Signs of Low Testosterone in Men: Symptoms, Causes & Next Steps

By Jordan Harvey · 23 July 2026 · Updated 23 July 2026 · 8 min read

Most men notice it as a vague sense that something is off rather than a single dramatic symptom: less energy than you used to have, a flatter mood, a body that holds more fat and less muscle than it once did. Low testosterone — the clinical term is testosterone deficiency, or hypogonadism — can produce all of these, but so can plenty of other things, from poor sleep to stress to an underactive thyroid. This guide explains the common signs of low testosterone in men, what can cause them, and — most importantly — when and how to see your GP, because the only reliable way to know is a blood test, not a symptom checklist.

What Testosterone Does

Testosterone is the main male sex hormone, made mostly in the testicles and regulated by signals from the brain (the pituitary gland and hypothalamus). It does far more than its reputation suggests. From puberty onward it drives the development of male physical features, but in adult men it also helps maintain muscle mass and strength, bone density, the making of red blood cells, body-fat distribution, mood and concentration, and sexual function. Levels naturally peak in early adulthood and drift down slowly with age — roughly 1–2% a year from around the late 30s, according to commonly cited estimates.

Because the hormone touches so many systems, a genuine shortfall tends to show up as a cluster of changes rather than one neat symptom. That is also why the signs overlap with so many other conditions, and why a checklist alone cannot tell you whether testosterone is the cause.

Common Signs of Low Testosterone

The signs below are the ones most often linked to testosterone deficiency in men. Read them as prompts to get checked, not as a self-diagnosis. Having several does not confirm anything, and having none does not rule it out.

Low energy and persistent tiredness Common but non-specific

One of the most frequently reported symptoms is fatigue that does not lift with rest — feeling drained through the day, or finding usual activities harder than they were. Because tiredness has dozens of possible causes, it is a weak signal on its own, but a common one.

Low mood, irritability and reduced motivation

Some men with low testosterone describe a flatter mood, low motivation or increased irritability. The overlap with depression is significant and runs both ways, which is one reason a GP will usually consider mental health alongside hormones rather than assuming one cause.

Reduced muscle and increased body fat

Testosterone helps maintain lean muscle, so a sustained drop can show up as a loss of strength or muscle, often alongside an increase in body fat — particularly around the midsection. This change tends to be gradual and is easily attributed to ageing or lifestyle, which it often partly is.

Poor concentration and “brain fog”

Difficulty concentrating or a sense of mental fog is reported by some men with low testosterone. Like fatigue, it is non-specific and frequently driven by poor sleep, stress or low mood rather than hormones directly.

Disturbed sleep

Poor or broken sleep is both a possible symptom of low testosterone and a possible cause of it — the relationship runs in both directions, which makes sleep an important thing for a GP to ask about. Untreated sleep apnoea (where breathing repeatedly stops during sleep) is a recognised contributor.

Reduced sexual desire and related symptoms

Reduced sexual desire is one of the more specific symptoms, and is the clinical term doctors use. Some men also notice fewer spontaneous erections or changes in sexual function. Because these symptoms can also stem from circulation, medication, stress or relationship factors, they are best discussed openly with a GP, who can look at the whole picture rather than assume a single cause.

What Can Cause Low Testosterone

Testosterone can fall for many reasons, and they often overlap. Identifying the cause is part of why proper medical assessment matters — some causes are reversible, and some point to a separate condition that needs treating in its own right.

“Hypogonadism” simply means the body is not producing enough sex hormone. It is split into primary (a problem in the testicles themselves) and secondary (a problem with the brain signals that tell the testicles to produce testosterone). Distinguishing the two needs medical tests — another reason this is a GP conversation, not a self-assessment.

When and How to See Your GP

Your GP will usually start by asking about your symptoms, sleep, weight, medications and general health, because so many of the signs have other explanations. If low testosterone is a realistic possibility, the next step is a blood test.

The blood test: what to expect

Testosterone follows a daily rhythm and is highest in the morning, so guidance from bodies such as the British Society for Sexual Medicine (BSSM) and the European Association of Urology (EAU) recommends a morning total testosterone sample, typically taken before 11am and ideally when you are not unwell. Because a single low reading can be a fluke, the same guidance recommends repeating the test to confirm, usually with additional measures such as free testosterone and the pituitary hormones (LH and FSH) to help find the cause.

If testing confirms low testosterone, your GP can investigate the cause and discuss management, which may include treating an underlying condition, addressing reversible factors such as weight or sleep, or referral to a specialist. Any decision about medical treatment is one for your doctor.

Evidence-Based Steps That May Help

If your levels come back firmly low, that is a medical matter for your GP. But for men whose results are low-normal, or who simply want to give their health the best footing, several everyday changes are consistently linked to better hormonal and overall health in the research. These are general health measures, not a substitute for diagnosis.

• Reach and hold a healthy weight. Excess body fat is one of the strongest modifiable factors associated with lower testosterone, and weight loss in men with obesity has been associated with higher measured levels in several studies.
• Sleep well. Short or fragmented sleep is associated with lower testosterone; treating sleep apnoea, where present, is part of this.
• Move regularly. Resistance training and general physical activity are associated with better hormonal and metabolic health.
• Eat a balanced diet. Including adequate protein and micronutrients; some nutrients, such as zinc, have a recognised role in normal hormone function.
• Manage stress and alcohol. Both chronic stress and heavy drinking are associated with lower levels.

For a fuller, practical walk-through of these habits, see our guide on how to look after your testosterone naturally. If you are weighing up products, our overview of natural testosterone support sets out what the evidence does and does not show, and our guide to supplements for men over 40 covers wider midlife health.

Frequently Asked Questions About Low Testosterone

The Bottom Line

The signs of low testosterone — low energy, flat mood, reduced muscle, more body fat, poor concentration, disturbed sleep and reduced sexual desire — are real, but they are also shared with many other conditions. That is exactly why a symptom list cannot diagnose you, and why the responsible next step is a conversation with your GP and, if appropriate, a morning blood test repeated to confirm.

If your levels turn out to be low, that is a medical matter for your doctor to manage. If they are low-normal, the everyday habits that help most are unglamorous but well evidenced: weight, sleep, movement, diet and limiting alcohol. A food supplement can sit alongside good nutrition, but it is not a treatment for diagnosed low testosterone, and it is no replacement for getting checked. If something feels off, get tested — it is the one step that actually gives you an answer.