Signs of Low Testosterone in Men

Testosterone is the primary male sex hormone. It plays a critical role in energy, mood, muscle mass, bone density, fat distribution, libido, and cognitive function. According to Healthy Male — Australia's national men's health organisation funded by the Australian Government — testosterone is essential for normal male development and overall wellbeing, and deficiency can have wide-ranging physical and mental health effects.

Common signs and symptoms of low testosterone

Low testosterone (clinically known as hypogonadism or androgen deficiency) doesn't always present the same way. The Endocrine Society's clinical practice guidelines identify the following as the most commonly reported symptoms:

• Persistent fatigue — A deeper, unrelenting lack of energy that isn't explained by poor sleep or lifestyle. The Testosterone Trials (TTrials), a landmark series of seven coordinated trials funded by the US National Institutes of Health, confirmed that testosterone treatment significantly improved energy and vitality in hypogonadal men.
• Reduced libido — A noticeable drop in sexual desire. The TTrials' Sexual Function Trial, published in the New England Journal of Medicine, demonstrated that testosterone treatment improved all aspects of sexual function in men with low levels.
• Erectile difficulties — Low testosterone can contribute to difficulty achieving or maintaining erections. Healthdirect Australia (a government health information service) lists low testosterone as a recognised physical cause of erectile dysfunction.
• Mood changes — Increased irritability, low mood, and symptoms resembling depression. A meta-analysis published in JAMA Internal Medicine found that testosterone treatment produced a moderate antidepressant effect in men with hypogonadism, particularly those on lower doses.
• Loss of muscle mass — Difficulty building or maintaining muscle despite consistent training. Testosterone directly stimulates protein synthesis, and deficiency measurably reduces lean body mass.
• Increased body fat — Particularly visceral fat around the midsection, sometimes accompanied by breast tissue development (gynaecomastia). Research published in Obesity Reviews has shown a bidirectional relationship between obesity and low testosterone — each worsens the other.
• Poor sleep — Insomnia or disrupted sleep patterns. A study in the Journal of Sleep found that restricting sleep to 5 hours per night for just one week reduced daytime testosterone levels by 10–15% in young healthy men.
• Brain fog — Difficulty with concentration, memory, and mental sharpness. The TTrials' Cognitive Function Trial found modest improvements in verbal memory with testosterone treatment, though overall cognitive effects were mixed.

When should you get tested?

If you've been experiencing several of these symptoms persistently — over weeks or months rather than just a bad week — it's worth having a conversation with a GP. The only way to confirm low testosterone is through a blood test.

Testing involves a fasting morning blood draw — testosterone levels are highest in the morning and can drop by up to 25% later in the day. According to the Endocrine Society guidelines, at least two separate morning readings below the reference range are required for a diagnosis of hypogonadism. The normal reference range in Australia is typically 8–30 nmol/L for total testosterone, as outlined by Healthy Male. Your GP will also check free testosterone, SHBG, LH, FSH, and other markers to determine the cause. For details on each marker, see our blood test guide.

What causes low testosterone?

Testosterone naturally declines at roughly 1–2% per year after age 30, according to research published in the Journal of Clinical Endocrinology & Metabolism. But age isn't the only factor. Evidence reviewed by Healthy Male identifies the following:

• Obesity and excess body fat — A study in the Clinical Endocrinology journal found that weight loss through lifestyle intervention increased testosterone by an average of 2.9 nmol/L in obese men — more than what many supplements claim to achieve.
• Type 2 diabetes — Research published in JCEM found that up to 50% of men with type 2 diabetes have low testosterone.
• Chronic stress and poor sleep — Both directly suppress the hypothalamic-pituitary-gonadal axis that controls testosterone production.
• Certain medications — Particularly opioid painkillers (which can cause opioid-induced hypogonadism), corticosteroids, and some antidepressants.
• Genetic conditions — Including Klinefelter syndrome, which affects at least 1 in 600 Australian men and is significantly underdiagnosed.

Population-level testosterone may also be declining decade over decade. A Healthy Male review of the evidence suggests this is likely driven by increasing rates of obesity and chronic disease rather than environmental factors alone.

What are the treatment options?

If blood work confirms clinically low testosterone and you're experiencing symptoms, your GP may discuss testosterone replacement therapy (TRT). In Australia, TRT must be prescribed by a registered medical practitioner. Testosterone is a Schedule 4 prescription medicine regulated by the Therapeutic Goods Administration (TGA).

A comprehensive review published in peer-reviewed literature concluded that TRT in men with confirmed hypogonadism offers significant, multi-system benefits — including improvements in sexual function, body composition, bone density, insulin sensitivity, and quality of life — with a favourable safety profile under structured monitoring.

TRT requires regular blood tests to track testosterone levels, haematocrit, PSA, and liver function. For men who want to preserve fertility, alternatives such as enclomiphene may be appropriate. For cost details, see our TRT cost guide.

The bottom line

Low testosterone is a real medical condition with effective, evidence-based treatment — but it requires proper diagnosis. Get the blood work done, see a qualified GP, and make an informed decision based on your actual levels and symptoms.