Low Testosterone (Low T): Causes, Symptoms, and What to Do Next

The Short Answer

Low testosterone, sometimes called “Low T” or hypogonadism, means your body isn’t producing enough testosterone for normal function. It’s most commonly related to ageing, but can also stem from issues with the testicles themselves, the pituitary gland or hypothalamus (which signal the testes to produce testosterone), certain medications, or health conditions such as obesity and metabolic syndrome. Symptoms vary widely between individuals, and the only reliable way to confirm low testosterone is a blood test, not symptoms alone, since many overlap with other common conditions.

What Causes Low Testosterone?

Low testosterone is generally grouped into two broad categories:

Primary (Testicular) Causes

This is where the problem originates in the testicles themselves, which fail to produce enough testosterone despite receiving normal signals from the brain. Causes include:

Testicular injury or infection
Klinefelter’s syndrome (a genetic condition)
Undescended testicles
Chemotherapy or radiation treatment
Ageing-related decline in testicular function

Secondary (Pituitary/Hypothalamus) Causes

Here, the testicles function normally, but a problem elsewhere, usually the pituitary gland or hypothalamus — means they don’t receive adequate signal to produce testosterone. Causes include:

Pituitary tumours or disorders
Obesity and metabolic syndrome
Chronic illness or significant stress
Certain medications, including some antidepressants, opioid painkillers, and long-term steroid use

Age-Related Decline

The most common cause overall is simply ageing. Testosterone naturally declines gradually, often cited at around 1–2% per year after age 30–40 — though the pace and impact vary considerably between individuals. This gradual, age-related decline is sometimes referred to informally as the “male menopause,” though this is a somewhat misleading term, since it doesn’t involve the sharp hormonal drop associated with female menopause.

Common Symptoms of Low Testosterone

Symptoms vary widely, and many overlap with other common conditions — which is exactly why a blood test, not symptoms alone, is needed to confirm low testosterone. Commonly reported symptoms include:

Reduced libido and erectile difficulties
Persistent fatigue and low energy
Low mood or irritability
Reduced muscle mass and strength
Increased body fat, particularly around the abdomen
Loss of body or facial hair
Reduced bone density over time
Difficulty concentrating or “brain fog”
Hot flushes or sweating (less commonly reported)

Because these symptoms are also common in men with entirely normal testosterone levels, often linked to stress, poor sleep, or other health conditions, testing is the only way to know whether low testosterone is actually the cause.

Who Is at Higher Risk?

Certain factors increase the likelihood of low testosterone, including:

Obesity and metabolic syndrome
Type 2 diabetes
Chronic use of opioid painkillers, certain antidepressants, or long-term corticosteroids
Significant, prolonged stress or poor sleep
Underlying pituitary or testicular conditions

What to Do If You Suspect Low Testosterone

Track your symptoms. Note what you’re experiencing and how long it’s been going on, this helps a GP assess the full picture rather than a single symptom in isolation.
See your GP, or consider a private test first. Your GP can arrange NHS blood tests, though referral criteria and wait times vary — see our comparison of NHS vs. private testing. A private test can also give you a starting point to bring to a GP conversation.
Test in the morning. Testosterone follows a daily rhythm and is generally highest earlier in the day, so morning testing (ideally before 10-11am) gives a more representative reading.
Get a repeat test if the result is low or borderline. A single low reading is often confirmed with a second morning test before any treatment decision is made.
Discuss results with a qualified professional. Only a GP or specialist can properly interpret your result alongside your symptoms and medical history, and advise on appropriate next steps, including whether treatment such as TRT is suitable. See TRT Explained.

Frequently Asked Questions

What is considered low testosterone?

UK clinical guidance generally treats total testosterone below 8 nmol/L as clearly low, with 8–12 nmol/L often described as a borderline “grey zone” requiring clinical judgement alongside symptoms. See our full guide on normal testosterone levels by age.

Can low testosterone be reversed?

It depends on the underlying cause. Lifestyle-related contributors (such as obesity or poor sleep) may improve with changes in those areas, while other causes may require ongoing medical management such as TRT under specialist supervision.

Is Low T the same as the “male menopause”?

“Male menopause” is an informal term sometimes used for age-related testosterone decline, but it’s a misleading comparison, it doesn’t involve the sharp hormonal drop seen in female menopause, and not all men experience it in the same way.

Can stress cause low testosterone?

Yes, chronic stress is a recognised contributor to lower testosterone levels, generally through its effect on the hypothalamic-pituitary-gonadal axis that regulates hormone production.

Do I need to see a doctor, or can I just order a test kit myself?

ou can order a private test without seeing a GP first, but any low or borderline result should still be discussed with a GP or specialist, who can consider your full medical history and advise on next steps — including whether further tests or treatment are appropriate.