Testogel is a prescription testosterone gel used for hormone replacement therapy in men with hypogonadism. Many patients wonder whether Testogel is synthetic and what this means for safety and effectiveness. The testosterone in Testogel is indeed synthetically manufactured in pharmaceutical laboratories, but it is bioidentical to the hormone naturally produced by the body. This means the molecular structure is identical, and the body processes synthetic and endogenous testosterone in exactly the same way. Understanding the nature of synthetic testosterone helps patients make informed decisions about their treatment under medical supervision.

What Is Testogel and How Is It Made?

Testogel is a synthetic testosterone preparation formulated as a transdermal gel for topical application. The active pharmaceutical ingredient is testosterone, chemically identical to the hormone naturally produced by the testes, but manufactured through synthetic processes in pharmaceutical laboratories rather than extracted from biological sources.

The manufacturing process involves chemical synthesis from plant-derived steroid precursors. Through a series of controlled chemical reactions, these precursors are converted into testosterone with the exact molecular structure (C₁₉H₂₈O₂) as endogenous testosterone. This synthetic production ensures consistent purity, potency, and pharmaceutical quality that meets stringent regulatory standards set by the Medicines and Healthcare products Regulatory Agency (MHRA).

In the UK, Testogel is available in two licensed formulations: Testogel 50 mg in 5 g gel (1%) sachets and Testogel 16.2 mg/g metered-dose pump gel (approximately 1.62%). Both contain testosterone suspended in an alcohol-based vehicle with additional excipients including carbomer, isopropyl myristate, and ethanol. These ingredients facilitate transdermal absorption through the skin and into the bloodstream.

Once applied to clean, dry skin, the alcohol evaporates quickly, leaving testosterone to be absorbed gradually over several hours. Application sites differ by formulation: the 1% sachet may be applied to shoulders, upper arms, or abdomen, whilst the 16.2 mg/g pump gel should be applied only to shoulders and upper arms. The gel must not be applied to the genital area or broken or irritated skin. Patients should allow the gel to dry completely, wash their hands thoroughly after application, and cover the application site with clothing. The gel is flammable until dry; patients must avoid fire, flames, and smoking until the gel has dried. To prevent washing off the medication, patients should avoid showering, bathing, or swimming for at least 2 hours after applying the 16.2 mg/g pump gel or 6 hours after applying the 1% sachet.

Testogel is licensed in the UK for testosterone replacement therapy (TRT) in adult males with hypogonadism—a condition where the body produces insufficient testosterone. The synthetic nature of the medication does not diminish its therapeutic efficacy; rather, it ensures reliable dosing, batch-to-batch consistency, and freedom from contaminants. Each pump actuation or sachet delivers a measured dose, allowing for individualised treatment regimens under medical supervision.

How Synthetic Testosterone Works in the Body

Once absorbed through the skin, synthetic testosterone from Testogel functions identically to naturally produced testosterone because the molecular structures are indistinguishable. The body cannot differentiate between endogenous testosterone and the bioidentical synthetic hormone, meaning the physiological effects and metabolic pathways are the same.

Testosterone exerts its effects through binding to androgen receptors located in various tissues throughout the body, including muscle, bone, brain, and reproductive organs. This receptor binding triggers genomic and non-genomic pathways that regulate:

• Protein synthesis and muscle mass maintenance

• Bone mineral density and skeletal health

• Red blood cell production (erythropoiesis)

• Libido and sexual function

• Mood regulation and cognitive function

• Fat distribution and metabolic processes

Following transdermal absorption, testosterone enters the systemic circulation and is distributed to target tissues. Testosterone is converted in peripheral tissues into active metabolites including dihydrotestosterone (DHT) via the 5α-reductase enzyme, and oestradiol through aromatisation. These metabolites contribute to the overall androgenic and oestrogenic effects of testosterone therapy. The liver is primarily responsible for inactivation and clearance of testosterone and its metabolites through conjugation and excretion.

The pharmacokinetic profile of Testogel provides relatively steady serum testosterone levels when applied daily, avoiding the pronounced peaks and troughs associated with short-acting intramuscular testosterone injections. (Long-acting intramuscular testosterone undecanoate can also provide stable levels.) Serum testosterone concentrations typically reach therapeutic ranges within days of initiating treatment, with steady state achieved after several days of consistent application. The gel formulation allows for dose adjustments based on individual response, monitored through regular blood tests.

Monitoring of testosterone levels should be performed according to the product's Summary of Product Characteristics (SmPC) and UK clinical guidance. Blood samples are typically taken in the morning, and timing relative to gel application should follow SmPC recommendations (often pre-dose or at a specified interval after application). Total testosterone is the primary measure; free or calculated free testosterone may be measured in borderline cases or when sex hormone-binding globulin (SHBG) abnormalities are suspected.

Safety and Regulation of Testogel in the UK

Testogel is a prescription-only medicine (POM) in the UK, regulated by the MHRA and subject to rigorous safety and quality standards. It is licensed for use only in men with confirmed hypogonadism, diagnosed through clinical symptoms and biochemical evidence of low testosterone levels.

NICE Clinical Knowledge Summaries (CKS) and the British Society for Sexual Medicine (BSSM) provide UK guidance on diagnosis and management. Before prescribing Testogel, clinicians must:

• Confirm biochemical hypogonadism with two early-morning serum total testosterone measurements using laboratory-specific reference ranges. Typically, levels consistently below 8 nmol/L support a diagnosis of hypogonadism; levels between 8 and 12 nmol/L are borderline and require repeat testing, assessment of SHBG and calculated free testosterone, and careful clinical evaluation.

• Perform baseline investigations including luteinising hormone (LH), follicle-stimulating hormone (FSH), SHBG, prolactin, full blood count, liver function tests, and prostate-specific antigen (PSA) in men over 40 or with risk factors. Consider digital rectal examination (DRE) where clinically indicated. If LH and FSH are low or normal in the presence of low testosterone, or if prolactin is elevated, consider pituitary evaluation.

• Exclude contraindications including known or suspected prostate cancer, male breast cancer, and hypersensitivity to any component of the gel.

• Assess cautions and risk factors including severe cardiac, hepatic, or renal disease, risk of oedema, obstructive sleep apnoea, and cardiovascular risk factors. Discuss potential risks and benefits with the patient.

Ongoing monitoring is essential for patient safety. BSSM guidelines recommend follow-up at 3 months, 6 months, and 12 months, then annually, including:

• Serum testosterone levels (target: mid-normal range for age), measured according to SmPC timing guidance

• Haematocrit monitoring: if haematocrit exceeds 54%, reduce the dose or stop treatment and investigate the cause

• PSA levels in men over 40 or with risk factors; consider DRE per local guidance

• Symptom assessment and treatment response

• Cardiovascular and metabolic parameters

Important safety considerations include the risk of testosterone transfer to others through skin-to-skin contact. Patients must apply Testogel to areas normally covered by clothing, allow the gel to dry completely before dressing, wash hands thoroughly with soap and water immediately after application, and cover the application site with clothing before close physical contact with others, particularly women and children. If accidental transfer occurs, the affected person should wash the contact area immediately with soap and water. The gel is flammable until dry; patients must avoid fire, flames, and smoking during application and until the gel has dried.

Patients should contact their GP promptly if they experience signs of excessive testosterone (severe acne, aggression, sleep disturbance) or adverse effects. Seek urgent medical attention for chest pain, sudden breathlessness, unilateral leg swelling or calf pain (possible signs of blood clots), or any other serious symptoms.

Patients and healthcare professionals are encouraged to report suspected adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Natural vs Synthetic Testosterone: What Patients Should Know

A common misconception is that "natural" testosterone is superior or safer than synthetic testosterone. In reality, the testosterone in Testogel is bioidentical to endogenous testosterone—the molecular structure is identical, and the body processes both in exactly the same way. The term "synthetic" refers to the manufacturing method, not the chemical structure or biological activity. The safety and efficacy of testosterone therapy depend on correct indication, appropriate dosing, and careful monitoring, not on whether the hormone is synthesised in a laboratory or produced by the body.

Some patients enquire about "natural" testosterone products or supplements. It is important to understand that:

• In the UK, any product containing testosterone is a prescription-only medicine and, in many cases, a controlled drug. Over-the-counter products claiming to contain testosterone are not legally available.

• Herbal or "natural" testosterone boosters lack robust evidence for efficacy in treating diagnosed hypogonadism and are not appropriate substitutes for licensed testosterone replacement therapy.

• Compounded or unlicensed "bioidentical" hormones lack the rigorous testing, standardisation, quality assurance, and regulatory oversight of licensed pharmaceutical products such as Testogel.

• Testosterone extracted from animal sources is not used in modern medicine due to concerns about purity, consistency, and safety.

The advantage of pharmaceutical-grade synthetic testosterone like Testogel is precise dosing, consistent quality, and proven safety and efficacy profiles established through extensive clinical trials and regulatory review by the MHRA and European Medicines Agency (EMA).

Patients considering testosterone therapy should have realistic expectations. TRT is not appropriate for:

• Age-related decline in testosterone without confirmed hypogonadism and significant symptoms

• Performance enhancement or bodybuilding

• General fatigue or low mood without biochemical evidence of hypogonadism

• Fertility enhancement: TRT suppresses sperm production and can cause infertility. Men wishing to preserve or achieve fertility should avoid TRT and discuss specialist alternatives (such as gonadotrophin therapy or selective oestrogen receptor modulators) with an endocrinologist or urologist.

Decisions about testosterone therapy should be made collaboratively between patient and clinician, based on confirmed diagnosis, individual circumstances, and careful consideration of benefits and risks. Regular monitoring ensures treatment remains safe and effective, and any concerns should be discussed openly with the prescribing doctor.

Frequently Asked Questions