Clinical Insight | Men's Health Series — Wildberry Clinic

Can testosterone restore youthful energy, libido, muscle mass and vitality? Or could replacing it without understanding the underlying physiology create more problems than it solves?

Key points

• Low libido, fatigue and abdominal weight gain are nonspecific. Neither age nor symptoms alone confirm testosterone deficiency.
• A single low total testosterone result is not a diagnosis. Time of day, food, sleep, illness and SHBG can all shift the number.
• Diagnosis needs consistently low morning results alongside compatible symptoms, followed by tests to find the cause.
• Testosterone treatment can suppress the body's own testosterone production and, in many men, fertility.
• Replacement is valuable for confirmed hypogonadism. The evidence does not support it as a general anti-ageing therapy.

Testosterone has become one of the most talked-about hormones in the growing anti-ageing and longevity market. Testosterone replacement therapy (TRT), traditionally prescribed for clinically confirmed male hypogonadism, is increasingly promoted as a way to restore vitality, sexual performance, physical strength and the body composition of younger years.

The appeal is understandable. As men age, changes in libido, energy, muscle mass and abdominal fat distribution may coincide with a gradual decline in circulating testosterone. The proposed solution seems straightforward: if testosterone has fallen, replace it.

But declining testosterone does not necessarily represent a deficiency requiring treatment, and raising circulating testosterone does not necessarily restore the functions that change with age. The distinction between correcting hypogonadism and attempting to reverse ageing is fundamental.

Is testosterone deficiency really the problem?

Testosterone is essential for male reproductive and sexual function, and contributes to the maintenance of muscle, bone, erythropoiesis and other androgen-responsive tissues.

Nevertheless, the symptoms commonly attributed to declining testosterone are remarkably nonspecific. Reduced libido, fatigue, poor motivation, increased abdominal adiposity, reduced physical performance and disturbed sleep may occur in men with hypogonadism. They may equally arise from metabolic dysfunction, psychological factors, medication effects, chronic illness, poor sleep or other endocrine disturbances.

Age-related changes are not uniform either. Some men maintain adequate testosterone concentrations well into older age, while others experience reductions associated with obesity, comorbidities or impaired testicular and hypothalamic–pituitary function.

Consequently, neither chronological age nor the presence of these symptoms is sufficient to establish testosterone deficiency. Even a blood test reporting low testosterone requires careful interpretation.

A carefully regulated system

Testosterone production is tightly controlled by a feedback loop between the brain and the testes, known as the hypothalamic–pituitary–testicular (HPT) axis. The hypothalamus releases gonadotrophin-releasing hormone (GnRH), which stimulates the anterior pituitary to secrete luteinising hormone (LH) and follicle-stimulating hormone (FSH). LH stimulates the Leydig cells of the testes to produce testosterone. FSH supports Sertoli-cell function and spermatogenesis, which also depends on the very high intratesticular testosterone concentrations required for sperm production.

Testosterone and its metabolite oestradiol feed back negatively on the hypothalamus and pituitary, while inhibin B contributes to the regulation of FSH. The system continuously adjusts output in response to endocrine and physiological signals.

A reduction in circulating testosterone may therefore reflect dysfunction at several different levels. The testes may be unable to produce adequate testosterone despite appropriate stimulation. The hypothalamus or pituitary may be providing insufficient stimulation. Or systemic illness, metabolic dysfunction or other potentially reversible factors may be suppressing the axis.

These situations call for different clinical approaches. Before replacing testosterone, we must establish whether the problem lies in the testes, in their regulatory signals, or in the broader physiological environment.

Why can a testosterone blood test appear low?

A single low result is not equivalent to a diagnosis of hypogonadism. Testosterone concentrations fluctuate from day to day and across the circadian cycle, and several factors influence what a test actually measures.

• Poor sleep, shift work, sleep disorders: can lower morning testosterone; a sample taken after a bad night may not reflect usual status.
• Time of day: levels are highest in the morning, particularly in younger men.
• Recent food or glucose: can temporarily lower testosterone, hence the preference for fasting samples.
• Acute illness, undernutrition, energy restriction, overtraining: can suppress reproductive hormone signalling.
• Obesity and insulin resistance: often lower SHBG, reducing total testosterone; may also suppress the HPT axis.
• Liver or thyroid disease, some medications: alter SHBG, shifting total testosterone independently of free testosterone.
• 
  

Two of these deserve a closer look.

Metabolic health. One of the most important considerations is the relationship between testosterone, obesity and insulin resistance. In men with abdominal obesity or metabolic dysfunction, sex hormone-binding globulin (SHBG) is frequently reduced. Because most circulating testosterone is bound to SHBG or albumin, lower SHBG can reduce measured total testosterone without a matching fall in free testosterone. In other men, significant obesity-associated metabolic dysfunction suppresses HPT axis activity, lowering free as well as total testosterone. A low total result may therefore represent altered binding, genuinely reduced production, or both.

Liver and thyroid function. SHBG is produced primarily by the liver, and its concentration is influenced by hepatic function, thyroid status and certain medications. Hyperthyroidism can raise SHBG, whereas obesity, insulin resistance and hypothyroidism are commonly associated with lower levels. This makes total testosterone alone potentially misleading.

Psychological stress also affects sleep, behaviour and endocrine function, although it should not be assumed to explain every low result.

What investigations justify testosterone replacement?

Male hypogonadism should be diagnosed on the basis of compatible clinical features and consistently low testosterone, not on symptoms or a single laboratory value in isolation.

Two separate morning measurements, preferably fasting and taken when the patient is clinically stable, are generally required. Guidelines differ in their cut-offs, but in broad terms a total testosterone below roughly 8 nmol/L is regarded as clearly low, while values between about 8 and 12 nmol/L are borderline and need interpretation alongside symptoms, SHBG and free testosterone.

When total testosterone is borderline or SHBG may be abnormal, free testosterone should be assessed by a reliable method, such as equilibrium dialysis or a validated calculation based on total testosterone, SHBG and albumin.

Once deficiency is confirmed, LH and FSH help establish its origin. Low testosterone with elevated LH suggests primary testicular dysfunction. Low testosterone with low or inappropriately normal LH suggests secondary hypogonadism, which may arise from hypothalamic–pituitary disease or functional suppression. FSH adds information about Sertoli-cell and spermatogenic function.

Depending on the presentation, further investigation may include prolactin, HbA1c, fasting glucose, thyroid function, lipid profile, liver and renal function, iron studies and additional pituitary tests. Pituitary imaging is indicated in selected cases, particularly with severe secondary hypogonadism, persistent hyperprolactinaemia or symptoms suggesting a pituitary lesion.

The goal is not to order every available hormone test. It is to identify the mechanism behind the deficiency and to decide whether it is persistent, pathological and potentially reversible.

What happens when testosterone is replaced?

Testosterone can be given as a transdermal gel, an intramuscular injection or other preparations, depending on the country and the licensed product. In the UK and Ireland, for example, testosterone gel is a prescription-only medicine, commonly applied daily to designated areas of skin.

Once absorbed, external testosterone contributes to circulating androgen concentrations. But the endocrine system responds to its presence. Testosterone, and the oestradiol derived from it, exert negative feedback on the hypothalamus and pituitary. GnRH stimulation falls, LH and FSH may drop substantially, and the testes reduce their own testosterone production.

In other words, replacing testosterone can suppress the body's own testosterone-producing system.

For men with irreversible testicular failure, this is a necessary and appropriate consequence of effective replacement. For men whose hormonal production was potentially recoverable, it raises a different question: have we supported physiological recovery, or simply replaced one form of regulation with pharmacological exposure?

The fertility trade-off

One of the most important and frequently underappreciated consequences of testosterone treatment concerns male fertility.

Normal sperm production requires adequate FSH signalling and very high intratesticular testosterone. External testosterone can suppress both LH and FSH, so intratesticular testosterone falls and sperm production may be significantly impaired. Some men develop severe oligospermia or azoospermia, meaning very few or no sperm in the ejaculate, and testicular volume may also decrease.

Recovery after stopping is possible, but it can take months or longer and the timing is not always predictable. A man can therefore have normal or elevated circulating testosterone while his own testicular function and fertility are substantially suppressed.

This matters greatly for men who may wish to father children. For some men with secondary hypogonadism, specialist-led alternatives that stimulate the body's own production can be considered, which is one more reason the cause of low testosterone needs to be established before treatment begins.

Other consequences of inappropriate treatment

Testosterone is a biologically active hormone, not an innocuous nutritional supplement.

One established adverse effect is erythrocytosis, a rise in red blood cell concentration and haematocrit that may require dose adjustment, interruption or further assessment. Other effects can include acne, fluid retention, breast tenderness, gynaecomastia and worsening of certain pre-existing conditions.

Testosterone may increase blood pressure, and men with significant cardiovascular risk, a history of thromboembolism or relevant haematological abnormalities need careful evaluation. Untreated severe obstructive sleep apnoea, elevated haematocrit and certain prostate or breast conditions must also be considered.

Testosterone gel adds the possibility of transferring medication through skin contact to partners or children.

These risks do not make replacement inherently unsafe. They mean that prescribing requires an established indication, appropriate dosing and continuing clinical monitoring, which unregulated online clinics and private sources are unlikely to provide.

Does testosterone reverse ageing?

The anti-ageing argument rests partly on the observation that testosterone often declines with age. But ageing is not simply the progressive disappearance of one hormone. It involves interconnected changes in mitochondrial energetics, insulin sensitivity, vascular function, inflammatory regulation, skeletal muscle, bone, sleep architecture and neuroendocrine signalling. Testosterone participates in several of these systems, but it does not independently control them.

Clinical research shows that replacement can improve sexual desire and some other outcomes in appropriately selected men with low testosterone. It may increase lean body mass and reduce fat mass, although these changes do not consistently translate into substantial gains in strength or physical performance. Evidence that testosterone improves general vitality, cognitive function or overall ageing outcomes is considerably weaker.

The 2026 European Association of Urology guidelines specifically advise against using testosterone in men with normal gonadal function, and against prescribing it solely to improve cognition, vitality or physical strength in ageing men. They also do not recommend it as a weight-loss or general cardiometabolic treatment.

Restoring a youthful hormone concentration is not the same as restoring youthful physiological function.

What does the cardiovascular evidence tell us?

The large TRAVERSE randomised trial examined cardiovascular safety in men with symptoms and biochemical evidence of hypogonadism who also had pre-existing cardiovascular disease or elevated cardiovascular risk. Major adverse cardiovascular events occurred in 7.0% of testosterone-treated participants and 7.3% of the placebo group, meeting the trial's criterion for noninferiority.

However, atrial fibrillation, pulmonary embolism and acute kidney injury were more frequent in the testosterone group, and fractures were also more common. Follow-up was under two years on average.

The findings are reassuring about major cardiovascular outcomes in the studied population under monitored treatment. They do not establish unrestricted, long-term safety for healthy men pursuing testosterone as an anti-ageing strategy.

Regulatory perspectives are also evolving. In 2026, the US FDA requested changes to testosterone product labelling concerning age-related hypogonadism and prostate-related safety information. This may broaden discussion of treatment eligibility, but it does not make testosterone a therapy that reverses biological ageing, nor does it remove the need for accurate diagnosis and safety monitoring.

When is testosterone a friend?

Testosterone replacement is an important medical treatment for men with appropriately confirmed, symptomatic hypogonadism. Men with irreversible primary testicular failure, for example, may need it to maintain normal androgen-dependent function. Selected men with secondary hypogonadism may also benefit, depending on the cause, fertility considerations and alternative treatments.

In appropriately selected patients, it can improve sexual symptoms, correct certain consequences of androgen deficiency and help maintain muscle and bone health. Treatment should be individualised, aiming for physiological concentrations rather than indiscriminately high levels. Monitoring includes symptoms, testosterone concentrations, haematocrit, blood pressure, adverse effects and age- and risk-appropriate prostate assessment.

And when does it become a foe?

Problems arise when testosterone is used without a confirmed clinical indication, when the cause of low levels has not been investigated, or when the expected benefits extend far beyond what the evidence supports.

A man with obesity-associated low SHBG may not need replacement simply because his total testosterone looks low. A man with medication-related or metabolic suppression may need the contributing condition treated. A man with secondary hypogonadism from pituitary disease needs investigation and treatment far beyond raising testosterone. And a man seeking more energy, less abdominal fat or a return to youthful performance may find that testosterone does not resolve the underlying reasons for his symptoms.

In such circumstances, treatment can introduce new risks while leaving the original disturbance unaddressed.

What to address first

For many men with borderline results or nonspecific symptoms, the most productive steps lie upstream of a prescription:

• Weight and metabolic health. Losing excess abdominal fat and improving insulin sensitivity can raise testosterone and SHBG, and benefits metabolic health in its own right.
• Sleep. Treating poor sleep and screening for sleep apnoea may improve both symptoms and hormone measurements.
• Training and nutrition. Resistance exercise, adequate protein and avoiding prolonged energy restriction or overtraining support hormonal and muscle health.
• Alcohol and medications. Excess alcohol and some prescribed drugs can suppress testosterone and are worth reviewing.
• A proper reassessment. Repeat morning fasting bloods once these factors are addressed, rather than relying on a single result.

Men also frequently ask about over-the-counter "testosterone boosters" and herbal products. The evidence for these is limited, often drawn from small, short trials, and the products are inconsistently regulated, with some containing undeclared ingredients. They are not a substitute for investigation, and anyone taking them should tell their practitioner.

The wider question: treating ageing, or treating an endocrine disorder?

The popularity of testosterone as an anti-ageing intervention reflects a broader tendency to interpret age-related change through individual biomarkers. When a hormone concentration falls, it is tempting to assume that returning it to a youthful value must be beneficial. Yet hormone production, transport, receptor responsiveness, cellular metabolism and downstream tissue function all matter. A single number cannot tell us whether the system is functioning appropriately.

In some men, low testosterone is genuine endocrine disease that requires replacement. In others, it is associated with altered metabolic health, disrupted sleep, systemic illness or changes in binding proteins. Successful treatment depends on understanding which, not simply on correcting the measured value.

Beyond testosterone: our clinical approach to men's hormonal health

When a man presents with reduced libido, fatigue, weight gain or a blood test showing low testosterone, our first objective is not simply to raise his testosterone concentration. It is to understand why he is experiencing these changes.

A low result is one piece of information within a much larger physiological picture. Before assuming that replacement is necessary, we need to establish whether it represents genuine hypogonadism, a temporary change in hormone production, altered hormone binding, or a manifestation of wider metabolic or systemic dysfunction. Our starting point is a comprehensive assessment of the patient's health, not an isolated laboratory value.

A comprehensive physiological assessment

At Wildberry Clinic, we begin by examining the factors that may influence hormonal regulation and overall wellbeing:

• Sleep and circadian regulation: sleep duration, quality and regularity, snoring, daytime fatigue and irregular working hours. Disrupted sleep can affect testosterone regulation, glucose metabolism, appetite, energy and sexual function, and obstructive sleep apnoea is particularly important in men with abdominal weight gain and persistent fatigue.
• Stress and recovery: chronic psychological stress, occupational demands, emotional wellbeing and the balance between physical activity and recovery. Stress-related changes in sleep, appetite and behaviour may contribute to symptoms commonly attributed to low testosterone.
• Glucose regulation and metabolic health: abdominal weight gain, insulin resistance and altered glucose regulation. We consider whether the hormonal findings reflect a broader metabolic disturbance, with reduced SHBG or functional suppression of the HPT axis, rather than permanent testicular dysfunction.
• Physical activity and muscle health: habitual activity, resistance exercise, cardiovascular fitness, strength and recovery. Inactivity and increased adiposity can undermine metabolic health and performance, while excessive training with inadequate nutrition or recovery can suppress reproductive endocrine function.
• Nutrition, liver function and general health: dietary patterns, protein and energy intake, alcohol, medications, possible nutritional deficiencies, liver health, thyroid function and chronic illness, all of which can influence hormone production, metabolism and SHBG.
• Sexual health and psychological wellbeing: low libido needs its own assessment, because sexual desire is shaped by hormonal, neurological, psychological, relational and general health factors. We distinguish reduced desire from erectile dysfunction, fatigue, depression and medication-related sexual side effects. Not every change in sexual function is caused by testosterone deficiency.

Appropriate investigations

Following the clinical assessment, further tests may be recommended through the patient's GP or a relevant medical specialist. The choice depends on the clinical findings rather than an identical panel for every patient.

• Repeat morning fasting total testosterone: establishes whether the low concentration is persistent rather than an isolated finding.
• SHBG and albumin: evaluate hormone-binding status and support free testosterone calculation.
• Free testosterone, when indicated: clarifies androgen status when total testosterone is borderline or SHBG is abnormal.
• LH and FSH: assess HPT axis regulation and distinguish primary from secondary dysfunction.
• Prolactin: investigates selected causes of secondary hypogonadism and sexual symptoms.
• HbA1c and fasting glucose: assess glucose regulation, with HbA1c reflecting average exposure over roughly three months.
• Lipid profile: assesses cardiovascular and metabolic risk.
• Liver function tests and renal function: evaluate hepatic and kidney health and possible systemic contributors.
• TSH and free T4, where indicated: investigate possible thyroid dysfunction.
• Full blood count: assesses anaemia and other haematological abnormalities.
• Iron studies, where indicated: investigate iron overload as a cause of secondary hypogonadism.

The assessment may also include blood pressure, waist circumference, BMI, medication review and screening for obstructive sleep apnoea. Where results suggest significant pituitary dysfunction, primary testicular failure or another endocrine disorder, specialist investigation is necessary.

If the patient is already taking testosterone, his current results may reflect the effects of treatment rather than his original endogenous production. Reviewing pre-treatment investigations and the prescribing history then becomes essential.

Understanding the cause before choosing the treatment

The findings may reveal several quite different situations:

• genuinely impaired testicular production, requiring appropriate medical replacement;
• secondary hypogonadism caused by a pituitary disorder, requiring further investigation;
• low total testosterone associated with obesity, insulin resistance and reduced SHBG, without the same degree of free testosterone deficiency;
• disrupted sleep, chronic fatigue, poor conditioning or metabolic dysfunction contributing to symptoms, with no confirmed pathological hypogonadism.

These men may present with similar complaints, but their therapeutic needs are not the same. The purpose of investigation is to distinguish between them before deciding what intervention is appropriate.

Restoring physiological function

When pathological hypogonadism has not been established, our priorities shift towards the identifiable contributors to poor health and diminished function: improving sleep and circadian regularity, addressing metabolic dysfunction, supporting healthier body composition, developing appropriate activity and recovery patterns, and managing underlying medical conditions.

Where obesity-associated functional suppression is present, better metabolic health and weight management may also improve endogenous testosterone. But the objective is wider than the hormone. Better glucose regulation, cardiovascular health, muscular function, sleep quality and resilience have value whether or not a particular concentration changes.

The role of herbal medicine

Herbal medicine offers a broad range of therapeutic possibilities within an individualised approach to supporting health and physiological function. Rather than choosing plants for their reputation as testosterone boosters, we assess the clinical picture and identify the systems that need attention, which may include sleep and stress-related symptoms, digestive and metabolic health, recovery and general wellbeing.

The choice of botanical treatment is guided by the patient's presentation, medical history, current medication, relevant investigations and the available evidence for both efficacy and safety. Herbal medicines are biologically active and not inherently free of risk. They may have contraindications and interactions, and they should not delay necessary investigation or replace medically indicated hormone therapy.

The purpose is not to substitute a herbal testosterone booster for testosterone gel. It is to address the patient's actual therapeutic needs rather than treat a laboratory number in isolation.

A different clinical objective

Not every man experiencing weight gain, diminished libido or declining vitality has hypogonadism, and not every low result indicates a permanent inability to produce the hormone. When the underlying problem is a potentially reversible disturbance, correcting it may be more appropriate than introducing external testosterone. Our approach is therefore to investigate first, understand the patient's wider health picture and identify the interventions most likely to improve function.

This is not an argument against testosterone replacement. It is an argument for accurate diagnosis, appropriate treatment and respect for the complexity of endocrine regulation. Our objective is not to make a man's testosterone resemble that of his younger years, but to help him achieve the best physiological function and health possible at his present stage of life.

Friend or foe?

Testosterone is neither a miracle anti-ageing intervention nor an inherently dangerous treatment. It is an essential hormone and a valuable therapeutic agent when used for the right clinical indication. The difficulty arises when an established replacement therapy is marketed as a general solution to the complex biology of ageing.

Before replacing a hormone, we should understand why its production has changed, whether the change represents genuine deficiency, and what physiological regulation we may disrupt by intervening.

Because the objective of good medicine is not to recreate the laboratory values of youth. It is to preserve and restore physiological function: safely, appropriately and for the right reasons.

If you are concerned about low energy, libido or mood, the first step is a proper assessment, with morning fasting blood tests repeated if low, not a prescription.

References

1. European Association of Urology (EAU). (2026). EAU Guidelines on Sexual and Reproductive Health: Male Hypogonadism.
   https://uroweb.org/guidelines/sexual-and-reproductive-health/chapter/male-hypogonadism
2. Bhasin, S., Brito, J. P., Cunningham, G. R., et al. (2018). Testosterone therapy in men with hypogonadism: An Endocrine Society clinical practice guideline. The Journal of Clinical Endocrinology & Metabolism, 103(5), 1715–1744.
   https://doi.org/10.1210/jc.2018-00229
3. Snyder, P. J., Bhasin, S., Cunningham, G. R., et al. (2016). Effects of testosterone treatment in older men. The New England Journal of Medicine, 374, 611–624.
   https://doi.org/10.1056/NEJMoa1506119
4. Lincoff, A. M., Bhasin, S., Flevaris, P., et al. (2023). Cardiovascular safety of testosterone-replacement therapy. The New England Journal of Medicine, 389, 107–117.
   https://doi.org/10.1056/NEJMoa2215025
5. Shenoy, M. T., Mondal, S., Fernandez, C. J., & Pappachan, J. M. (2024). Management of male obesity-related secondary hypogonadism: A clinical update. World Journal of Experimental Medicine, 14(2), 93689.
   https://doi.org/10.5493/wjem.v14.i2.93689
6. Leproult, R., & Van Cauter, E. (2011). Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA, 305(21), 2173–2174.
   https://doi.org/10.1001/jama.2011.710
7. American Urological Association (AUA) & American Society for Reproductive Medicine (ASRM). (2024). Diagnosis and Treatment of Infertility in Men: AUA/ASRM Guideline, Amended 2024.
   https://www.auanet.org/guidelines-and-quality/guidelines/male-infertility
8. U.S. Food and Drug Administration (FDA). (2026). Testosterone Information: Regulatory and Prescribing Updates.
   https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/testosterone-information
9. European Association of Urology (EAU). (2026). EAU Guidelines on Sexual and Reproductive Health: Male Infertility.
   https://uroweb.org/guidelines/sexual-and-reproductive-health/chapter/male-infertility

Disclaimer

This article is for clinical education and does not replace individual medical assessment. Testosterone treatment should only be initiated, adjusted or discontinued under appropriate medical supervision.