Testosterone replacement therapy (TRT) is sometimes considered by men experiencing weight gain alongside symptoms of low testosterone. Whilst testosterone plays a role in body composition—influencing muscle mass, fat distribution, and metabolism—its use as a weight loss treatment is not straightforward. TRT may modestly improve body composition in men with clinically confirmed hypogonadism, primarily by reducing visceral fat and increasing lean muscle mass. However, it is not a licensed weight management intervention and should only be prescribed when both biochemical deficiency and clinical symptoms are present. This article examines the evidence linking testosterone treatment to weight changes, who may benefit, associated risks, and alternative approaches to sustainable weight management.

Understanding Testosterone and Body Weight

Testosterone is the primary male sex hormone, though it is also present in smaller quantities in women. Produced mainly in the testes in men and the ovaries in women, testosterone plays a crucial role in numerous physiological processes including muscle mass maintenance, bone density, red blood cell production, and fat distribution. Reference ranges vary by laboratory and assay; adult male early-morning total testosterone is typically ~8-30 nmol/L. Interpret results in context, using sex hormone binding globulin (SHBG) and calculated free testosterone when appropriate.

The relationship between testosterone and body weight is complex and bidirectional. Low testosterone levels (hypogonadism) are associated with increased body fat, particularly visceral adipose tissue around the abdomen, and reduced lean muscle mass. This altered body composition can contribute to weight gain and metabolic dysfunction. Conversely, obesity itself can suppress testosterone production through several mechanisms, including increased aromatase enzyme activity in adipose tissue, which converts testosterone to oestrogen, and inflammation-related disruption of the hypothalamic-pituitary-gonadal axis.

Key factors linking testosterone and weight include:

• Regulation of fat metabolism and storage

• Maintenance of muscle mass, which influences basal metabolic rate

• Impact on insulin sensitivity and glucose metabolism

• Effects on energy levels and physical activity capacity

It is important to recognise that whilst low testosterone may contribute to weight gain, it is rarely the sole cause of obesity. Multiple factors including diet, physical activity, sleep quality, stress, and other medical conditions all play significant roles in weight management. Understanding this relationship helps contextualise the potential role of testosterone therapy in weight loss strategies.

Does Testosterone Treatment Help with Weight Loss?

Testosterone replacement therapy (TRT) may contribute to modest improvements in body composition in men with clinically confirmed hypogonadism, but it is not a standalone weight loss treatment. Clinical evidence suggests that when testosterone levels are restored to normal physiological ranges in hypogonadal men, there can be a reduction in fat mass (particularly visceral fat) and an increase in lean muscle mass. However, these changes do not necessarily translate to significant reductions in overall body weight.

A systematic review of randomised controlled trials found that testosterone therapy in hypogonadal men resulted in an average reduction of approximately 1.6 kg in fat mass and an increase of roughly 1.6 kg in lean mass over 12 months. The net effect on total body weight was therefore minimal, though body composition improved. The magnitude of these effects varies considerably between individuals and depends on factors including baseline testosterone levels, treatment duration, dosage, and concurrent lifestyle modifications.

Important considerations regarding TRT and weight loss:

• Testosterone therapy is only appropriate for men with confirmed hypogonadism (typically two early-morning tests; <8 nmol/L usually low; 8-12 nmol/L borderline—interpret with symptoms and free testosterone)

• It works primarily by improving body composition rather than causing dramatic weight loss

• Effects are most pronounced when combined with resistance exercise and dietary modifications

• There is no official link established between testosterone therapy and guaranteed weight loss in men with normal testosterone levels

For women, testosterone therapy is occasionally used for specific conditions such as hypoactive sexual desire disorder (HSDD) per NICE NG23 guidance, but it is not licensed or recommended for weight loss purposes. The MHRA has not approved testosterone products for weight management in either men or women, and prescribing for this indication alone would be considered off-label use.

Who May Benefit from Testosterone Therapy

Testosterone replacement therapy is a legitimate medical treatment for men with confirmed hypogonadism, not a weight loss intervention for the general population. According to UK clinical guidance, TRT should only be considered in men who have both biochemical evidence of testosterone deficiency and associated clinical symptoms. Diagnosis requires at least two fasting early-morning blood samples (taken between 7am and 11am) showing testosterone levels below the normal range, typically <8 nmol/L is considered low, with 8-12 nmol/L being borderline and requiring clinical correlation.

Clinical features that may indicate hypogonadism include:

• Reduced libido and erectile dysfunction

• Decreased energy levels and persistent fatigue

• Loss of muscle mass and strength

• Increased body fat, particularly around the abdomen

• Mood changes including low mood or irritability

• Reduced bone density (osteoporosis)

• Hot flushes and sweating

Men who may benefit from testosterone therapy include those with primary hypogonadism (testicular failure due to genetic conditions, chemotherapy, or trauma) or secondary hypogonadism (pituitary or hypothalamic disorders). Age-related decline in testosterone is common, but not all older men require treatment—therapy should be based on symptoms and confirmed low levels, not age alone.

Before initiating TRT, comprehensive assessment is essential. This includes measuring luteinising hormone (LH), follicle-stimulating hormone (FSH), SHBG, and prolactin if indicated. Evaluation for contraindications such as prostate cancer, male breast cancer, uncontrolled heart failure, severe untreated sleep apnoea, haematocrit >54%, or desire for fertility is necessary. Baseline investigations typically include prostate-specific antigen (PSA), full blood count, and liver function tests. Men with obesity-related hypogonadism should first be encouraged to lose weight through lifestyle modifications, as this alone may restore testosterone levels to normal ranges.

Referral to an endocrinologist or urologist is appropriate for men with markedly low testosterone with inappropriately low/normal gonadotropins, raised prolactin, pituitary symptoms (headache, visual disturbance), or testicular abnormalities.

It is crucial to understand that testosterone therapy is not appropriate for men with normal testosterone levels seeking weight loss or athletic enhancement. Such use carries risks without proven benefits and is not supported by clinical guidelines.

Risks and Side Effects of Testosterone Treatment

Testosterone replacement therapy, whilst beneficial for appropriately selected patients, carries potential risks and side effects that require careful monitoring. The MHRA and EMA have issued guidance on the safe use of testosterone products, emphasising the importance of proper patient selection and ongoing surveillance.

Common side effects of testosterone therapy include:

• Acne and oily skin

• Fluid retention and ankle swelling

• Breast enlargement (gynaecomastia)

• Testicular atrophy and reduced sperm production

• Sleep apnoea (worsening of existing condition)

• Mood changes and increased aggression

• Injection site reactions (for intramuscular preparations)

More serious potential risks include:

Cardiovascular effects: There has been ongoing debate regarding testosterone therapy and cardiovascular risk. Some studies have suggested potential increased risk of cardiovascular events, particularly in older men with pre-existing heart disease. The MHRA advises caution in men with significant cardiovascular risk factors or severe cardiac, hepatic or renal disease. Patients should be counselled to seek urgent medical attention for chest pain, shortness of breath, unilateral leg swelling, or neurological deficits.

Polycythaemia: Testosterone stimulates red blood cell production, which can lead to elevated haematocrit levels. This increases blood viscosity and potentially raises the risk of thrombotic events. If haematocrit exceeds ~54%, pause or reduce dose and investigate (e.g., sleep apnoea, smoking); consider venesection if needed. Regular monitoring of full blood count is essential, typically every 3-6 months initially, then annually once stable.

Prostate concerns: Whilst testosterone does not cause prostate cancer, it may accelerate growth of existing disease. PSA levels and prostate examination should be monitored regularly, particularly in men over 50 or those with risk factors for prostate cancer. Refer according to NICE NG12 if PSA is above age-specific range or if digital rectal examination is abnormal.

Fertility implications: Testosterone therapy suppresses the hypothalamic-pituitary-gonadal axis, reducing sperm production and potentially causing infertility. Men wishing to father children should discuss alternative treatments or fertility preservation options before starting therapy.

Gel transfer precautions: For transdermal preparations, apply to clean, dry skin; wash hands; allow to dry; cover site; avoid skin-to-skin contact until dry; observe product-specific SmPC advice to prevent transfer to women and children.

Patients receiving testosterone therapy require regular monitoring including clinical review at 3-6 months then annually, aiming for mid-normal physiological testosterone levels, with full blood count, PSA, and liver function tests. Any concerning symptoms should prompt immediate contact with a GP or specialist. Patients should report suspected side effects via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

Alternative Weight Loss Approaches and Lifestyle Changes

For most men concerned about weight gain and low energy—whether or not they have confirmed hypogonadism—evidence-based lifestyle modifications remain the cornerstone of effective weight management. These approaches are safer, more sustainable, and often more effective than pharmacological interventions alone.

Dietary modifications: A balanced, calorie-controlled diet is fundamental to weight loss. NICE recommends aiming for a deficit of 600 kcal per day to achieve gradual, sustainable weight loss of 0.5-1 kg per week. Focus should be on whole foods including vegetables, fruits, lean proteins, whole grains, and healthy fats, whilst limiting processed foods, sugary beverages, and excessive alcohol. For men with obesity and related metabolic complications, referral to NHS Tier 2 or Tier 3 weight management services may be beneficial.

Physical activity: Regular exercise is crucial for both weight loss and improving testosterone levels naturally. UK Chief Medical Officers' guidelines recommend at least 150 minutes of moderate-intensity aerobic activity weekly, combined with resistance training on two or more days. Resistance exercise is particularly important as it helps build and maintain muscle mass, which increases metabolic rate and may naturally support testosterone production. Even modest increases in physical activity can yield significant health benefits.

Sleep optimisation: Poor sleep quality and insufficient sleep duration (less than 7 hours nightly) are associated with both weight gain and reduced testosterone levels. Addressing sleep disorders such as obstructive sleep apnoea—common in men with obesity—can improve both metabolic health and hormonal balance.

Stress management: Chronic stress elevates cortisol levels, which can promote abdominal fat accumulation and suppress testosterone production. Stress reduction techniques including mindfulness, cognitive behavioural approaches, and regular physical activity may help.

Medical review: Certain medications (such as opioids, corticosteroids, or some antidepressants) can affect weight and testosterone levels. A medication review with a GP may identify modifiable factors. Additionally, screening for other conditions that affect weight and metabolism—including thyroid disorders, diabetes, and depression—is important.

Medical treatments for obesity: For those with BMI ≥30 kg/m² (or ≥27 kg/m² with weight-related comorbidities), NICE-approved treatments may be considered alongside lifestyle changes. These include orlistat and, where commissioned, GLP-1 receptor agonists such as semaglutide (per NICE TA875). Bariatric surgery may be considered for those with BMI ≥40 kg/m² or ≥35 kg/m² with weight-related conditions, per NICE guidance.

When to seek medical advice: Consult a GP if experiencing persistent fatigue, significant unexplained weight changes, reduced libido, or other symptoms suggestive of hormonal imbalance. Seek urgent medical attention for red flags such as unintentional weight loss, rectal bleeding, persistent vomiting, or symptoms of diabetes (excessive thirst/urination). If considering testosterone therapy, ensure proper evaluation including blood tests and discussion of risks and benefits. Remember that for men with obesity-related low testosterone, weight loss through lifestyle changes alone often restores testosterone levels without need for hormone therapy.

Frequently Asked Questions