Testogel is a widely prescribed testosterone replacement therapy in the UK for men with confirmed hypogonadism. A common question is whether Testogel is body identical—and the answer is yes. Testogel contains bioidentical testosterone, meaning its molecular structure is identical to the hormone naturally produced by the human body. This distinguishes it from some synthetic hormone preparations that have been chemically modified. Understanding what "body identical" means, how Testogel works, and its safety profile is essential for men considering or currently using this treatment under medical supervision.

What Is Testogel and How Does It Work?

Testogel is a transdermal testosterone gel prescribed for testosterone replacement therapy (TRT) in men with confirmed hypogonadism—a condition characterised by abnormally low testosterone levels. The gel contains bioidentical testosterone, meaning the molecular structure of the hormone is identical to that naturally produced by the human body. This distinguishes it from synthetic analogues that have been chemically modified.

Testogel is available in two main formulations in the UK:

• Testogel 16.2 mg/g pump: Each full pump actuation delivers 20.25 mg of testosterone. This formulation is applied to the shoulders and upper arms only.

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

The gel is applied once daily to clean, dry, intact skin. Once applied, the testosterone is absorbed through the skin and enters the bloodstream gradually, providing more stable hormone levels throughout the day compared with short-acting intramuscular injections, which can cause peaks and troughs in testosterone levels. The dose is individualised based on clinical response and serum testosterone monitoring.

Mechanism of action: Testosterone binds to androgen receptors in various tissues, influencing protein synthesis, muscle mass, bone density, libido, mood, and secondary sexual characteristics. By restoring physiological testosterone levels, Testogel aims to alleviate symptoms of hypogonadism, including fatigue, reduced libido, erectile dysfunction, loss of muscle mass, and mood disturbances.

Application and safety instructions:

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

• Cover the application site with clothing once dry.

• Wash hands thoroughly with soap and water immediately after application.

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

• Wash the application site with soap and water before any situation involving close skin-to-skin contact with others (particularly women and children) to prevent unintended testosterone transfer.

• Do not apply to the genital area or broken skin.

• The gel is flammable until dry; avoid flames, smoking, or sparks near the application site until the gel has dried and the area is covered.

Accidental transfer of testosterone to others can cause serious adverse effects, including virilisation in women and precocious puberty in children. If a partner or child experiences unexpected signs such as genital changes, early development of pubic hair, increased erections, or aggressive behaviour, contact your GP immediately.

Differences Between Body Identical and Synthetic Hormones

The term "body identical" (also called bioidentical) refers to hormones that are chemically and structurally identical to those produced naturally by the human body. Testogel contains bioidentical testosterone, which means its molecular formula (C₁₉H₂₈O₂) matches endogenous testosterone exactly.

Synthetic hormones, by contrast, are chemically modified versions of natural hormones. These modifications are often made to alter pharmacokinetics—such as prolonging half-life or enabling oral administration—or to create patentable compounds. Examples include methyltestosterone (an oral synthetic androgen) and testosterone esters such as testosterone enanthate or cypionate used in injectable formulations. It is important to note that after administration, these esters are hydrolysed in the body to yield bioidentical testosterone; the differences lie in the delivery method and pharmacokinetic profile, not in the final active hormone or its receptor binding.

Key points include:

• Receptor binding and metabolism: Once in the body, bioidentical testosterone—whether from a gel or from an injectable ester after hydrolysis—binds to androgen receptors and is metabolised via the same pathways. Differences in safety and efficacy between formulations relate to route of administration, dose stability, and individual tolerability, not to differences in the testosterone molecule itself.

• Regulatory approval: All licensed testosterone preparations in the UK, whether labelled as bioidentical or formulated as esters, undergo rigorous evaluation by the MHRA and EMA. The term "body identical" describes molecular structure; it does not imply superiority in efficacy or safety.

• Distinction from unregulated products: In the UK, licensed testosterone products such as Testogel are regulated medicines with established quality, safety, and efficacy data. This differs from unregulated compounded "bioidentical" hormone preparations, which may lack standardised dosing, quality assurance, and regulatory oversight.

It is essential to understand that "bioidentical" does not mean "natural" or "risk-free". All hormone therapies, whether bioidentical or delivered via synthetic esters, carry potential risks and require medical supervision. The choice between formulations depends on clinical indication, patient preference, tolerability, and prescriber judgement informed by UK guidelines from bodies such as the British Society for Sexual Medicine (BSSM) and the Society for Endocrinology.

Safety and Effectiveness of Testogel for Testosterone Replacement

Testogel is an effective treatment for men with confirmed hypogonadism, with clinical trials demonstrating improvements in libido, sexual function, mood, energy levels, and body composition. However, like all medicines, it carries potential risks that must be weighed against benefits.

Common adverse effects include:

• Skin reactions: Application site irritation, rash, or acne

• Prostate effects: Benign prostatic hyperplasia (BPH) symptoms or elevated prostate-specific antigen (PSA)

• Haematological changes: Increased haemoglobin and haematocrit, which may raise the risk of thromboembolic events

• Mood and behaviour: Mood swings, aggression, or irritability in some individuals

• Gynaecomastia: Breast tissue enlargement due to peripheral conversion of testosterone to oestradiol

Serious but less common risks include:

• Cardiovascular events: Evidence regarding the risk of myocardial infarction and stroke remains uncertain. Baseline cardiovascular risk should be assessed and modifiable risk factors (including blood pressure, lipids, and diabetes) optimised before and during treatment.

• Venous thromboembolism (VTE): Testosterone therapy may increase the risk of deep vein thrombosis and pulmonary embolism, particularly in men with thrombophilia or other risk factors. Seek urgent medical attention if you experience leg pain, swelling, chest pain, or breathlessness.

Testosterone therapy is contraindicated in men with prostate or breast cancer. Caution is advised in those with severe heart failure, untreated obstructive sleep apnoea, or polycythaemia.

Monitoring requirements (as per UK guidance and product SmPC):

• Serum testosterone levels: Measured at baseline, 3–6 months after initiation or dose change, then at least annually. Sampling time varies by product; follow the specific SmPC instructions.

• Full blood count (haemoglobin and haematocrit): At baseline, 3–6 months, then at least annually. If haematocrit exceeds 54%, consider dose reduction or temporary cessation and investigate underlying causes.

• PSA and digital rectal examination: At baseline in men over 40 or those at increased risk of prostate cancer, then regularly (typically annually) during treatment.

• Blood pressure and lipid profile: Assess cardiovascular risk factors at baseline and monitor regularly.

• Liver function tests: Not routinely required for transdermal testosterone but may be requested based on clinical judgement.

When to seek medical advice:

Contact your GP or seek urgent medical attention if you experience:

• Chest pain, shortness of breath, or symptoms of stroke (sudden weakness, speech difficulty, facial drooping)

• Leg pain, swelling, warmth, or redness (possible VTE)

• Prolonged or painful erections (priapism)

• Significant mood changes, depression, or aggression

• Unexpected signs of testosterone transfer in a partner or child (genital changes, early pubic hair development, aggressive behaviour)

Reporting side effects:

If you experience any side effects, talk to your doctor or pharmacist. You can also report suspected side effects directly via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or search for MHRA Yellow Card in the Google Play or Apple App Store. Reporting helps provide information on the safety of this medicine.

Who Can Use Testogel and When Is It Prescribed?

Testogel is licensed for testosterone replacement therapy in adult males with hypogonadism confirmed by clinical symptoms and biochemical testing. Hypogonadism may be primary (testicular failure) or secondary (hypothalamic-pituitary dysfunction), and can result from congenital conditions (e.g., Klinefelter syndrome), acquired disorders (e.g., chemotherapy, trauma, pituitary disease), or age-related decline.

Diagnostic criteria (as per NICE Clinical Knowledge Summaries and BSSM guidelines) typically require:

• Clinical symptoms: Reduced libido, erectile dysfunction, fatigue, decreased muscle mass, mood disturbances, reduced bone density, or hot flushes

• Biochemical confirmation: Two separate early-morning (before 11:00) serum total testosterone measurements, both below the reference range (typically <8–12 nmol/L, though laboratory thresholds vary). If results are borderline, measurement of sex hormone-binding globulin (SHBG) and calculated free testosterone may be helpful.

Diagnostic work-up should include:

• Serum luteinising hormone (LH) and follicle-stimulating hormone (FSH) to distinguish primary from secondary hypogonadism

• Prolactin (elevated levels may indicate a pituitary tumour)

• Thyroid function tests

• Assessment for underlying causes, including iron overload (ferritin), chronic illness, obesity, and medications

Red-flag features requiring urgent specialist referral (endocrinology or neurosurgery):

• Very low testosterone with low or normal LH/FSH (suggesting pituitary or hypothalamic disease)

• Hyperprolactinaemia

• Visual disturbances, persistent headaches, or other symptoms suggestive of a pituitary mass

• Rapid onset or severe symptoms

Testosterone therapy is not recommended for men with normal testosterone levels seeking performance enhancement, anti-ageing benefits, or treatment of non-specific symptoms, as there is insufficient evidence of benefit and potential for harm.

Specific populations:

• Older men: Age-related testosterone decline (late-onset hypogonadism) is common but not always pathological. Treatment should be individualised, considering symptom severity, comorbidities, and patient preference, following thorough discussion of risks and benefits.

• Fertility considerations: Exogenous testosterone suppresses the hypothalamic-pituitary-gonadal axis and spermatogenesis, rendering men infertile during treatment. Recovery of fertility after stopping TRT may take many months and is not guaranteed. Testogel is contraindicated in men actively seeking to father children. Alternative treatments under specialist care (e.g., human chorionic gonadotrophin [hCG], clomifene citrate) may preserve or restore fertility while addressing hypogonadism.

• Women and children: Testogel is not licensed for use in women or children. Accidental exposure can cause virilisation in women and precocious puberty in children.

Prescribing and shared care:

Treatment is typically initiated by specialists (endocrinologists or urologists) following comprehensive evaluation. Ongoing monitoring may be shared between secondary and primary care according to local shared-care protocols. Patients should be counselled on realistic expectations, potential risks, the critical importance of preventing testosterone transfer to others, the need for adherence, and regular follow-up. Lifestyle modifications—including regular exercise, weight management, smoking cessation, and addressing underlying conditions such as obstructive sleep apnoea—should complement pharmacological therapy and may improve outcomes.

Frequently Asked Questions