Testosterone is essential for sexual and reproductive health, but taking testosterone as medication can suppress the hormones that drive sperm production. Low testosterone cannot be diagnosed from symptoms or one random blood test. It requires compatible symptoms, properly timed repeat measurements and assessment of the cause. Tell the clinician before treatment if you want children now or later.

What does testosterone do?

Testosterone is the main androgen hormone in men. It is produced mainly by Leydig cells in the testicles in response to luteinising hormone, known as LH, from the pituitary gland.

Testosterone contributes to:

• Puberty and development of male sexual characteristics
• Sex drive and sexual function
• Bone and muscle maintenance
• Red-blood-cell production
• Support of sperm production inside the testicles

Sperm production also depends on follicle-stimulating hormone, known as FSH, and very high local testosterone levels within the testicles. A testosterone blood result does not directly measure those local levels or provide a sperm count.

Does low testosterone cause infertility?

Low testosterone can be associated with reduced sperm production, especially when the testicles or the pituitary-hypothalamic hormone system are not functioning normally. It may also reduce libido or contribute to erection problems, making conception more difficult.

The relationship is not automatic. Some men with low blood testosterone still produce sperm, and some men with normal blood testosterone have severe male-factor infertility. A semen analysis is needed to assess sperm in the ejaculate.

Low testosterone may result from:

• Primary testicular failure, where the testicles cannot respond adequately
• Secondary or hypogonadotrophic hypogonadism, where pituitary or hypothalamic signalling is inadequate
• Genetic conditions
• Previous chemotherapy, radiotherapy, infection or testicular injury
• Certain medicines, including long-term opioid use
• Obesity, sleep disorders or systemic illness
• Anabolic-steroid or testosterone use

Identifying the cause matters because treatment that is appropriate for one form can be ineffective or harmful in another.

What are the symptoms of low testosterone?

More specific symptoms include reduced sex drive, erectile dysfunction and fewer spontaneous or morning erections. Other possible features can include reduced muscle strength, low bone density, anaemia, hot flushes, infertility and changes in body hair or testicular size.

Fatigue, low mood, irritability, poor sleep, reduced motivation and concentration problems are less specific. They can occur with depression, anxiety, stress, sleep apnoea, thyroid problems, medication effects and many other conditions.

Symptoms alone do not establish testosterone deficiency. Equally, one low laboratory result without relevant symptoms may not explain how you feel.

Can low testosterone cause depression or brain fog?

Low mood and concentration difficulties can occur in hypogonadism, but they are not specific enough to identify it as the cause. Testosterone should not be presented as a routine explanation for depression or as a reason to dismiss psychological assessment.

The statement in the older article suggesting that men may be prescribed antidepressants when their symptoms are “actually hormonal”, and that antidepressants will not necessarily help, should not be republished. A person can have both a hormonal condition and a mental health condition, and each needs proper assessment.

Do not stop antidepressants or another prescribed medicine because of an online article or a private hormone result. Speak to the prescriber. Seek urgent help if you have thoughts of harming yourself or feel unable to stay safe.

Does testosterone always decline with age?

Average testosterone levels can change with age, but the idea of a universal “male menopause” or a fixed one-to-two-percent loss every year is misleading. Changes vary between individuals and are influenced by health, weight, sleep, medication and illness.

Ageing symptoms such as fatigue, reduced exercise capacity or lower libido should not automatically be labelled testosterone deficiency. Late-onset hypogonadism requires both relevant symptoms and consistently low testosterone on appropriate testing.

How should testosterone be tested?

Guidelines recommend measuring total testosterone in the morning, when levels are usually highest, and in a fasting state. The Society for Endocrinology advises sampling before 11am, preferably after a good night’s sleep and not during an acute illness.

If the first result is low, it should be repeated on a separate morning before testosterone treatment is considered. A fixed gap of four to six weeks is not a universal requirement; the clinician should choose the timing based on the result and circumstances.

The assessment may also include:

• LH and FSH to distinguish testicular from pituitary or hypothalamic causes
• Sex hormone-binding globulin, or SHBG, and calculated free testosterone when total testosterone may be misleading
• Prolactin when secondary hypogonadism or relevant symptoms are present
• Thyroid, blood count, glucose or other tests based on symptoms
• Pituitary imaging in selected cases
• Semen analysis when fertility is a concern

Laboratory methods and reference ranges differ. Do not interpret a result using an online universal cut-off without the laboratory range, symptoms and related hormones.

Why can one testosterone result be misleading?

Testosterone can be temporarily lower because of:

• Testing later in the day
• Eating before the blood sample
• Poor sleep or night-shift work
• Acute illness
• Calorie restriction or rapid weight change
• Medication
• Differences between laboratory methods

This is why diagnosis uses repeat measurements and clinical context. Testing more frequently through commercial “optimisation” packages does not compensate for poorly timed or poorly interpreted samples.

Does TRT reduce sperm production?

Yes, it can. Testosterone replacement therapy, or TRT, raises testosterone in the bloodstream. The brain and pituitary respond by reducing LH and FSH. This lowers testosterone inside the testicles and suppresses sperm production.

The effect can range from a reduced sperm count to azoospermia, meaning no sperm seen in the ejaculate. Testicles may become smaller. Recovery after stopping varies and may take months or longer; it is not guaranteed to be complete.

The same warning applies to anabolic steroids and non-prescribed testosterone. A man may feel stronger or have a higher blood testosterone level while his sperm production is falling.

Can you take TRT while trying to conceive?

TRT is generally inappropriate when actively trying to conceive unless a specialist has designed and monitored an unusual individual plan. Tell the clinician explicitly that fertility matters before accepting a gel, injection, implant or another testosterone product.

If you already use prescribed testosterone:

• Do not stop abruptly without medical advice
• Ask for referral to endocrinology, andrology or reproductive urology
• Discuss semen analysis and reproductive hormone tests
• Ask what recovery and monitoring may involve
• Discuss fertility preservation if clinically appropriate

Some men with hypogonadotrophic hypogonadism can be treated with gonadotrophins to stimulate testicular testosterone and sperm production. The 2026 NICE fertility guideline recommends gonadotrophin therapy for this diagnosis. That is different from giving testosterone from outside the body.

Is testosterone treatment ever appropriate?

Yes. Testosterone replacement can be appropriate for men with a well-founded diagnosis of hypogonadism who are not currently seeking fertility, after benefits, risks and alternatives have been discussed.

A sound diagnosis requires:

• Relevant symptoms or signs
• Low testosterone confirmed on appropriately timed repeat testing
• Assessment of the underlying cause
• Consideration of reversible contributors
• A discussion of fertility goals
• Baseline safety checks and a monitoring plan

Treatment should not be prescribed merely to move a normal level higher, improve gym performance or treat nonspecific symptoms without a diagnosis.

What monitoring is needed with TRT?

Monitoring depends on age, medical history, treatment type and local guidance. It may include:

• Symptoms and treatment response
• Testosterone level at a time appropriate for the formulation
• Haematocrit or full blood count because testosterone can increase red blood cells
• Blood pressure and cardiovascular risk review
• Prostate assessment and PSA when appropriate
• Side effects such as acne, breast symptoms, sleep-apnoea worsening or fluid retention
• Fertility goals and testicular changes

The dose should be adjusted by the prescribing clinician. Unsupervised products may contain an inaccurate dose or expose you to avoidable risk.

Can lifestyle raise testosterone?

Improving sleep, physical activity, nutrition and weight can support health and may improve testosterone in some men, particularly when obesity or non-gonadal illness contributes. Treating sleep apnoea or reviewing a relevant medicine may also help.

Lifestyle is not a guaranteed cure for genetic, pituitary or primary testicular hypogonadism. Conversely, a low result during acute illness or major calorie restriction does not automatically mean lifelong TRT is needed.

Focus on sustainable health rather than “testosterone-boosting” foods, extreme diets or supplements. Ask for a clinical diagnosis when symptoms persist.

What happens if low testosterone and an abnormal semen analysis are found?

The combination should prompt investigation rather than immediate TRT. After two or more abnormal semen analyses, NICE says to offer a physical examination of the scrotum and testicles and consider testosterone and gonadotrophin measurements.

Depending on the pattern, further assessment can involve:

• Endocrinology or reproductive-urology referral
• Genetic testing for azoospermia or very low sperm concentration
• Examination for a varicocele or other testicular problem
• Review of anabolic steroids, testosterone, opioids and other medicines
• Imaging when pituitary or scrotal disease is suspected
• Discussion of fertility preservation or treatment

Read Male Fertility Testing Through Your GP for the wider pathway.

Questions to ask before starting testosterone

• Do my symptoms and two appropriate morning tests support a diagnosis of hypogonadism?
• Were the tests fasting and taken when I was well?
• What do LH, FSH, SHBG and prolactin suggest about the cause?
• Could sleep, weight, medication or another illness be contributing?
• How will this treatment affect sperm production?
• Do I want children now or later, and should I have a semen analysis or discuss preservation first?
• Is a fertility-preserving treatment appropriate for my diagnosis?
• What benefits should I realistically expect?
• What are the risks, monitoring schedule and stopping plan?
• Who will manage treatment over the long term?

The most important thing to remember

Testosterone is essential for sperm production inside the testicles, but testosterone medication can switch that production down. Diagnose low testosterone with symptoms, repeat correctly timed blood tests and assessment of the cause. If fertility matters, make it part of the decision before treatment starts, not after the sperm count changes.

The original Male Fertility Podcast episode with Dr Jonathan Andrews discusses testosterone, symptoms, testing, treatment and fertility. Any quotation or personal recommendation attributed to him should be checked against the recording and approved before publication.

For peer support, join The Male Fertility Hub community.

Sources

• Society for Endocrinology and Association for Laboratory Medicine: Standardising the biochemical confirmation of adult male hypogonadism
  https://www.endocrinology.org/clinical-practice/clinical-guidance/society-position-statements/
• Society for Endocrinology: Male hypogonadism and ageing
  https://www.endocrinology.org/endocrinologist/131-spring19/society-news/male-hypogonadism-and-ageing-rejuvenating-the-guidance/
• Society for Endocrinology: Male hypogonadism and testosterone replacement
  https://www.endocrinology.org/endocrinologist/143-spring-22/features/male-hypogonadism-and-testosterone-replacement/
• NHS: The “male menopause” and late-onset hypogonadism
  https://www.nhs.uk/conditions/male-menopause/
• European Association of Urology: Male hypogonadism guideline
  https://uroweb.org/guidelines/sexual-and-reproductive-health/chapter/male-hypogonadism
• NICE guideline NG257: Male-factor investigation and management
  https://www.nice.org.uk/guidance/ng257/chapter/Investigation-of-fertility-problems-and-management-strategies
  https://www.nice.org.uk/guidance/ng257/chapter/Management-of-male-factor-fertility-problems

This article provides general information and does not replace individual medical or mental-health advice. Do not start or stop testosterone, antidepressants or another prescribed medicine without speaking to the responsible clinician.