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Health condition · Clinically reviewed

Male hypogonadism, low testosterone explained - and treated properly.

Reduced testosterone production affects libido, energy, muscle, mood and fertility. Working out whether the cause is testicular or hypothalamic-pituitary shapes the whole treatment plan.

This page focuses on the male-specific presentation. For hypogonadism in both men and women, see our general guide to hypogonadism.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against Endocrine Society and BSSM standards you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK guidance on testosterone testing, TRT, fertility-preserving options and bone health.

Key facts

Male hypogonadism at a glance.

The essentials, in plain English - what it is, how it splits into two types, and how it’s treated in the UK today.

  • What it is

    Reduced testosterone production by the testes, or reduced signalling to the testes from the brain - resulting in low testosterone and its downstream effects.

  • Primary vs secondary

    Primary (testicular) hypogonadism has high LH and FSH. Secondary (hypothalamic-pituitary) hypogonadism has low or inappropriately normal LH and FSH.

  • Broader picture

    This page focuses on the male-specific presentation. For the full condition in men and women, see our general guide to hypogonadism.

  • Diagnosis basics

    Two morning, fasting total testosterone readings, plus LH, FSH, prolactin and SHBG to work out where the fault lies.

  • First-line treatment

    Testosterone replacement therapy (gels, injections or implants) for men not wanting fertility - specialist-led with ongoing monitoring.

  • Fertility caveat

    TRT switches off natural sperm production. Men wanting children need gonadotrophin therapy instead, under specialist care.

Why this guide matters

Two different problems, one shared symptom set.

Low testosterone in men can come from the testes or from the brain's signal to the testes - and getting that distinction right changes the whole treatment plan.

  • Primary is testicular

    The testes fail despite normal signalling - LH and FSH rise. Klinefelter syndrome, torsion, chemotherapy and trauma are common causes.

  • Secondary is hypothalamic-pituitary

    The brain's signal fails - LH and FSH are low or inappropriately normal. Kallmann syndrome, pituitary tumours and opioid use are common causes.

  • Fertility changes everything

    TRT suppresses sperm production. Men wanting children need gonadotrophin therapy instead - always say so before starting treatment.

How the diagnosis is made

From a tired, low mood to a confirmed diagnosis.

The steps a UK GP or endocrinologist will normally follow, per Endocrine Society and BSSM guidance - so you know what to expect and why.

  1. 01

    Testing

    Morning, fasting total testosterone

    Blood taken before 11am, ideally fasting - testosterone follows a daily rhythm and is highest in the morning.

  2. 02

    Testing

    Repeat on a second occasion

    A single low reading is not enough - Endocrine Society and BSSM guidance both require confirmation on a separate morning sample.

  3. 03

    Testing

    LH and FSH

    These pituitary hormones distinguish primary (testicular, high LH/FSH) from secondary (hypothalamic-pituitary, low or normal LH/FSH) disease.

  4. 04

    Locating

    Prolactin, SHBG and free testosterone

    Prolactin excludes a prolactin-secreting pituitary tumour. SHBG lets free (bioavailable) testosterone be calculated when total levels are borderline.

  5. 05

    Locating

    MRI pituitary if secondary

    Low or inappropriately normal LH and FSH prompts pituitary imaging to look for a tumour or structural cause.

  6. 06

    Locating

    Karyotype if Klinefelter suspected

    Small firm testes, tall stature or infertility in a man with primary hypogonadism warrants a karyotype for Klinefelter syndrome.

  7. 07

    Planning

    Semen analysis and DEXA

    Semen analysis if fertility is a current goal; a DEXA bone density scan if hypogonadism has been present for any length of time.

Typical timeline: confirmed diagnosis and a specialist plan within a few weeks.

Symptoms

What low testosterone actually feels like.

A wide, easy-to-dismiss symptom set spanning sexual function, energy, body composition, mood and fertility - and the features that mean it’s time to escalate.

  • Low libido

    Reduced sexual desire is often the earliest and most specific symptom men notice.

  • Erectile dysfunction

    Testosterone supports but does not solely drive erections - see our dedicated guide to erectile dysfunction for the fuller picture.

  • Fatigue and low energy

    A persistent, unrefreshing tiredness that does not improve with rest or sleep.

  • Reduced muscle mass and strength

    Testosterone is anabolic - low levels reduce lean muscle and physical strength over time.

  • Increased body fat

    Particularly central, abdominal fat gain - often alongside reduced muscle, changing overall body composition.

  • Gynaecomastia

    Breast tissue enlargement from an altered testosterone-to-oestrogen ratio - see our guide to gynaecomastia.

  • Osteoporosis

    Testosterone protects bone density - long-standing hypogonadism raises fracture risk, sometimes silently.

  • Infertility

    Reduced sperm production - see our guides to low sperm count and male infertility.

  • Mood changes

    Low mood, irritability and reduced motivation are common and often under-recognised.

  • Hot flushes

    A sudden drop in testosterone, or very low levels, can trigger vasomotor symptoms similar to menopausal flushes.

  • Reduced beard and body hair

    Slower growth or thinning of facial and body hair reflects reduced androgen action.

  • Red flag - young man with small testes

    Small, firm testes with infertility or delayed puberty deserves urgent assessment for Klinefelter syndrome.

Primary vs secondary

Where the fault lies changes everything.

LH and FSH results split male hypogonadism into two distinct groups, each with its own causes and its own treatment logic.

Primary - testicular

High LH and FSH

The testes cannot respond to normal pituitary signalling, so LH and FSH rise as the brain tries harder. Also called hypergonadotropic hypogonadism.

  • • Klinefelter syndrome - the most common genetic cause
  • • Cryptorchidism (undescended testes)
  • • Testicular torsion
  • • Orchitis (testicular infection or inflammation)
  • • Chemotherapy or radiotherapy
  • • Testicular trauma

Secondary - hypothalamic-pituitary

Low or inappropriately normal LH and FSH

The testes are capable of working but never receive the right signal from the brain. Also called hypogonadotropic hypogonadism.

  • • Kallmann syndrome
  • • Pituitary tumours
  • • Hyperprolactinaemia
  • • Opioid-induced suppression
  • • Functional, obesity-related hypogonadism
  • • Ageing-related "late-onset hypogonadism"

Treatment

How male hypogonadism is treated in the UK.

Testosterone replacement for most men, fertility-preserving gonadotrophins for those wanting children, and treatment of the underlying cause wherever one is found.

  • Testosterone gel

    A daily transdermal option that mimics normal physiology closely - first choice for many men not seeking immediate fertility.

  • Testosterone injections

    Includes long-acting testosterone undecanoate (Nebido), typically every 10 to 14 weeks once stable - specialist andrology or endocrinology led.

  • Testosterone implants

    Subcutaneous pellets giving sustained release over several months - an option for men wanting less frequent dosing.

  • Fertility-preserving gonadotrophins

    hCG plus FSH stimulates the testes directly in secondary hypogonadism - used instead of TRT when fertility is wanted, specialist commissioned.

  • Treating the underlying cause

    A pituitary tumour, hyperprolactinaemia, opioid use or obesity may be driving secondary hypogonadism - treating this can restore testosterone without TRT.

  • Bone health measures

    Calcium and vitamin D, with bisphosphonates if DEXA confirms osteoporosis - alongside testosterone replacement, specialist led.

  • Ongoing TRT monitoring

    PSA, haematocrit, lipids and bone mineral density are checked regularly on treatment to catch side effects early - specialist commissioned.

  • Psychological support

    Structured support for the mood and libido impact of hypogonadism and its treatment, alongside the medical plan.

Important

Testosterone replacement therapy is not appropriate if you want to preserve or restore fertility - it suppresses natural sperm production. If fertility matters to you now or in future, say so before starting treatment, so a fertility-preserving option can be considered instead. See our guides to low sperm count and male infertility.

What this guide is based on

The sources behind every claim on this page.

UK and international specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP, endocrinologist or andrologist knows your history and can tell you which parts apply to you. If in doubt, get seen.

  • Endocrine Society. Clinical practice guideline on testosterone therapy in men with hypogonadism.

  • British Society for Sexual Medicine (BSSM). Guidelines on the assessment and management of male hypogonadism.

  • Klinefelter's Syndrome Association. Patient information and support resources.

  • European Association of Urology. Guidelines on male hypogonadism.

Red flags

When it needs urgent attention.

Most male hypogonadism is manageable through routine specialist care. These are the situations that aren’t - and where urgent input is needed.

  • Suspected pituitary tumour

    Visual field changes, severe headache or very high prolactin alongside low testosterone need urgent endocrinology assessment.

  • Testicular torsion history

    A past torsion, especially bilateral or delayed treatment, can cause permanent testicular damage - see our guide to testicular torsion.

  • Suspected Klinefelter syndrome

    Small firm testes, tall stature, learning difficulties or infertility in a young man warrants karyotype testing and specialist referral.

  • Very low testosterone with symptoms

    Marked fatigue, low mood or sexual dysfunction with a very low confirmed level should not wait for routine review.

  • Opioid-induced hypogonadism

    Long-term opioid use commonly suppresses testosterone - a medication review with the prescribing team is an important first step.

  • Unexplained anosmia with delayed puberty

    Loss of smell alongside absent or incomplete puberty suggests Kallmann syndrome and needs specialist endocrine assessment.

  • Polycythaemia on TRT

    A rising haematocrit during testosterone therapy raises clotting risk and needs dose review or treatment pause.

  • PSA rise on TRT

    Any significant PSA rise during testosterone treatment needs urological assessment before continuing.

  • Fragility fracture in a younger man

    An unexpected fracture in a man under 50 should prompt testosterone testing and a DEXA scan.

Living with it

A treatable condition, once properly identified.

Four things that make the biggest difference - confirming the diagnosis properly, deciding on fertility upfront, sticking with monitoring, and using the right support.

A quiet reminder

Low testosterone is common - and treatable.

With the right diagnosis and a specialist-led plan, most men see a real improvement in energy, mood and sexual function.

  1. 01 Confirm

    Get it properly diagnosed

    Two morning, fasting readings plus LH and FSH - not a single opportunistic blood test - before starting any treatment.

  2. 02 Fertility

    Decide on fertility first

    If you want children now or in future, say so before starting TRT - it changes which treatment is right for you.

  3. 03 Monitor

    Stick with monitoring

    Regular PSA, haematocrit, lipids and bone density checks catch problems early and keep treatment safe long-term.

  4. 04 Support

    Use the right networks

    The Klinefelter's Syndrome Association and specialist andrology clinics offer support well beyond the prescription.

Frequently asked

Everything we get asked about male hypogonadism.

Quick answers on causes, testing, testosterone replacement and fertility.

  • What is male hypogonadism?

    Male hypogonadism is reduced testosterone production, either because the testes themselves fail (primary, with raised LH and FSH) or because the brain's signal to the testes fails (secondary, with low or inappropriately normal LH and FSH). It causes low libido, erectile dysfunction, fatigue, reduced muscle mass, increased body fat, mood changes and, over time, bone loss and infertility. This page focuses on the male-specific presentation - our general hypogonadism guide covers the condition in both men and women.

  • What causes primary hypogonadism?

    The testes fail to produce enough testosterone despite adequate pituitary signalling. Common causes include Klinefelter syndrome, undescended testes (cryptorchidism), testicular torsion, orchitis (testicular infection or inflammation), chemotherapy or radiotherapy, and testicular trauma.

  • What causes secondary hypogonadism?

    The hypothalamus or pituitary gland fails to signal the testes properly. Causes include Kallmann syndrome, pituitary tumours, hyperprolactinaemia, opioid medication, functional hypogonadism related to obesity, and age-related decline sometimes called late-onset hypogonadism.

  • How is male hypogonadism diagnosed?

    Diagnosis follows Endocrine Society and BSSM guidance - a morning, fasting total testosterone repeated on two occasions, plus LH and FSH to establish whether the problem is primary or secondary. Prolactin and SHBG are checked, with free testosterone calculated when levels are borderline. An MRI of the pituitary is arranged if secondary hypogonadism is suspected, and a karyotype if Klinefelter syndrome is a possibility.

  • Can I have testosterone replacement therapy if I want children?

    No - testosterone replacement therapy switches off the body's own signal to produce sperm, so it is not suitable if you want to conceive. Men with secondary hypogonadism who want fertility are instead offered gonadotrophin therapy (hCG plus FSH), which stimulates the testes directly and can restore sperm production, under specialist care.

  • What monitoring does testosterone replacement therapy need?

    Ongoing specialist-led monitoring includes PSA and prostate checks, haematocrit (to watch for polycythaemia), lipids and bone mineral density. These checks continue for as long as treatment does, to keep it safe and catch any side effects early.

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