What are the side effects of Testogel? Testogel is a topical testosterone replacement therapy prescribed for men with confirmed testosterone deficiency (hypogonadism). Whilst most men tolerate treatment well, understanding potential side effects is essential for safe use. Common reactions include skin irritation at the application site, acne, and mood changes, whilst serious but rare complications may involve cardiovascular events or allergic reactions. This article examines the full spectrum of Testogel side effects, from mild skin reactions to serious adverse events requiring immediate medical attention, alongside guidance on safe application, monitoring requirements, and when to seek help.

What Is Testogel and How Does It Work?

Testogel is a topical testosterone replacement therapy (TRT) prescribed for men with confirmed testosterone deficiency, also known as hypogonadism. This condition occurs when the testes produce insufficient testosterone, leading to symptoms such as reduced libido, fatigue, decreased muscle mass, mood changes, and erectile dysfunction. Testogel is available in the UK in two formulations: Testogel 1% sachets (applied to shoulders, upper arms, or abdomen) and Testogel 16.2 mg/g pump (applied only to shoulders or upper arms).

The active ingredient, testosterone, is absorbed through the skin into the bloodstream, where it supplements the body's natural hormone levels. Once absorbed, testosterone binds to androgen receptors throughout the body, influencing numerous physiological processes. These include the maintenance of muscle mass and bone density, regulation of fat distribution, production of red blood cells, and support of sexual function and mood. The transdermal delivery system provides relatively stable testosterone levels, avoiding the large peaks and troughs seen with some injectable regimens.

Mechanism of action: After application, testosterone penetrates the skin and enters systemic circulation. The hormone is then metabolised primarily in the liver to various metabolites, including dihydrotestosterone (DHT) and oestradiol, which contribute to both therapeutic effects and potential adverse reactions.

Before starting Testogel, patients should undergo thorough evaluation including blood tests to confirm low testosterone levels on at least two separate morning occasions. Assessment should include LH/FSH levels, consideration of prolactin measurement, evaluation of the cause (primary vs secondary hypogonadism), and baseline checks of PSA, digital rectal examination and haematocrit. The MHRA and NICE emphasise that TRT should only be initiated when there is clear biochemical and clinical evidence of testosterone deficiency, as inappropriate use carries significant health risks.

Common Side Effects of Testogel

Most men using Testogel tolerate the treatment well, but like all medicines, it can cause side effects. Understanding these common reactions helps patients distinguish between expected, manageable effects and those requiring medical attention.

Skin reactions at the application site are among the most frequently reported side effects. These may include:

• Redness, itching, or irritation where the gel is applied

• Dry skin or mild rash

• Acne or oily skin, particularly on the face, chest, and back

• Contact dermatitis in sensitive individuals

These local reactions typically resolve with continued use or by rotating application sites. If persistent or bothersome, patients should consult their GP, who may recommend adjusting the application technique or prescribing a mild topical corticosteroid.

Hormonal and metabolic effects may include:

• Increased red blood cell production (polycythaemia/erythrocytosis)

• Mood changes, including irritability

• Breast tenderness or enlargement (gynaecomastia) due to conversion of testosterone to oestradiol

• Changes in libido

• Fluid retention

Other possible side effects include headache, dizziness, and potential changes in blood pressure and lipid levels. Some men experience hair loss or increased body hair growth, reflecting testosterone's effects on hair follicles.

Patients should be aware that prostate-specific antigen (PSA) levels may show small increases during treatment. This requires monitoring to distinguish normal increases from those suggesting prostate pathology. Regular blood tests, typically every 3–6 months initially and then annually, are essential to monitor testosterone levels, haematocrit, PSA, liver function, and lipid profiles.

It is important to note that many of these side effects may improve with dosage adjustment under medical supervision. If haematocrit exceeds 54%, dose reduction, temporary interruption or discontinuation should be considered, and the cause investigated.

Serious Side Effects and When to Seek Medical Help

Whilst most side effects of Testogel are mild and manageable, certain serious adverse reactions require immediate medical attention. Patients and their families should be vigilant for warning signs that indicate potentially dangerous complications.

Cardiovascular effects: Evidence regarding cardiovascular risk with testosterone therapy is inconclusive. The MHRA advises caution, particularly in men with pre-existing cardiovascular disease. Seek emergency medical help immediately if you experience:

• Chest pain, pressure, or tightness

• Sudden shortness of breath or difficulty breathing

• Pain radiating to the arm, jaw, or back

• Sudden severe headache, confusion, or difficulty speaking

• Weakness or numbness on one side of the body (potential stroke symptoms)

• Swelling, pain, or tenderness in the legs (possible deep vein thrombosis)

Severe allergic reactions, though rare, can occur. Stop using Testogel and call 999 or go to A&E if you develop:

• Difficulty breathing or swallowing

• Swelling of the face, lips, tongue, or throat

• Severe skin rash with blistering or peeling

• Rapid heartbeat with dizziness or fainting

Liver problems are rare with transdermal testosterone but may occur, particularly in those with pre-existing liver conditions. Contact your GP if you develop persistent nausea, unusual tiredness, yellowing of the skin or eyes (jaundice), dark urine, or pale stools.

Psychiatric effects occasionally include mood disturbances, depression, anxiety, or aggressive behaviour. If you or your family notice significant personality changes, suicidal thoughts, or uncharacteristic aggression, contact your GP promptly or call NHS 111 for advice.

Priapism (prolonged, painful erection lasting more than 4 hours) is a medical emergency requiring immediate treatment to prevent permanent damage. This is rare but requires urgent hospital attendance.

Prostate problems may develop or worsen during testosterone therapy. Seek medical advice if you experience new or worsening urinary symptoms such as difficulty passing urine, frequent urination, or urinary retention.

Patients should also contact their doctor if they develop signs of excessive red blood cell production, such as persistent headaches, dizziness, visual changes, ruddy complexion, or shortness of breath, as erythrocytosis can increase thrombotic risk.

If you experience any suspected side effects, you can report them via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Who Should Not Use Testogel?

Testogel is contraindicated in certain patient groups due to safety concerns. Healthcare professionals must carefully screen patients before prescribing, and individuals should disclose their complete medical history.

Absolute contraindications include:

• Known or suspected prostate cancer or breast cancer: Testosterone can stimulate growth of hormone-sensitive tumours

• Hypersensitivity: Known allergy to testosterone or any gel excipients

Testogel is not indicated for use in women or children. Accidental exposure through skin contact can cause virilisation in women (deepening voice, facial hair, clitoral enlargement) and premature sexual development in children. This risk necessitates strict precautions regarding application and contact with others. Pregnant or breastfeeding women should avoid all contact with Testogel application sites and wash immediately after any inadvertent contact.

Cautions and special warnings apply to men with:

• Severe cardiac, hepatic, or renal insufficiency (risk of fluid retention and oedema)

• Polycythaemia (haematocrit >54%)

• Thrombophilia or history of venous thromboembolism

• Uncontrolled hypertension

• Obstructive sleep apnoea (may worsen with TRT)

• Severe lower urinary tract symptoms or benign prostatic hyperplasia

• Diabetes (testosterone affects insulin sensitivity)

Men trying to conceive should be aware that testosterone therapy suppresses sperm production and can cause infertility. TRT is not appropriate for men wishing to maintain fertility, and alternative treatments should be discussed.

The MHRA emphasises that Testogel should only be prescribed for confirmed hypogonadism with both biochemical evidence (low testosterone on repeated testing) and clinical symptoms. It is not licensed for performance enhancement, anti-ageing, or treatment of non-specific symptoms in men with normal testosterone levels, as risks outweigh benefits in these contexts.

Managing Side Effects and Safe Use of Testogel

Successful testosterone replacement therapy requires not only appropriate prescribing but also patient education regarding safe application, monitoring, and side effect management. Following best practice guidelines minimises risks and optimises therapeutic outcomes.

Application technique is crucial for both efficacy and safety:

For Testogel 1% sachets:

• Apply to clean, dry, intact skin on shoulders, upper arms, or abdomen (not genital area)

• Avoid swimming or showering for at least 6 hours after application

For Testogel 16.2 mg/g pump:

• Apply only to shoulders or upper arms

• Avoid swimming or showering for at least 2 hours after application

For both formulations:

• Wash hands thoroughly with soap and water immediately after application

• Allow the gel to dry completely (3–5 minutes) before dressing

• Cover the application site with clothing once dry

• Rotate application sites to minimise local skin reactions

• The gel is flammable until dry—avoid smoking and open flames during and immediately after application

Preventing transfer to others is essential, as testosterone can be transmitted through skin-to-skin contact:

• Avoid close physical contact with women and children until the gel has dried and the area is covered

• If contact occurs, the exposed person should wash the area immediately with soap and water

• Wash the application site before situations involving close contact

• Use a barrier (clothing or towel) during unavoidable contact

• Wash bed linens and clothing that may have contacted the application site

Managing common side effects:

• For skin irritation: Rotate application sites, use fragrance-free moisturisers, and consider applying the gel at night to minimise daytime irritation

• For acne: Maintain good skin hygiene, use non-comedogenic products, and consult your GP if over-the-counter treatments are insufficient

• For mood changes: Keep a symptom diary, maintain regular sleep patterns, and discuss persistent issues with your healthcare provider

• For fluid retention: Reduce salt intake, elevate legs when resting, and report significant swelling to your doctor

Regular monitoring is mandatory for safe TRT:

• Blood tests at 3, 6, and 12 months, then annually, checking testosterone levels, haematocrit, PSA, liver function, and lipid profile

• Reduce or withhold dose if haematocrit exceeds 54%

• Investigate rapid PSA rises and follow NICE guidance for urology referral if indicated

• Blood pressure checks at each review

• Prostate examination as clinically indicated, particularly in men over 50

• Bone density assessment if indicated

• Review of symptoms and treatment response

Patients should attend all scheduled appointments and report new symptoms promptly. Never adjust the dose without medical advice, and do not share Testogel with others, as this is both illegal and dangerous. If you miss a dose, apply it as soon as you remember unless it is nearly time for the next dose—never double up.

For optimal results, combine TRT with lifestyle modifications: maintain a healthy weight, exercise regularly, ensure adequate sleep, limit alcohol, avoid smoking, and manage stress. These measures enhance treatment efficacy and reduce cardiovascular risk.

If side effects become intolerable or treatment goals are not met, discuss alternatives with your doctor, such as different TRT formulations (injections, patches, or implants) or adjunctive therapies. The goal is sustainable, safe hormone replacement that improves quality of life whilst minimising risks.

Report any suspected side effects via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

Frequently Asked Questions