Testogel is a widely prescribed transdermal testosterone replacement therapy used to treat confirmed hypogonadism in men. Many patients and clinicians ask how much Testogel raises testosterone levels, measured in nanomoles per litre (nmol/L) in the UK. Whilst individual responses vary considerably, men with low baseline testosterone typically achieve levels within the mid-normal range (approximately 12–20 nmol/L) with appropriate dosing. The actual increase depends on baseline levels, dosage, absorption characteristics, and individual metabolic factors. This article explains how Testogel works, expected testosterone rises, factors affecting absorption, and essential monitoring requirements to ensure safe and effective treatment.

Understanding Testosterone Levels and Measurement in nmol/L

Testosterone is the primary male sex hormone, essential for maintaining muscle mass, bone density, libido, mood regulation, and overall wellbeing. In the UK, testosterone levels are measured in nanomoles per litre (nmol/L), which quantifies the concentration of testosterone circulating in the bloodstream.

Normal testosterone reference ranges vary between laboratories but typically fall between approximately 9–29 nmol/L for adult men, with levels naturally declining with age. The diagnosis of hypogonadism (testosterone deficiency) requires confirmation of low total testosterone on two separate early-morning blood tests (usually between 7am and 11am, when physiological levels peak), using the local laboratory reference range. Most UK laboratories use a threshold of approximately 8–12 nmol/L, though this varies. Diagnosis must be accompanied by clinical symptoms such as reduced libido, erectile dysfunction, fatigue, or mood disturbances. NICE guidance emphasises that testosterone levels should be measured in the early morning to ensure accurate assessment.

Initial diagnostic work-up should include measurement of luteinising hormone (LH), follicle-stimulating hormone (FSH), and prolactin to differentiate primary hypogonadism (testicular failure) from secondary hypogonadism (pituitary or hypothalamic dysfunction). In certain situations—such as obesity, altered sex hormone-binding globulin (SHBG) levels, or borderline total testosterone—calculation of free or bioavailable testosterone may be necessary. Factors such as obesity, chronic illness, medications (particularly opioids and corticosteroids), and age can significantly influence testosterone levels.

Red-flag features requiring specialist referral include very low testosterone with low or inappropriately normal gonadotrophins, raised prolactin, pituitary symptoms (headache, visual disturbance), testicular abnormalities, or markedly abnormal prostate-specific antigen (PSA) or digital rectal examination (DRE). Testosterone exists in different forms within the bloodstream: total testosterone (bound and unbound), free testosterone (biologically active), and bioavailable testosterone. Most routine testing measures total testosterone.

For men considering or currently using testosterone replacement therapy such as Testogel, understanding these measurements is crucial for monitoring treatment effectiveness and ensuring levels remain within the therapeutic range. Testosterone levels that are too low fail to alleviate symptoms, whilst excessively high levels may increase the risk of adverse effects including polycythaemia (increased red blood cell production) and mood disturbances.

How Testogel Works to Increase Testosterone

Testogel (testosterone gel) is a transdermal testosterone replacement therapy licensed in the UK for treating confirmed hypogonadism in men. The medication contains bioidentical testosterone in an alcohol-based gel formulation, available in two main strengths: Testogel 16.2 mg/g (commonly supplied in pump dispensers delivering 20.25 mg, 40.5 mg, or 81 mg of testosterone per application) and Testogel 1% (supplied in 50 mg sachets). Each product has specific application instructions that must be followed.

The mechanism of action involves direct absorption of testosterone through the skin into the systemic circulation. When applied to clean, dry, intact skin, the alcohol vehicle evaporates rapidly, leaving testosterone on the skin surface. The hormone then penetrates the stratum corneum (outer skin layer) and enters dermal capillaries, bypassing first-pass hepatic metabolism that occurs with oral testosterone preparations. This transdermal delivery provides steady testosterone levels.

Application sites differ by product strength. Testogel 16.2 mg/g should be applied to the shoulders and upper arms only; application to the abdomen is not recommended for this formulation. Testogel 1% may be applied to the shoulders, upper arms, or abdomen. The gel should be applied to clean, dry, intact skin as directed in the product-specific Summary of Product Characteristics (SmPC). Patients must not apply the gel to the genital area.

Once absorbed, testosterone circulates in the bloodstream, where approximately 98% binds to sex hormone-binding globulin (SHBG) and albumin, whilst the remaining 2% exists as free, biologically active testosterone. The hormone then exerts its effects by binding to androgen receptors in target tissues throughout the body, influencing gene transcription and protein synthesis.

Transfer precautions are essential. After application, patients must wash their hands thoroughly with soap and water. The application site should be allowed to dry for several minutes and should be covered with clothing to prevent transfer to others, particularly women and children. The timing before washing or swimming varies by product: Testogel 16.2 mg/g typically requires at least 2 hours, whilst Testogel 1% requires at least 6 hours. Patients should follow the specific instructions in their product leaflet.

Advantages of transdermal delivery include ease of dose adjustment and avoidance of injections. However, the formulation requires daily application and carries specific precautions regarding skin-to-skin contact with others until the application site has dried completely and been covered with clothing.

Expected Testosterone Rise with Testogel Treatment

The increase in testosterone levels achieved with Testogel varies considerably between individuals. Whilst some clinical data suggest average rises, individual responses depend heavily on baseline levels, dosage, absorption characteristics, and assay methods. Rather than focusing on a specific numerical increase in nmol/L, UK guidance emphasises achieving testosterone levels in the mid-normal range alongside symptom resolution.

Clinical experience demonstrates that men starting with low testosterone levels (below their laboratory's reference range) typically achieve therapeutic levels within days to weeks of initiating treatment. For instance, a man with a baseline testosterone of 8 nmol/L using a standard starting dose might expect levels to rise into the normal range (approximately 12–20 nmol/L), though individual variation is substantial. Some individuals may experience more modest increases, whilst others achieve greater rises.

Dose-response relationships exist within the therapeutic range. For Testogel 16.2 mg/g, the typical starting dose is 40.5 mg daily (two pump actuations), which may be adjusted based on clinical response and measured testosterone levels. Doses can be increased to 81 mg daily (four pump actuations) or reduced to 20.25 mg daily (one pump actuation) depending on individual requirements. For Testogel 1%, the starting dose is typically 50 mg daily (one sachet), with adjustments made in 25 mg increments. Dose adjustments should be guided by testosterone measurements and symptom response, following the specific product SmPC.

It is crucial to recognise that achieving levels within the mid-normal range and alleviating symptoms of hypogonadism are the primary treatment goals, rather than targeting a specific numerical increase. Some men achieve symptom resolution with testosterone levels at the lower end of the normal range, whilst others require levels towards the mid-to-upper range. Treatment should be individualised based on both biochemical parameters and clinical response, in accordance with guidance from the British Society for Sexual Medicine (BSSM) and the Society for Endocrinology.

Important safety considerations: Testosterone replacement therapy, including Testogel, suppresses spermatogenesis and should not be used in men actively seeking fertility. Alternative treatments should be considered in this population. Testogel is contraindicated in men with prostate cancer, breast cancer, or severe heart failure, and should be used with caution in those with cardiovascular risk factors.

Factors Affecting Testogel Absorption and Effectiveness

Multiple factors influence how effectively Testogel raises testosterone levels, contributing to the significant inter-individual variability observed in clinical practice. Understanding these variables helps optimise treatment outcomes and explains why some patients require dose adjustments.

Application technique and site selection significantly impact absorption. The gel must be applied to clean, dry, intact skin on the recommended areas specified in the product SmPC: shoulders and upper arms only for Testogel 16.2 mg/g; shoulders, upper arms, or abdomen for Testogel 1%. Skin thickness, blood flow, and surface area vary between sites, affecting absorption rates. Applying to damaged, inflamed, or excessively hairy skin reduces effectiveness. Patients should follow the specific wash-off and transfer precaution timings for their product to ensure adequate absorption and prevent transfer to others.

Body composition and metabolic factors play crucial roles. Obesity, particularly visceral adiposity, is associated with increased aromatase activity, which converts testosterone to oestradiol, potentially reducing circulating testosterone levels. Men with higher body mass index (BMI) may require higher Testogel doses to achieve therapeutic levels. Additionally, conditions affecting skin integrity or blood flow—such as peripheral vascular disease, diabetes, or dermatological conditions—can impair transdermal absorption.

Concurrent medications and medical conditions may influence testosterone therapy. Clinically relevant interactions listed in UK prescribing information include effects on anticoagulants (testosterone may enhance the effects of oral anticoagulants, requiring monitoring and possible dose adjustment), corticosteroids or adrenocorticotrophic hormone (ACTH) (increased risk of oedema, particularly in patients with cardiac, renal, or hepatic disease), and antidiabetic agents (possible changes in glycaemic control, requiring monitoring). SHBG levels, which are increased by hyperthyroidism, oestrogens, and ageing, affect the proportion of bioavailable testosterone. Conditions such as chronic kidney disease or liver dysfunction alter hormone metabolism and binding protein concentrations.

Lifestyle factors including alcohol consumption, smoking, sleep quality, and stress levels influence both endogenous testosterone production and the effectiveness of replacement therapy. Poor adherence—missing applications or inconsistent timing—reduces treatment effectiveness. Patients should be counselled on the importance of daily application at approximately the same time and proper technique to maximise therapeutic benefit. Consistent application and adherence to product-specific instructions are essential for optimal outcomes.

Monitoring Testosterone Levels During Testogel Therapy

Appropriate monitoring is essential to ensure Testogel therapy achieves therapeutic testosterone levels safely whilst minimising adverse effects. UK guidance from NICE, the British Society for Sexual Medicine (BSSM), and the Society for Endocrinology provides clear recommendations for monitoring schedules and parameters.

Initial monitoring should include baseline measurements before starting treatment: two early-morning (7am–11am) total testosterone levels to confirm hypogonadism, luteinising hormone (LH), follicle-stimulating hormone (FSH), and prolactin to establish the cause, full blood count (to assess haemoglobin and haematocrit), prostate-specific antigen (PSA) and consideration of digital rectal examination (DRE) in men at risk (typically those over 40 or with prostate risk factors, following UK guidance on age- and risk-adjusted thresholds), and liver function tests. Baseline assessment should also include cardiovascular risk factors, as testosterone therapy should be used with caution in men with pre-existing cardiovascular disease, and risk factors should be managed appropriately.

Follow-up testosterone measurements should be performed after steady-state levels are achieved, typically within 2–4 weeks of starting treatment or after dose adjustments. Blood samples should be taken at a consistent time relative to gel application, following the specific product SmPC recommendations (some products advise pre-dose sampling to reduce variability). The target is to achieve testosterone levels in the mid-normal range for the local laboratory reference range, guided by symptom resolution rather than arbitrary numerical targets. UK specialist guidance typically recommends aiming for the mid-normal range (approximately 12–20 nmol/L, depending on the laboratory).

Ongoing monitoring includes testosterone levels at 3 months, 6 months, and then annually if stable. However, full blood count should be monitored more frequently—at 3 months, 6 months, 12 months, and then annually—because testosterone therapy can stimulate erythropoiesis, potentially causing polycythaemia (haematocrit ≥0.54 or 54%). This complication increases thrombotic risk and may necessitate dose reduction, temporary treatment cessation, or investigation of contributing factors (such as sleep apnoea or smoking).

Additional monitoring parameters include PSA levels and consideration of DRE at intervals determined by baseline risk and UK guidance (typically annually in men over 40, with referral for abnormal DRE or age-adjusted PSA rise), liver function tests, and lipid profiles. Bone density assessment may be appropriate in men with osteoporosis or fracture risk. Patients should be advised to report symptoms suggesting excessive testosterone (aggression, mood changes, acne, oedema) or inadequate replacement (persistent fatigue, low libido). If testosterone levels remain below the therapeutic range despite dose optimisation and confirmed adherence, alternative formulations (intramuscular or subcutaneous testosterone) should be considered. Conversely, consistently elevated levels (above the upper limit of the reference range) require dose reduction to minimise adverse effects.

Important safety information: Testosterone replacement therapy suppresses spermatogenesis; men seeking fertility should not use Testogel. Contraindications include prostate cancer, breast cancer, and severe heart failure. Regarding cardiovascular risk, the European Medicines Agency (EMA) and MHRA have reviewed the evidence and concluded that there is no consistent evidence of increased cardiovascular risk with testosterone therapy; however, cardiovascular risk factors should be assessed and managed in all patients. Patients should be advised to report any suspected adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or by searching for MHRA Yellow Card in the Google Play or Apple App Store. Regular clinical review ensures treatment remains appropriate, effective, and safe throughout the duration of therapy.

Frequently Asked Questions