Signs of Low Testosterone in Men: A Clinical Guide to Symptoms, Testing and Treatment

Low testosterone — clinically known as male hypogonadism or testosterone deficiency — is a genuine medical condition, but it is also one of the most misunderstood. Many of the symptoms that men attribute to low testosterone, such as tiredness, low mood, weight gain or a dip in drive, are non-specific: they can be caused by dozens of factors including poor sleep, stress, thyroid dysfunction, iron deficiency, depression, medication side effects and ordinary ageing.

This guide explains what testosterone deficiency actually is, which signs are worth paying attention to, how it is properly diagnosed in the UK, and what evidence-based treatment options look like — including when testosterone replacement therapy (TRT) is and is not appropriate. It is written to help you have a more informed conversation with a qualified clinician, not to replace one.

What is testosterone deficiency (male hypogonadism)?

Testosterone is the primary male sex hormone. It is produced mainly in the testes, under signalling from the pituitary gland (via luteinising hormone, LH) and hypothalamus. It plays a role in libido, erectile function, sperm production, muscle mass and strength, bone density, red blood cell production, fat distribution, mood and cognition.

Male hypogonadism is the medical term for the clinical syndrome that occurs when the body cannot produce enough testosterone, or cannot produce enough sperm, or both. Clinicians generally divide it into two categories:

• Primary hypogonadism — the problem lies in the testes themselves. LH and FSH are typically raised because the pituitary is trying to compensate. Causes include Klinefelter syndrome, undescended testes, mumps orchitis, testicular injury, chemotherapy or radiotherapy.
• Secondary (central) hypogonadism — the problem lies in the pituitary or hypothalamus, so the signal to the testes is too weak. LH and FSH are typically low or inappropriately normal. Causes include pituitary tumours or damage, high prolactin, opioid or long-term steroid use, obesity, chronic illness and Kallmann syndrome.
• Mixed / late-onset hypogonadism — a combination of both, more commonly seen with ageing and comorbidities such as type 2 diabetes and obesity.

Distinguishing between these is important, because the causes, additional tests required and treatment implications — particularly around fertility — can differ significantly.

Symptoms of low testosterone in men

Symptoms are grouped by clinical guidelines (including those from the British Society for Sexual Medicine and the Endocrine Society) into those that are more specific to testosterone deficiency and those that are less specific. The distinction matters because non-specific symptoms are common in the general population and often have other causes.

More specific signs (higher clinical relevance)

• Reduced sexual desire (libido)
• Erectile dysfunction, particularly reduced spontaneous morning erections
• Loss of body and facial hair, or reduced shaving frequency
• Very small or shrinking testes
• Infertility, or a low sperm count on semen analysis
• Reduced bone mineral density on a DEXA scan
• Hot flushes and sweats (particularly in severe deficiency)
• Breast tissue enlargement (gynaecomastia) or breast discomfort

Less specific signs (often have other causes)

• Persistent fatigue and low energy
• Low mood, irritability or reduced sense of wellbeing
• Reduced concentration or “brain fog”
• Increased body fat, particularly around the abdomen
• Reduced muscle mass and strength
• Poor sleep quality
• Mildly reduced physical performance

Because these less-specific symptoms overlap heavily with thyroid disease, iron deficiency, sleep apnoea, depression, chronic stress, poorly controlled blood sugar and simple lifestyle factors, they should not be assumed to mean low testosterone without objective testing.

What causes low testosterone?

Testosterone levels can decline for many reasons. Some are structural and permanent; others are reversible with the right changes. Common causes and contributors include:

Medical and structural causes

• Genetic conditions such as Klinefelter syndrome
• Undescended testes in childhood, testicular injury or torsion
• Mumps orchitis or other testicular infection
• Chemotherapy, radiotherapy or pelvic surgery
• Pituitary tumours (including prolactinomas) or pituitary damage
• Head injury affecting the pituitary or hypothalamus
• Haemochromatosis (iron overload)

Reversible and lifestyle-related contributors

• Obesity — one of the strongest modifiable contributors to low testosterone in adult men
• Type 2 diabetes and metabolic syndrome
• Poor or short sleep, including untreated obstructive sleep apnoea
• Chronic psychological stress
• Excessive alcohol intake
• Overtraining or severe under-eating
• Anabolic steroid use (past or current), which suppresses the body’s own production — sometimes long after stopping
• Opioid painkillers, long-term oral corticosteroids and certain other medications
• Recreational drug use, including cannabis in some men

Ageing itself is associated with a gradual decline in testosterone of roughly 1–2% per year from around the fourth decade, but a low level in an older man should still not be dismissed as “just age” if symptoms are present — comorbidities such as obesity and diabetes usually contribute more than age alone.

When should you speak to a clinician?

Rather than a symptom count, the more clinically sensible trigger for seeking advice is a persistent, unexplained change in how you feel or function — particularly if it includes one or more of the more specific signs above (reduced libido, erectile dysfunction, reduced morning erections, loss of body hair, small testes, infertility).

You should seek prompt medical advice if you experience:

• New or worsening erectile dysfunction, especially with reduced spontaneous erections
• A noticeable loss of body or facial hair, or shrinking testes
• Breast enlargement or discomfort
• Difficulty conceiving after 12 months of regular unprotected intercourse (or 6 months if your partner is over 35)
• Symptoms following a head injury, cancer treatment or long-term opioid or steroid use

For less specific symptoms such as fatigue, low mood or weight gain, a sensible first step is a broader assessment — because in many cases the answer is not low testosterone.

How low testosterone is properly diagnosed

Testosterone deficiency is diagnosed by combining a clinical picture with laboratory confirmation. UK and international guidelines are consistent on the core principles.

1. Morning blood test

Testosterone follows a strong daily (circadian) rhythm, with levels highest in the morning and lower later in the day. A blood test taken in the afternoon can look falsely low, leading to misdiagnosis. Guidelines recommend testing between 7am and 11am, and ideally while fasted.

2. Repeat testing is essential

A single low reading is not enough to diagnose testosterone deficiency. Levels can be temporarily suppressed by acute illness, poor sleep, alcohol, intense training or emotional stress. Guidelines from NICE, the Endocrine Society and the British Society for Sexual Medicine recommend confirming a low result with a second morning test, typically at least 4 weeks apart, before making a diagnosis or starting treatment.

3. Total testosterone, free testosterone and SHBG

Most testosterone in the blood is bound to a protein called sex hormone binding globulin (SHBG) and, to a lesser extent, albumin. Only a small fraction is “free” and biologically active.

• Total testosterone — the standard first-line measurement.
• SHBG — helps interpret the total. SHBG can be high (raising total testosterone artificially — common in older men, hyperthyroidism, liver disease) or low (lowering total — common in obesity, type 2 diabetes, hypothyroidism).
• Free testosterone or calculated free testosterone — particularly useful when SHBG is abnormal or when total testosterone sits in the borderline range.

4. Other tests a clinician may consider

Depending on your symptoms and initial results, an appropriate workup often includes:

• LH and FSH — to distinguish primary from secondary hypogonadism
• Prolactin — a raised level can point to a pituitary problem
• Oestradiol — particularly relevant in overweight men and before or during TRT
• Thyroid function (TSH, free T4) — because thyroid disease mimics many of the same symptoms
• Full blood count and haematocrit — baseline before TRT and monitored on treatment
• Ferritin and iron studies — iron deficiency causes fatigue; iron overload can affect the testes
• HbA1c and lipid profile — to assess metabolic health
• PSA — recommended before starting TRT in men over 40, and monitored during treatment
• Semen analysis — if fertility is a concern

Interpreting the numbers

Reference ranges vary by laboratory and by assay method, so there is no single universal cut-off. As a guide, most UK laboratories consider total testosterone below approximately 8 nmol/L (about 230 ng/dL) as consistent with hypogonadism, and levels above around 12 nmol/L (about 350 ng/dL) as generally reassuring in the absence of specific symptoms. Values in between are a “grey zone” where free testosterone, symptoms and other markers guide the decision. Interpretation should always be done by a qualified clinician using the specific reference range from your laboratory.

Treatment options for low testosterone

Treatment depends on the cause, the severity, your symptoms, your age and — importantly — whether you want children in the future.

Address reversible causes first

In many men, particularly those with borderline results, addressing modifiable factors can meaningfully improve testosterone and, more importantly, overall health:

• Weight loss in men with obesity — one of the best-evidenced non-drug interventions
• Treating obstructive sleep apnoea and improving sleep quality and duration
• Improving glycaemic control in type 2 diabetes and prediabetes
• Reducing alcohol intake
• Reviewing medications with a prescriber — particularly opioids and long-term corticosteroids
• Balancing training load and nutritional intake in athletes
• Managing chronic stress

Testosterone replacement therapy (TRT)

Where a clinical diagnosis of hypogonadism is confirmed on two morning tests and reversible causes have been addressed or excluded, testosterone replacement therapy may be appropriate. In the UK, TRT is usually prescribed as an intramuscular injection (short-acting testosterone enantate or long-acting testosterone undecanoate), a transdermal gel, or occasionally a subcutaneous injection or implant.

The aims of TRT are to restore testosterone into the normal physiological range, improve symptoms and preserve long-term health markers such as bone density. It is a long-term treatment and should always be prescribed, initiated and monitored by a qualified clinician.

Monitoring on TRT

Monitoring is not optional — it is what makes TRT safe. Guidance typically includes:

• Bloods at approximately 3, 6 and 12 months in the first year, then at least annually
• Monitoring of haematocrit (red blood cell concentration), which can rise on treatment and, if too high, increase clotting risk
• Regular PSA checks, especially in men over 40
• Blood pressure review
• Assessment of symptom response

Risks and contraindications

TRT is generally well tolerated when properly monitored, but it is not risk-free and is not appropriate for everyone. Absolute contraindications include a current or previous diagnosis of prostate cancer or male breast cancer. Caution is needed in men with severe untreated sleep apnoea, uncontrolled heart failure, a raised haematocrit, active clotting disorders or severe lower urinary tract symptoms. Potential side effects include acne, fluid retention, mood changes, breast tissue changes and, importantly, effects on fertility (see below).

TRT and fertility

This is one of the most under-discussed issues in TRT and deserves particular emphasis. Exogenous testosterone suppresses the body’s own production of LH and FSH, which in turn suppresses sperm production. TRT should be considered as effectively contraceptive while it is being used, and it can result in prolonged or, in some cases, permanent infertility even after stopping.

If you are considering having children in the future, discuss this with your clinician before starting. Alternative approaches — such as clomifene (used off-label in the UK), hCG-based protocols, or sperm banking prior to treatment — may be more appropriate for men who wish to preserve fertility.

Getting tested with Youth Revisited

If you would like to investigate your hormones with a UK-accredited laboratory and a clinical review, Youth Revisited offers home testing and specialist consultations. The most relevant starting points are:

• The Male Hormone Profile — a broad baseline covering total and free testosterone, SHBG, LH, FSH, prolactin, oestradiol, progesterone and DHEA-S.
• The TRT Eligibility Test — the specific panel used if you are exploring testosterone replacement therapy.
• The Health Optimisation Blood Test — a full-body panel including thyroid, metabolic markers, PSA, vitamins and cardiovascular risk, useful when symptoms are non-specific and other causes need excluding.

You can also take our free, confidential TRT eligibility check for an honest indication of whether TRT is likely to be appropriate for you, or book a consultation with a specialist to discuss your situation before ordering any test.

Frequently asked questions

Can low testosterone be reversed naturally?

In many men — particularly those with obesity, poorly controlled blood sugar, sleep apnoea or high alcohol intake — addressing these factors can meaningfully increase testosterone. In men with true primary hypogonadism (a problem with the testes themselves), the deficiency is usually permanent and lifestyle changes alone will not restore normal levels.

Does low testosterone always cause erectile dysfunction?

No. Erectile dysfunction has many causes, including vascular disease, diabetes, medications, psychological factors and neurological conditions. Testosterone deficiency can contribute, particularly through reduced libido, but most men with erectile dysfunction have a normal testosterone level.

What is a “normal” testosterone level for a man?

Reference ranges vary by laboratory and assay, but most UK labs use a lower limit of approximately 8–12 nmol/L. Interpretation should combine your specific lab’s reference range, your symptoms, SHBG, free testosterone and other markers — not a single number in isolation.

Should I test my testosterone at home?

Home finger-prick or venous kits from accredited UK laboratories can provide clinically valid results, provided the sample is taken correctly and at the right time (morning, fasted). Home testing is a reasonable first step, but any low or borderline result should be repeated and reviewed by a qualified clinician before any treatment decision.

Is low testosterone dangerous?

Untreated symptomatic hypogonadism is associated with reduced bone density and, over time, an increased risk of fractures. It is also associated with reduced quality of life and, in some studies, with cardiovascular and metabolic risk — although causation here is complex. The point of assessment and treatment is not to chase a number, but to protect long-term health and quality of life where a genuine deficiency exists.

Can young men have low testosterone?

Yes. Genetic conditions such as Klinefelter syndrome, undescended testes, pituitary problems, prior anabolic steroid use, opioid use and chronic illness can all cause hypogonadism in younger men. Any young man with low testosterone should have a thorough clinical assessment rather than simply starting TRT, particularly if fertility may matter in the future.

Does TRT shrink the testicles?

Because exogenous testosterone suppresses LH and FSH, the testes reduce their own hormone and sperm production and often become smaller during treatment. This is one reason fertility must be discussed before starting TRT.

Is TRT available on the NHS?

TRT is available on the NHS for men with confirmed hypogonadism, but access varies by region and many men find NHS thresholds and waiting times restrictive. Private clinics such as Youth Revisited work within the same clinical guidelines but often assess symptom burden alongside blood results and can typically initiate assessment more quickly.

How long does it take to feel better on TRT?

Different symptoms improve on different timelines. Libido and mood often improve within the first few weeks. Body composition changes and improvements in strength take several months. Bone density changes take a year or more. Individual responses vary considerably.

Medical disclaimer

This article is for general information and education. It is not medical advice and is not a substitute for consultation with a qualified healthcare professional. Do not start, stop or change any treatment on the basis of this content. If you are experiencing severe or worrying symptoms, contact your GP or, in an emergency, call 999 or attend A&E. Testosterone replacement therapy is a prescription-only medicine in the UK and must only be initiated and monitored by an appropriately qualified prescriber.

References

1. NHS. Male menopause (andropause). NHS website.
2. NICE Clinical Knowledge Summary. Hypogonadism in men.
3. Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism, 2018.
4. Hackett G, Kirby M, Edwards D, et al. British Society for Sexual Medicine Guidelines on Adult Testosterone Deficiency, With Statements for UK Practice. Journal of Sexual Medicine, 2017.
5. European Association of Urology. Guidelines on Sexual and Reproductive Health.
6. Corona G, Rastrelli G, Maggi M. Diagnosis and treatment of late-onset hypogonadism. Best Practice & Research Clinical Endocrinology & Metabolism.