Testosterone (Low Testosterone & TRT)
Symptoms, Causes & Treatment
Everything you need to know about testosterone: what it does, what causes low levels, how it is diagnosed, and the effective treatment options available including Testosterone Replacement Therapy (TRT).
What Is Testosterone & What Does It Do?
Testosterone is the principal male sex hormone (androgen), produced primarily in the testes under the regulation of the hypothalamic-pituitary axis. It plays a central role in the development and maintenance of male reproductive tissues and secondary sexual characteristics, as well as having wide-ranging effects on muscle mass, bone density, red blood cell production, mood, cognitive function, energy levels, and libido.
Testosterone deficiency – also known as hypogonadism, androgen deficiency, or colloquially as "low T" – occurs when the testes fail to produce sufficient testosterone to maintain normal physiological function. In the UK, the reference range for total testosterone in adult men is typically 8–30 nmol/L, though symptoms of deficiency can occur across this range, particularly in the lower portion.
Testosterone levels peak in early adulthood and decline gradually with age at an average rate of approximately 1–2% per year after the age of 30–35. While this age-related decline is a natural biological process, some men experience a steeper decline or have levels that fall into a range associated with clinically significant symptoms – sometimes referred to as late-onset hypogonadism (LOH) or andropause, though the latter term is somewhat controversial.
Testosterone deficiency is classified as:
Primary hypogonadism – arising from a problem in the testes themselves (e.g. Klinefelter syndrome, orchitis, testicular injury or torsion, chemotherapy or radiotherapy).
Secondary hypogonadism – arising from a problem in the hypothalamus or pituitary gland that reduces the hormonal signals that stimulate testosterone production (e.g. hyperprolactinaemia, hypothalamic-pituitary tumours, haemochromatosis, opioid use).
Late-onset hypogonadism – age-related testosterone decline in older men, compounded by obesity, chronic illness, and other lifestyle factors.
What Are the Symptoms of Low Testosterone?
Low testosterone (hypogonadism) affects multiple body systems. Symptoms develop gradually and are often attributed to ageing or lifestyle factors, delaying diagnosis by months or years. Symptoms typically appear across physical, sexual, and psychological domains.
Reduced libido (sex drive) · Erectile dysfunction · Fatigue and persistently low energy · Reduced muscle mass and strength · Increased body fat, particularly around the abdomen · Low mood, depression, or irritability · Poor concentration and brain fog · Reduced bone density · Decreased body and facial hair · Reduced semen volume · Small or softer testes · Sleep disturbances · Hot flushes and sweating · Gynaecomastia (breast tissue enlargement)
Symptoms of bone fracture due to low bone density · Severe depression or suicidal ideation · Infertility or inability to conceive after trying for 12 months · Symptoms of pituitary tumour: persistent headache, visual disturbance, or milky nipple discharge · Sudden-onset erectile dysfunction with chest pain or cardiovascular symptoms — seek emergency care immediately
Seek urgent medical attention if you experience symptoms of a pituitary tumour alongside low testosterone: severe persistent headache, sudden visual disturbance, or milky nipple discharge. If you are experiencing severe depression or suicidal thoughts in the context of hormonal changes, contact a clinician or crisis service immediately.
What Causes Low Testosterone?
Testosterone deficiency can arise from problems within the testes themselves (primary hypogonadism), from failure of the pituitary or hypothalamus to stimulate testosterone production (secondary hypogonadism), or from a combination of both. Identifying the underlying cause is essential to guide the most appropriate treatment.
Testosterone production naturally declines by approximately 1–2% per year after the age of 30–40. This gradual decline is normal but can become clinically significant in some men, resulting in symptomatic hypogonadism.
The testes fail to produce adequate testosterone due to conditions such as Klinefelter syndrome, undescended testes, trauma, orchitis, or chemotherapy. The problem lies in the testes themselves.
The pituitary gland or hypothalamus fails to send the correct hormonal signals to the testes. Causes include pituitary tumours, hyperprolactinaemia, Kallmann syndrome, and haemochromatosis.
Excess adipose (fat) tissue converts testosterone to oestrogen via aromatase. Obesity is strongly associated with low testosterone and the relationship is bidirectional — low testosterone promotes fat accumulation.
Conditions such as type 2 diabetes, chronic kidney disease, liver disease, HIV, and sleep apnoea can suppress testosterone. Opioids, glucocorticoids, and certain antihypertensives are common iatrogenic causes.
Exogenous testosterone or anabolic steroid use suppresses the body's natural production via negative feedback on the hypothalamic-pituitary axis, often leading to severe hypogonadism upon cessation.
Key Risk Factors
How Is Low Testosterone Diagnosed?
Diagnosis of testosterone deficiency requires a combination of symptom assessment and blood testing. UK clinical guidance recommends that hypogonadism is only diagnosed when both low testosterone levels and relevant symptoms are present. Blood tests should ideally be taken in the morning (between 8–10am) when testosterone levels are at their highest, and confirmed on at least two separate occasions before treatment is initiated.
How Is Low Testosterone Treated?
Testosterone Replacement Therapy (TRT) is the cornerstone of treatment for confirmed symptomatic hypogonadism. TRT is available in several formulations, each with advantages and considerations. The choice of preparation depends on patient preference, lifestyle, fertility wishes, and clinical factors. All TRT requires ongoing monitoring by a licensed clinician.
Supportive Measures
Alongside TRT, lifestyle optimisation is an important part of managing testosterone deficiency. Regular resistance exercise, achieving and maintaining a healthy weight, improving sleep quality (including treating sleep apnoea), reducing alcohol intake, and managing stress and mental health conditions all support testosterone levels and enhance the response to TRT.
Men on TRT require regular blood monitoring including haematocrit, PSA (age-dependent), lipid profile, and testosterone levels — typically at 3 months initially and every 6–12 months thereafter once stable.
If TRT Is Not Working
If symptoms do not improve after 3–6 months of adequately dosed TRT, several possibilities should be considered: suboptimal dosing, poor compliance with the chosen preparation, incorrect diagnosis, or an unaddressed contributing factor such as obesity, sleep apnoea, or depression. Switching to a different formulation may improve outcomes. If secondary hypogonadism is confirmed, alternative approaches such as hCG or clomiphene may be more appropriate. A specialist endocrinology or urology referral should be considered for complex or treatment-resistant cases.
When Should You Seek Medical Advice About Testosterone?
You experience sudden severe headache with visual disturbance or vomiting suggesting a pituitary emergency · You are experiencing active suicidal ideation related to severe hormonal depression · You have chest pain or signs of cardiovascular event in the context of TRT use (polycythaemia risk).
You are experiencing multiple symptoms of low testosterone including fatigue, low libido, and low mood · You are currently on TRT and experiencing side effects such as polycythaemia symptoms (headache, flushing, visual changes) or worsening prostate symptoms · You have stopped TRT abruptly and are experiencing a hormonal crash · You wish to start TRT but have concerns about fertility · Symptoms of hypogonadism are significantly affecting your quality of life or mental health.
How Can You Support Healthy Testosterone Levels?
While testosterone naturally declines with age and some causes of hypogonadism are not preventable, a number of lifestyle factors have a meaningful and evidence-based impact on testosterone levels. Addressing these can delay the need for TRT or enhance its effectiveness once started.
Obesity is one of the most significant reversible causes of low testosterone. Losing even 5–10% of body weight can meaningfully increase testosterone levels in overweight men.
Resistance training and high-intensity interval training (HIIT) are particularly effective at boosting testosterone. Aim for at least 3 sessions of resistance exercise per week.
The majority of testosterone is produced during deep sleep. Consistently sleeping 7–9 hours per night and treating sleep apnoea where present can significantly improve testosterone levels.
Chronic alcohol use and opioid medications both suppress testosterone production. Reducing or eliminating alcohol and using opioids only as clinically necessary supports hormonal health.
Chronic psychological stress elevates cortisol, which directly suppresses testosterone. Regular relaxation, exercise, good sleep, and addressing mental health conditions all support hormone balance.
Effective management of type 2 diabetes, thyroid disorders, and other chronic conditions helps prevent the secondary testosterone suppression they cause. Regular health checks are important.
Speak to a Clinician About Testosterone and TRT
You no longer need to wait weeks for a GP appointment to discuss testosterone. Through The GP Service, you can consult with a licensed clinician online, discuss your symptoms in detail, and — where clinically appropriate — receive a referral for blood testing and TRT prescription. Everything is handled confidentially, from home, at a time that works for you.
Expert clinical advice, when you need it.
Testosterone & TRT FAQs
In men, a normal total testosterone level is generally considered to be between 10 and 35 nmol/L in the UK. However, reference ranges vary slightly between laboratories, and symptoms must always be considered alongside blood results. A single morning blood test below 8 nmol/L with typical symptoms is usually sufficient to confirm hypogonadism. Levels between 8 and 12 nmol/L are borderline and typically require a repeat test and assessment of symptoms and free testosterone before deciding on treatment.
Yes. Testosterone plays an important role in women’s health, contributing to libido, energy, mood, and bone density. Women produce testosterone in the ovaries and adrenal glands, though at much lower levels than men. Low testosterone in women can occur after surgical menopause (removal of ovaries), with natural menopause, or due to certain medications such as the combined contraceptive pill. In women, the condition is less well defined and more challenging to diagnose, but symptomatic low testosterone may be treated with low-dose testosterone cream or gel under specialist supervision.
When prescribed and monitored appropriately by a clinician, TRT is generally safe and well-tolerated. Regular monitoring of blood count (haematocrit), PSA (in men over 40), lipid profile, and testosterone levels is required. TRT is not appropriate for men who wish to maintain fertility — it suppresses sperm production. It is also used with caution in men with a history of prostate cancer, severe heart failure, or polycythaemia. The risks of untreated low testosterone — including osteoporosis, cardiovascular risk, and depression — must be weighed against the risks of treatment in each individual case.
Yes, exogenous testosterone suppresses the pituitary signals (LH and FSH) that stimulate sperm production. Men who wish to father children should not take standard TRT. Alternative treatments such as hCG injections or clomiphene citrate can raise testosterone levels while preserving or even improving sperm production. These should be discussed with a clinician or specialist before starting any hormone treatment if fertility is a concern.
Different symptoms respond to TRT at different rates. Libido and mood often improve within 3–6 weeks. Energy levels typically improve within 1–3 months. Improvements in muscle mass, body composition, and bone density develop more slowly, often over 6–12 months or longer. Erectile function may take 3–6 months to respond. Some men notice significant improvement within weeks; for others, the full benefit may take 6 months or more. Blood levels are checked at 3 months initially, then every 6–12 months once stable.
No. Testosterone is a controlled medication in the UK and is only legally available on prescription from a licensed clinician. Testosterone products sold online without a prescription are unregulated, of uncertain quality, and potentially dangerous. Anabolic steroids purchased on the black market carry significant health risks including cardiovascular toxicity, liver damage, and severe suppression of natural hormone production. If you suspect you have low testosterone, the safe and appropriate route is through a clinical consultation and blood testing.
Yes. Chronic psychological stress elevates cortisol, a hormone that directly inhibits testosterone production. Acute stress has a short-term suppressive effect, while chronic stress sustained over weeks or months can result in clinically meaningful reductions in testosterone. Sleep deprivation, which often accompanies chronic stress, independently suppresses testosterone. Addressing stress through lifestyle change, psychological support, or treatment of anxiety and depression can result in modest but meaningful improvements in testosterone levels.
Yes, there is a well-established bidirectional relationship between testosterone and mood. Low testosterone is associated with low mood, depressive symptoms, irritability, and reduced motivation. These symptoms may be misattributed to primary depression and treated with antidepressants without addressing the underlying hormonal deficit. In men with confirmed hypogonadism, TRT often produces meaningful improvements in mood alongside other symptoms. However, TRT is not a treatment for primary depression in men with normal testosterone levels.