Tostran and Testogel are both licensed transdermal testosterone replacement therapies used to treat male hypogonadism in the UK. Whilst both deliver bioidentical testosterone through the skin, they differ in concentration, application volume, drying time, and dosing flexibility. There is no robust head-to-head evidence establishing that Tostran or Testogel is definitively the best option overall. The optimal choice depends on individual patient factors, tolerability, lifestyle considerations, and local formulary guidance. This article examines the key differences, effectiveness, safety profiles, and practical considerations to help patients and clinicians make informed decisions about testosterone replacement therapy.

What Are Tostran and Testogel?

Tostran and Testogel are both transdermal testosterone replacement therapies (TRT) licensed in the UK for treating male hypogonadism—a condition characterised by abnormally low testosterone levels confirmed by clinical symptoms and biochemical testing. Both products deliver bioidentical testosterone through the skin, providing a non-invasive alternative to intramuscular injections.

Testogel is manufactured by Besins Healthcare and is available in two UK formulations:

• Testogel 16.2 mg/g gel (pump dispenser): Each pump actuation delivers 1.25 g of gel containing 20.25 mg of testosterone. This formulation is licensed for application to clean, dry skin on the shoulders and upper arms only.

• Testogel 50 mg/5 g gel (sachets): Each 5 g sachet contains 50 mg of testosterone (1% strength). Sachets may be applied to the shoulders, upper arms, or abdomen.

Both Testogel formulations are applied once daily, and testosterone is absorbed over several hours following application.

Tostran (testosterone 2% gel) is produced by Kyowa Kirin and offers a more concentrated formulation. It is dispensed via a canister with a metered-dose pump, where each actuation delivers 0.5 g of gel containing 10 mg of testosterone. Tostran is applied once daily to clean, dry skin, typically on the shoulders or upper arms. The higher concentration means a smaller volume of gel is required to deliver equivalent testosterone doses. Application sites should be rotated, and the gel must not be applied to the genital area or broken skin.

Both medications work through the same mechanism: testosterone is absorbed through the skin into the bloodstream, where it exerts physiological effects on muscle mass, bone density, libido, mood, and energy levels. The MHRA licenses both products specifically for testosterone deficiency confirmed by clinical symptoms and biochemical testing. Neither product should be used for performance enhancement, age-related testosterone decline without confirmed hypogonadism, or when trying to conceive, as exogenous testosterone suppresses spermatogenesis.

For full prescribing information, refer to the electronic Medicines Compendium (eMC) Summary of Product Characteristics (SmPC) for each formulation and the British National Formulary (BNF) testosterone monograph.

Key Differences Between Tostran and Testogel

Whilst both gels deliver testosterone transdermally, several practical differences may influence prescribing decisions and patient preference. The table below summarises key product-specific characteristics according to UK SmPCs:

| Feature | Testogel 16.2 mg/g (pump) | Testogel 50 mg/5 g (sachets) | Tostran 2% gel (pump) | |---------|---------------------------|------------------------------|------------------------| | Testosterone per actuation/sachet | 20.25 mg per pump | 50 mg per sachet | 10 mg per pump | | Licensed application sites | Shoulders, upper arms | Shoulders, upper arms, abdomen | Shoulders, upper arms (rotate sites) | | Minimum time before washing/showering | ≥6 hours after application | ≥6 hours after application | ≥2–3 hours after application | | Sampling time for monitoring | 2–4 hours post-application | 2–4 hours post-application | As per SmPC and specialist advice |

Concentration and volume: Tostran's 2% concentration means patients apply a smaller volume of gel compared to Testogel formulations for equivalent testosterone doses. For instance, 50 mg of testosterone requires one Testogel 50 mg sachet, approximately 2.5 pump actuations of Testogel 16.2 mg/g, or 5 pump actuations of Tostran. This reduced volume with Tostran may improve tolerability for some patients, particularly those who find larger gel applications uncomfortable or time-consuming to dry.

Dosing flexibility: The different dose increments (20.25 mg for Testogel pump, 10 mg for Tostran pump, 50 mg for Testogel sachets) provide varying flexibility when adjusting doses based on serum testosterone monitoring. Dose adjustments should be guided by testosterone levels measured at the time specified in the relevant SmPC (typically 2–4 hours after application for Testogel formulations), aiming for mid-normal physiological range values (often approximately 15–30 nmol/L, though targets should be individualised).

Application sites: Testogel 16.2 mg/g pump is licensed for shoulders and upper arms only, whereas Testogel sachets may also be applied to the abdomen. Tostran is licensed for shoulders and upper arms, with advice to rotate application sites. All products emphasise avoiding application to the genital area due to high absorption rates and potential for transfer to partners, and avoiding broken or irritated skin.

Drying time and washing intervals: Product-specific advice differs. Testogel formulations recommend waiting at least 6 hours before washing or showering, whilst Tostran advises a minimum of 2–3 hours. Patients should cover application sites with clothing once dry and wash the application area before close skin-to-skin contact. Both gels are flammable until dry; avoid smoking or going near naked flames until the gel has dried completely.

Cost considerations: In England, the NHS prescription charge is a standard fee per item for patients who pay. Acquisition costs to the NHS and local formulary preferences may vary between products and by Integrated Care Board (ICB). Clinicians should consult their local formulary for guidance on preferred options.

Effectiveness: Tostran vs Testogel for Testosterone Replacement

Clinical efficacy for both Tostran and Testogel has been demonstrated in clinical trials, with both products effectively raising serum testosterone levels into the physiological range when used appropriately. However, there is no robust head-to-head comparative evidence establishing superiority of one product over the other in terms of clinical outcomes.

Both gels achieve steady-state testosterone levels within days of initiating treatment. Pharmacokinetic studies show that transdermal testosterone produces more physiological testosterone profiles compared to intramuscular depot injections, avoiding the supraphysiological peaks and subtherapeutic troughs associated with long-acting preparations. Serum testosterone levels typically reach maximum concentration within a few hours post-application (product-specific; consult the relevant SmPC), then gradually decline over 24 hours, necessitating once-daily dosing.

Absorption rates vary between individuals due to factors including skin thickness, application site, ambient temperature, and individual metabolism. Approximately 9–14% of applied testosterone is absorbed systemically, though this figure may differ by formulation. Both products demonstrate clinically meaningful bioavailability, though individual patient response may vary. This variability underscores the importance of biochemical monitoring. UK specialist guidance (e.g., British Society for Sexual Medicine, Society for Endocrinology) typically recommends checking testosterone levels at 3, 6, and 12 months after initiation or dose adjustment, then annually once stable, with sampling timed according to the product SmPC (commonly 2–4 hours post-application for Testogel formulations).

Symptom improvement with either gel typically includes increased energy, improved libido, enhanced mood, and gradual increases in muscle mass and bone density over months. Response timelines are comparable between products. Sexual function improvements may be noticed within 3–6 weeks, whilst changes in body composition require 3–6 months, and bone density improvements take 6–12 months or longer.

Fertility considerations: Exogenous testosterone suppresses the hypothalamic-pituitary-gonadal axis and spermatogenesis. Men wishing to conceive should not use testosterone replacement therapy. Alternative treatments or referral to a specialist fertility or endocrinology service should be considered.

Treatment adherence is crucial for effectiveness. The once-daily application schedule for both products supports compliance better than more frequent dosing regimens. Patient preference between the two gels—influenced by factors such as application volume, drying time, and tolerability—may affect long-term adherence, making individual suitability an important consideration when determining which product is most appropriate for a particular patient.

For detailed pharmacokinetic and pharmacodynamic data, consult the eMC SmPCs for Testogel and Tostran, and refer to UK specialist guidance from the British Society for Sexual Medicine or Society for Endocrinology.

Side Effects and Safety Considerations

Both Tostran and Testogel share similar safety profiles, as expected with bioidentical testosterone formulations. Understanding potential adverse effects and monitoring requirements is essential for safe and effective treatment.

Common adverse effects include:

• Application site reactions: Skin irritation, erythema, pruritus, or dryness occurs in approximately 5–10% of users. Rotating application sites and ensuring the skin is clean and dry before application may reduce this risk.

• Acne and oily skin: Increased sebum production affects some patients, particularly during initial treatment phases.

• Gynaecomastia: Breast tenderness or enlargement may occur due to peripheral conversion of testosterone to oestradiol.

• Oedema and weight gain: Fluid retention may occur, particularly in patients with cardiac, hepatic, or renal impairment.

• Mood and behavioural changes: Some patients report irritability, mood swings, increased libido, or aggression.

• Testicular atrophy: Suppression of endogenous testosterone production may lead to reduced testicular size.

• Hair loss: Androgenic alopecia may be exacerbated in predisposed individuals.

Prostate and urological effects: Testosterone may stimulate benign prostatic hyperplasia and should be used with caution in men with lower urinary tract symptoms. Baseline and periodic prostate-specific antigen (PSA) and digital rectal examination are recommended, particularly in men over 50 years. Refer urgently (in line with NICE NG12) if PSA is age-specifically elevated or if there are concerning urological symptoms.

Haematological effects: Testosterone stimulates erythropoiesis, potentially raising haematocrit and haemoglobin. Full blood count monitoring is recommended at baseline, 3, 6, and 12 months, then annually. If haematocrit exceeds 54%, treatment should be withheld until levels normalise, and underlying causes (e.g., sleep apnoea, smoking) should be investigated.

Cardiovascular considerations: The MHRA advises caution in patients with pre-existing cardiovascular disease. Evidence on cardiovascular risk remains debated; clinicians should assess individual risk factors and monitor blood pressure regularly. Patients with severe cardiac failure should be closely monitored due to the risk of fluid retention and oedema.

Sleep apnoea: Testosterone therapy may worsen obstructive sleep apnoea. Assessment and monitoring are warranted in symptomatic patients or those at risk.

Drug interactions: Testosterone may enhance the effects of oral anticoagulants (e.g., warfarin), requiring closer INR monitoring. It may also affect glycaemic control in diabetic patients and interact with corticosteroids, increasing fluid retention risk. Consult the BNF and relevant SmPCs for full interaction profiles.

Transfer risk: Testosterone can transfer to partners or children through skin-to-skin contact before the gel dries completely. Both manufacturers recommend:

• Washing hands thoroughly with soap and water immediately after application

• Covering application sites with clothing once the gel has dried

• Washing the application site with soap and water before close skin-to-skin contact or intimate activity

• Avoiding contact with children until the gel has dried completely

Flammability: Both gels are flammable until dry. Patients must avoid smoking or going near naked flames during and immediately after application.

Contraindications (per SmPCs) include androgen-dependent carcinoma of the prostate or male breast cancer. Caution is required in patients with severe cardiac, hepatic, or renal impairment due to the risk of oedema. Polycythaemia is not an absolute contraindication but requires monitoring and dose adjustment or withholding if haematocrit exceeds 54%.

Neither product should be used by women (particularly if pregnant or breastfeeding) or children. Pregnancy in partners represents a particular concern, as testosterone exposure may affect foetal development.

When to seek urgent medical help: Patients should contact their GP promptly if they experience significant mood changes, prolonged or painful erections, or signs of fluid retention (e.g., swelling of ankles or legs). They should seek urgent medical attention (call 999 or attend A&E) if they experience severe chest pain, acute shortness of breath, sudden weakness or numbness, or signs of a stroke.

Reporting side effects: Patients and healthcare professionals are encouraged to report suspected adverse reactions via the MHRA Yellow Card scheme (https://yellowcard.mhra.gov.uk or via the Yellow Card app).

For comprehensive safety information, consult the eMC SmPCs for Testogel and Tostran, the BNF, and MHRA Drug Safety Updates on testosterone therapy.

Which Testosterone Gel Is Right for You?

Determining whether Tostran or Testogel is most suitable requires individualised assessment, as there is no robust head-to-head evidence establishing overall superiority of one product over the other. The optimal choice depends on patient-specific factors, clinical circumstances, tolerability, and local formulary guidance.

Clinical considerations that may guide selection include:

• Skin sensitivity and tolerability: Patients with sensitive skin or a history of dermatological reactions may prefer Tostran's smaller application volume, though individual responses vary. Application site reactions can occur with any formulation, and rotating sites may help.

• Lifestyle factors: Those who prefer minimal gel application, have concerns about transfer to partners or children, or wish to shower or exercise sooner after application may favour Tostran (minimum 2–3 hours before washing) over Testogel formulations (minimum 6 hours).

• Dosing requirements and flexibility: The different dose increments (20.25 mg per actuation for Testogel 16.2 mg/g pump, 10 mg per actuation for Tostran pump, 50 mg per sachet for Testogel 1% sachets) provide varying flexibility when titrating testosterone levels. Fine-tuning may be easier with smaller increments, though both products allow effective dose adjustment.

• Application site preference: Patients who prefer or require abdominal application may choose Testogel 50 mg sachets, as the Testogel pump and Tostran are licensed for shoulders and upper arms only.

• Previous experience: Patients switching from one product to another due to tolerability issues, inadequate biochemical response, or personal preference may find the alternative formulation more suitable. Equivalent dosing can be calculated based on testosterone content, with subsequent monitoring ensuring therapeutic levels are maintained.

Prescribing decisions should involve shared decision-making between patient and clinician. Endocrinologists or specialist services typically initiate testosterone replacement therapy following confirmation of hypogonadism (clinical symptoms plus low serum testosterone on at least two separate morning samples). Ongoing prescribing is often transferred to general practice once treatment is stable and effective. Local formulary preferences may influence initial product selection, though patient preference, tolerability, and clinical response should guide long-term choice.

Monitoring requirements are similar across products but must follow product-specific SmPC guidance for sampling times and intervals. UK specialist guidance (e.g., British Society for Sexual Medicine, Society for Endocrinology) typically recommends:

• Testosterone levels: Measure at 3, 6, and 12 months after initiation or dose adjustment, then annually once stable. Sampling should be timed according to the product SmPC (commonly 2–4 hours post-application for Testogel formulations). Target levels are typically mid-normal physiological range (often approximately 15–30 nmol/L), individualised to symptom response.

• Full blood count and haematocrit: Baseline, then at 3, 6, and 12 months, and annually thereafter. Withhold treatment if haematocrit exceeds 54% and investigate underlying causes.

• Prostate assessment: Baseline PSA and digital rectal examination in men over 50 or those with lower urinary tract symptoms, then periodically as clinically indicated. Refer urgently if concerning findings (NICE NG12).

• Lipid profile, liver function, and blood pressure: Baseline and periodic monitoring as clinically appropriate.

• Symptom and treatment goal assessment: Regular review of energy, libido, mood, and quality of life to ensure treatment remains effective and appropriate.

Switching between products is straightforward if one gel proves unsuitable. Equivalent dosing can be calculated based on testosterone content (e.g., 50 mg testosterone from one Testogel sachet is approximately equivalent to 5 actuations of Tostran or 2.5 actuations of Testogel 16.2 mg/g pump). Subsequent biochemical monitoring ensures therapeutic levels are maintained.

Fertility counselling: Men wishing to father children should not use testosterone replacement therapy, as it suppresses spermatogenesis. Alternative treatments or referral to a fertility or endocrinology specialist should be considered.

Ultimately, the most suitable testosterone gel is the one that effectively normalises testosterone levels, improves symptoms, minimises side effects, and fits comfortably into the patient's daily routine and lifestyle. Both Tostran and Testogel can achieve these goals when prescribed appropriately, monitored carefully, and used in accordance with UK clinical guidance. Patients should discuss their individual circumstances, preferences, and any concerns with their healthcare provider to determine the most appropriate option for their testosterone replacement therapy.

For further information, consult the eMC SmPCs for Testogel and Tostran, the BNF testosterone monograph, and UK specialist guidance from the British Society for Sexual Medicine or Society for Endocrinology.

Frequently Asked Questions