often report increased energy levels and reduced fatigue within 3–4 weeks of starting therapy. Mood improvements, including reduced irritability and better overall sense of wellbeing, may become apparent within 4–6 weeks. Libido and sexual function often improve within 3–6 weeks, though maximum benefits may take 3–6 months. Physical changes such as increased muscle mass and strength, along with decreased fat mass, generally require 3–12 months of treatment. Body hair growth and skin oiliness may increase, reflecting androgenic effects.

Laboratory monitoring provides objective evidence of adequate absorption. Your GP or endocrinologist will typically measure serum testosterone levels at the time specified in your product's SmPC (which varies by formulation) after you've been using the gel consistently for at least one week. For accurate comparison, blood tests should be taken at the same time of day relative to gel application for all follow-up tests. Target testosterone levels generally fall within the normal physiological range for adult males (typically 10–30 nmol/L, though specific targets may vary based on individual circumstances and local laboratory reference ranges). British Society for Sexual Medicine (BSSM) guidelines emphasise the importance of correlating biochemical results with clinical response rather than treating numbers alone.

Additional markers that may be monitored include haematocrit and haemoglobin (as testosterone stimulates red blood cell production), prostate-specific antigen (PSA) in men over 40, and lipid profiles. If haematocrit rises above 0.54, your doctor may consider dose reduction or temporary treatment interruption. Improvements in bone mineral density may be assessed in patients with osteoporosis, though this requires longer-term treatment (12+ months).

If you experience appropriate symptom relief and your blood tests confirm testosterone levels within the therapeutic range, this indicates your body is absorbing testosterone gel effectively at your current dose. Signs of excessive absorption requiring medical review include persistent acne, irritability, oedema, or rising haematocrit.

What to Do If Testogel Absorption Seems Low

Suspected inadequate absorption of testosterone gel requires systematic evaluation and should always be discussed with your prescribing clinician. Never adjust your dose independently, as this can lead to supraphysiological testosterone levels or other complications.

Recognising potential absorption problems is the first step. Signs that may suggest inadequate absorption include persistent hypogonadal symptoms despite several weeks of treatment, such as ongoing fatigue, low libido, erectile dysfunction, or mood disturbances. However, these symptoms alone are insufficient for diagnosis — blood testing is essential to confirm subtherapeutic testosterone levels. Your GP will typically arrange blood tests to measure serum testosterone at the time specified in your product's SmPC, ensuring consistent timing for all follow-up tests.

If blood tests confirm low testosterone levels despite treatment, your healthcare provider will systematically investigate potential causes. First, they will review your application technique in detail — many cases of apparent poor absorption result from suboptimal application practices. Your doctor may ask you to demonstrate your application method or provide detailed instructions to ensure you're applying the gel correctly. They will also review the timing of your blood tests, as samples taken at inappropriate times may not reflect peak levels.

Potential interventions may include adjusting the dose (increasing the amount of gel applied), changing the application site, or switching to a different testosterone formulation. Some patients absorb gel preparations poorly and may benefit from alternative delivery methods such as intramuscular testosterone injections (e.g., testosterone undecanoate [Nebido] or testosterone enanthate). Your clinician will also investigate whether any medications you're taking or skin conditions might be interfering with absorption.

When to seek urgent advice: Contact your GP promptly if you develop signs of testosterone deficiency despite treatment, experience skin reactions at application sites, or have concerns about medication efficacy. Seek immediate medical attention if you experience symptoms of polycythaemia (headaches, dizziness, visual disturbances), chest pain, breathlessness, or if a partner or child shows signs of accidental testosterone exposure. Regular follow-up appointments (typically at 3 and 6 months initially, then annually) allow for ongoing monitoring and dose optimisation. Remember that achieving optimal testosterone replacement often requires individualised adjustment and patience, with most patients eventually finding an effective regimen through collaborative management with their healthcare team.

If you suspect a side effect from your medication, you can report it via the MHRA Yellow Card scheme.

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