Medically Reviewed
TRT for Men:
Low Testosterone — Symptoms, Causes & Treatment
A complete guide to Testosterone Replacement Therapy — what it is, how it works, the different types available, and how to get started with a licensed UK clinician online today.
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Overview
What Is TRT and How Does It Work?
Testosterone Replacement Therapy (TRT) is a medical treatment that restores testosterone levels in men whose bodies produce insufficient amounts of the hormone. It is prescribed for a condition known clinically as hypogonadism — commonly referred to as low testosterone or testosterone deficiency syndrome (TDS).
Testosterone is the primary male sex hormone. It plays a central role in regulating libido, erectile function, muscle mass, bone density, red blood cell production, mood, energy, and cognitive function. Testosterone levels naturally decline by around 1–2% per year after the age of 30, but in some men this decline is more pronounced, or occurs at an earlier age, resulting in symptoms that significantly affect quality of life.
TRT works by supplementing the body's own testosterone production using an external source — delivered via gel, injection, patch, or other methods. This raises circulating testosterone back to a healthy physiological range, directly addressing the hormonal deficiency that causes symptoms.
TRT is a regulated prescription treatment in the UK. Diagnosis requires both a clinical assessment of symptoms and blood testing to confirm low testosterone levels. Treatment is then tailored to the individual and requires ongoing monitoring to ensure levels remain optimal and side effects are managed.
TRT requires a clinician-led assessment and a prescription. A licensed clinician can review your symptoms, arrange or review blood results, and prescribe the most appropriate treatment through a convenient online consultation.
Causes
What Causes Low Testosterone?
Low testosterone can result from problems with the testes themselves (primary hypogonadism), or from dysfunction in the brain signals that control testosterone production (secondary hypogonadism). In many men, particularly older men, the cause is a combination of age-related decline and lifestyle or health factors.
Age-Related Decline
Testosterone naturally declines by 1–2% per year after 30. By their 50s and 60s, many men have significantly lower levels than in younger years — sometimes referred to as andropause or "male menopause".
Primary Hypogonadism
The testes fail to produce adequate testosterone despite normal hormonal signals from the brain. Causes include Klinefelter syndrome, undescended testes, orchitis, testicular injury, or cancer treatment.
Secondary Hypogonadism
The pituitary gland or hypothalamus fails to send the correct signals to stimulate testosterone production. Causes include pituitary tumours (prolactinoma), head injury, or certain medications.
Obesity & Metabolic Syndrome
Excess body fat — particularly abdominal fat — converts testosterone to oestrogen and suppresses production. Metabolic syndrome, type 2 diabetes, and insulin resistance are strongly associated with low testosterone.
Chronic Stress
Elevated cortisol from prolonged stress suppresses testosterone production. Overtraining, sleep deprivation, and burnout can all contribute to functional hypogonadism.
Medications & Treatment
Opioid pain medications, steroids, antidepressants, antipsychotics, and treatments for prostate cancer can significantly suppress testosterone levels.
Key Risk Factors
Age over 40
Obesity / high BMI
Type 2 diabetes
Chronic stress or burnout
Sleep apnoea
Excessive alcohol use
Opioid or steroid use
Chemotherapy or radiotherapy
Klinefelter syndrome
Klinefelter syndrome
Pituitary disorders
Testicular injury or surgery
HIV / AIDS
Symptoms
What Are the Symptoms of Low Testosterone?
Symptoms of low testosterone are wide-ranging and often develop gradually, making them easy to attribute to stress, ageing, or lifestyle. Many men live with undiagnosed testosterone deficiency for years. If several of the following symptoms apply to you, a clinician-led assessment is worthwhile.
Physical Symptoms
- Persistent fatigue and low energy — not relieved by rest
- Reduced muscle mass and strength despite exercise
- Increased body fat, particularly around the abdomen
- Erectile dysfunction or difficulty maintaining erections
- Reduced libido and sex drive
- Decreased semen volume
- Loss of body and facial hair
- Enlarged or tender breast tissue (gynaecomastia)
- Reduced bone density (increased fracture risk)
- Hot flushes or night sweats
- Anaemia (low red blood cell count)
Psychological Symptoms
- Low mood, depression, or persistent flatness
- Irritability, mood swings, or short temper
- Anxiety
- Brain fog — difficulty concentrating or thinking clearly
- Poor memory
- Loss of motivation and drive
- Reduced confidence and self-esteem
- Social withdrawal
- Poor sleep quality or insomnia
Low Testosterone Is Frequently Missed
Many of the symptoms of testosterone deficiency — fatigue, low mood, brain fog, low libido — are non-specific and often attributed to stress, ageing, or depression. It is estimated that up to 40% of men over 45 have low testosterone, yet the vast majority are never tested or treated. A simple blood test can confirm or rule out testosterone deficiency.
Diagnosis
How Is Low Testosterone Diagnosed?
Diagnosis of testosterone deficiency requires both a clinical assessment of symptoms and laboratory confirmation of low testosterone levels. A single low reading is not usually sufficient — testing should be repeated on at least two separate occasions, ideally in the morning when testosterone is at its peak.
Test
What It Measures
Notes
Total testosterone
Overall circulating testosterone level
Primary diagnostic test; below 8–12 nmol/L is generally considered deficient depending on symptoms
Oestrogen-only HRT
Testosterone not bound to proteins; the biologically active fraction
Useful when total testosterone is borderline; can be low even if total testosterone appears normal
SHBG (sex hormone binding globulin)
Protein that binds testosterone, reducing its availability
High SHBG reduces free testosterone; important for interpreting total testosterone results
LH & FSH
Pituitary hormones that stimulate testosterone production
Helps distinguish primary from secondary hypogonadism
Prolactin
Hormone produced by the pituitary
Elevated prolactin suppresses testosterone; can indicate a pituitary tumour
Full blood count
Red blood cells, haematocrit, haemoglobin
Baseline before starting TRT; testosterone stimulates red blood cell production
PSA (prostate specific antigen)
Prostate health marker
Required before starting TRT in men over 40; monitored during treatment
Blood Tests Should Be Done in the Morning
Testosterone levels follow a diurnal rhythm, peaking in the early morning and declining through the day. For accurate results, blood samples should ideally be taken between 7am and 10am, fasting if possible. Two separate tests on different days are recommended before a diagnosis is confirmed.
Types of TRT
What Types of TRT Are Available?
TRT is available in several formulations, each with different dosing schedules, absorption profiles, and practical considerations. The best choice depends on your preferences, lifestyle, and clinical factors.
Method
Examples
Frequency
Notes
Gel
Testogel, Tostran, Androgel
Daily application to skin
Most commonly prescribed in the UK; provides stable levels; must be careful of transfer to partners or children
Injection
Sustanon 250, Nebido, Testosterone enanthate
Every 1–12 weeks depending on preparation
Nebido lasts up to 12 weeks; Sustanon every 2–3 weeks; levels can fluctuate more than with gel
Patch
Testopatch
Daily
Applied to skin; provides steady levels; skin reactions can occur
Buccal tablet
Striant
Twice daily
Applied to the gum; absorbed directly into bloodstream; bypasses liver
Nasal gel
Natesto
Three times daily
Less common; does not suppress fertility as much as other methods
Implant (pellet)
Testosterone implant
Every 3–6 months
Surgically inserted under the skin; specialist procedure; provides very stable levels
Testosterone Gel Is the Most Common Starting Point
Transdermal testosterone gel is the most widely prescribed form of TRT in the UK due to its ease of use, dose flexibility, and stable hormone levels. It is applied to the skin of the shoulders, upper arms, or inner thighs each morning. The dose can be adjusted easily, which is particularly useful in the early stages of treatment when finding the optimal level.
Benefits of HRT
What Are the Benefits of HRT?
For men with confirmed testosterone deficiency, TRT can produce significant and wide-ranging improvements across physical, psychological, and sexual health. Benefits typically accumulate over several months as levels stabilise.
Restored Energy & Vitality
Most men report a marked improvement in energy levels, motivation, and general sense of wellbeing — often within the first few weeks of starting treatment.
Improved Mood & Cognition
TRT frequently lifts low mood, reduces anxiety and irritability, and improves focus, concentration, and mental clarity — symptoms often misdiagnosed as depression.
Restored Libido & Sexual Function
Testosterone is essential for sex drive and erectile function. TRT significantly improves libido and, in many men, contributes to improved erectile function alongside or without ED medication.
Increased Muscle Mass & Strength
Testosterone stimulates muscle protein synthesis. With appropriate exercise, men on TRT typically see meaningful improvements in muscle mass and strength over 3–6 months.
Improved Bone Density
Testosterone is essential for maintaining bone mineral density. TRT reduces the risk of osteoporosis and fragility fractures in men with confirmed deficiency.
Better Sleep
Many men with low testosterone report significantly improved sleep quality on TRT, which in turn amplifies the benefits to mood, cognition, and energy.
Timeline of Benefits
Timeframe
Improvements Typically Seen
3–6 weeks
Improved energy, mood, and sense of wellbeing; reduced fatigue; initial libido improvement
6–12 weeks
Improved sexual function; improved sleep; better concentration; beginning of body composition changes
3–6 months
Increased muscle mass and strength; reduction in body fat; improved bone markers; more stable mood
6–12 months
Full body composition changes; improved bone density; maximum benefit to sexual function and mood
Risks & Considerations
What Are the Risks of TRT?
TRT is safe and well-tolerated when properly prescribed and monitored. Understanding the potential risks allows you and your clinician to manage treatment proactively.
Common & Manageable Side Effects
- Skin reactions at application site (gel or patch)
- Acne or oily skin — often mild and transient
- Elevated red blood cell count (polycythaemia) — monitored with blood tests
- Testicular shrinkage — due to suppression of natural production
- Reduced sperm production and fertility
- Fluid retention, particularly at the start of treatment
- Breast tenderness or mild gynaecomastia
- Mood changes in the early weeks of treatment
Risks to Discuss With Your Clinician
- Polycythaemia: elevated haematocrit can increase clot risk — managed with dose adjustment or venesection
- Cardiovascular effects: current evidence is mixed; recent large trials suggest TRT does not increase cardiovascular risk in most men
- Prostate: TRT does not cause prostate cancer, but should not be used in men with active prostate cancer; PSA monitored regularly
- Sleep apnoea: testosterone can worsen existing sleep apnoea
- Skin transfer: gel can be transferred to partners or children through skin contact if not careful
TRT Suppresses Natural Testosterone Production
TRT signals the brain to reduce or stop its own testosterone production. This means testicular size and sperm production may decrease during treatment. Men who wish to preserve fertility should discuss alternatives such as HCG (human chorionic gonadotropin) therapy or clomiphene citrate with their clinician before starting TRT.
TRT Is Not Suitable for Everyone
TRT is contraindicated in men with active or suspected prostate cancer, breast cancer, severe untreated sleep apnoea, or a very high haematocrit (red blood cell concentration). Men wishing to father children in the near future should discuss the fertility implications before starting treatment.
Ongoing Monitoring
What Monitoring Is Required on TRT?
Safe and effective TRT requires regular blood testing and clinical review to ensure testosterone levels remain in the optimal range, side effects are managed, and any emerging risks are identified early. Monitoring is not optional — it is an essential part of responsible TRT prescribing.
Test
Frequency
Why It Matters
Total & free testosterone
3 months after starting, then every 6–12 months
Confirms levels are in the therapeutic range; guides dose adjustments
Full blood count (haematocrit)
Every 3–6 months initially, then annually
Detects polycythaemia; dose may need reducing if haematocrit rises above 52–54%
PSA (prostate specific antigen)
At 3 months, then annually (men over 40)
Screens for prostate changes; significant rise warrants urological referral
Lipids & metabolic panel
Annually
Monitors cardiovascular risk markers
LH & FSH
If fertility is a concern
Confirms degree of suppression of natural production
Clinical review
3 months initially, then every 6–12 months
Assessment of symptoms, side effects, and treatment response
TRT & Lifestyle
TRT Is Not a Substitute for a Healthy Lifestyle
TRT works most effectively alongside — not instead of — good lifestyle habits. Men who optimise sleep, nutrition, exercise, and stress management alongside TRT typically see the greatest improvements and may require lower doses to achieve therapeutic effect.
Resistance Training
Strength training amplifies TRT's anabolic effects on muscle and bone. Aim for at least 3 sessions per week including compound movements.
Sleep Quality
Most testosterone is produced during deep sleep. Optimising sleep hygiene and addressing sleep apnoea significantly supports testosterone levels and TRT outcomes.
Nutrition
Adequate dietary fat is essential for testosterone synthesis. Caloric restriction, especially combined with low fat intake, can suppress production and blunt TRT response.
Weight Management
Losing excess body fat — particularly visceral fat — raises testosterone naturally and improves TRT efficacy. Even modest weight loss can meaningfully shift hormone levels.
Stress Management
Chronic elevated cortisol directly suppresses testosterone. Mindfulness, adequate rest, and avoiding overtraining help protect hormone levels throughout treatment.
Limit Alcohol
Alcohol suppresses testosterone production and impairs liver function, which metabolises sex hormones. Reducing alcohol intake supports better treatment outcomes.
Common TRT Medications
TRT Medications Available Through The GP Service
Our clinicians can prescribe a full range of licensed TRT products. The most appropriate choice will depend on your symptoms, preferences, lifestyle, and blood results.
Medication
Type
Route & Frequency
Testogel 50mg
Testosterone gel (1%)
Applied to shoulders / upper arms daily
Tostran 2%
Testosterone gel (2%)
Applied to abdomen or inner thighs daily; smaller volume
Androgel 16.2mg/actuation
Testosterone gel (1.62%)
Applied to shoulders or upper arms daily
Sustanon 250
Testosterone injection (mixed esters)
Intramuscular injection every 2–3 weeks
Nebido (testosterone undecanoate)
Testosterone injection (long-acting)
Intramuscular injection every 10–14 weeks
Testosterone enanthate
Testosterone injection
Intramuscular injection every 1–2 weeks
Testopatch
Testosterone transdermal patch
Applied to skin; changed daily
When to Seek Help
When Should You See a Clinician About Low Testosterone?
Seek Urgent Medical Attention If:
You experience chest pain, shortness of breath, or leg swelling whilst on TRT (possible blood clot) · You notice a sudden significant change in mood, confusion, or severe headache · You develop painful, persistent erections lasting more than four hours (priapism — rare but a medical emergency).
See a Clinician Soon If:
You have several symptoms of testosterone deficiency that are affecting your daily life, relationships, or work · You are experiencing low mood, fatigue, or low libido that isn't responding to lifestyle changes · You are already on TRT and feel your dose needs reviewing, or you are experiencing side effects · You are concerned about fertility whilst on TRT · You have been told you have low testosterone but have not yet started treatment.
Men Deserve the Same Quality of Hormonal Care
Testosterone deficiency is a legitimate medical condition with effective treatment. Yet many men are dismissed, told their symptoms are "just ageing," or left without a blood test. If you recognise the symptoms of low testosterone, you are entitled to a thorough clinical assessment. Our clinicians take men's hormonal health seriously.
Getting Treatment
How Can The GP Service Help?
Our licensed UK clinicians are experienced in menopause care and can assess your symptoms, discuss all available HRT options, review your medical history, and prescribe the most appropriate treatment — all through a convenient online consultation.
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Frequently Asked Questions
If you have questions about The GP Service, check below. Still need help? Contact our friendly patient care team.
Is TRT safe?
For men with clinically confirmed testosterone deficiency, TRT is considered safe when prescribed and monitored appropriately. Concerns about cardiovascular risk, historically associated with older studies, have not been supported by more recent large-scale trials — including the TRAVERSE trial, which found no increased risk of major cardiovascular events in men on TRT versus placebo. As with any prescription medication, TRT has potential side effects that require monitoring, and it is not appropriate for all men. Your clinician will conduct a thorough assessment before prescribing.
Will TRT affect my fertility?
Yes — TRT suppresses the hormonal signals (LH and FSH) from the brain that stimulate sperm production, which typically results in significantly reduced sperm count and potentially infertility during treatment. This effect is usually reversible when TRT is stopped, but recovery can take months and is not guaranteed. Men who wish to father children should discuss fertility preservation options — such as sperm banking before starting, or using HCG alongside TRT to maintain sperm production — with their clinician before beginning treatment.
How long do I need to take TRT?
TRT is usually a long-term or lifelong treatment for men with primary hypogonadism, as the underlying cause of low testosterone does not resolve. For men with secondary hypogonadism related to lifestyle factors — such as obesity or chronic stress — addressing the underlying cause may allow testosterone levels to recover sufficiently to discontinue TRT. Your clinician will reassess the need for ongoing treatment at each review. Stopping TRT abruptly is not recommended; it should be tapered gradually under medical guidance.
Does TRT cause prostate cancer?
Current evidence does not support a causal link between TRT and prostate cancer. The long-held "androgen hypothesis" — that higher testosterone drives prostate cancer — has not been confirmed in modern prospective studies. TRT is, however, contraindicated in men with known or suspected active prostate cancer, as testosterone can stimulate growth of existing cancer cells. PSA levels are monitored regularly in men on TRT, and any significant rise warrants urological assessment.
What is the difference between TRT and anabolic steroids?
TRT replaces testosterone to physiologically normal levels in men with confirmed deficiency — the aim is to restore levels to what a healthy man would naturally have. Anabolic steroid use involves taking testosterone or testosterone-like compounds at supraphysiological doses — far above normal ranges — primarily for performance enhancement or muscle building. This is not a medical treatment, carries significant health risks, and is illegal without a prescription. TRT prescribed by a licensed clinician uses licensed medications at therapeutic doses with regular monitoring.
Can I switch from one form of TRT to another?
Yes. If one formulation is not working well for you — whether due to skin reactions, inconvenient dosing schedules, or sub-optimal absorption — your clinician can switch you to a different delivery method. Many men try gel initially and switch to injections for convenience, or vice versa. Any change in formulation requires a period of dose optimisation and re-monitoring of blood levels.
What happens if I stop TRT?
When TRT is stopped, testosterone levels fall — usually returning to pre-treatment deficient levels, since the underlying cause has not resolved. Symptoms of low testosterone typically return within weeks to months. Natural testosterone production may also take some time to recover, as the pituitary gland has to "restart" after being suppressed. Stopping TRT should ideally be done gradually under medical supervision, not abruptly. Your clinician can support you through this if needed.
My GP said my testosterone is "normal" but I still have symptoms — what should I do?
NHS reference ranges for testosterone are broad, and a result within the normal range does not necessarily mean your level is optimal for you as an individual. Some men experience significant symptoms at levels that fall within the lower portion of the normal range — particularly if their free testosterone or SHBG levels are not factored in. It is also worth ensuring the test was taken in the morning and repeated on a second occasion. A clinician experienced in men's hormonal health can review your full picture — symptoms, blood results, and context — rather than treating the number in isolation.
Medical Disclaimer: The information on this page is provided for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare professional with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay seeking it because of something you have read on this page. If you think you may have a medical emergency, call 999 or your local emergency services immediately.