Low testosterone in men: symptoms, causes and treatment

Short answer: Low testosterone causes fatigue, loss of libido and muscle loss. Diagnosis requires two blood tests plus clinical symptoms. Treatment with testosterone replacement therapy is effective, but only in cases of confirmed hypogonadism.

Persistent fatigue, a reduced sex drive, or mood swings that make no sense – many men attribute these symptoms to stress or ageing. Yet low testosterone may be the actual cause. Testosterone is the main male sex hormone and plays a role in virtually every bodily system: from muscle mass and bone density to mood and sexual function. Fellos explains when your testosterone is too low, how this is diagnosed, and what treatment options are available.

What are the symptoms of low testosterone?

The symptoms of low testosterone are often vague and overlap with other conditions, meaning they are frequently overlooked. The most common symptom is persistent fatigue combined with a lack of energy, even after sufficient sleep. In addition, men with a deficiency often experience a reduced libido. Low libido in men is one of the most frequently reported complaints in the doctor’s surgery in cases of hypogonadism. Research shows that testosterone plays a direct role in mood, motivation and well-being, and that a deficiency leads to low mood, irritability and concentration problems.

Physically, low testosterone manifests as a loss of muscle mass and an increase in fat, particularly abdominal fat. In cases of prolonged deficiency, bone loss also occurs, which increases the risk of osteoporosis. Erectile dysfunction is also common; although erectile dysfunction caused by stress is another frequent cause, a hormonal deficiency may be the underlying factor exacerbating the situation. Because the symptoms are so diffuse, the diagnosis is often not made until years later.

What is a normal testosterone level?

In adult men, total testosterone normally ranges between 10 and 30 nmol/L, although different laboratories use slightly different reference values. A single measurement falling outside this range is insufficient in itself for a diagnosis. For example, the Endocrine Society guideline states that hypogonadism is only diagnosed when two separate blood tests fall below the reference value, combined with the presence of clinical symptoms.

The time of measurement is crucial: testosterone levels follow a circadian rhythm with a clear peak in the early morning. A measurement taken later in the day may yield a falsely low value. In addition to total testosterone, free testosterone is also relevant — this is the biologically active fraction that is not bound to SHBG or albumin. In men with high SHBG levels, total testosterone may appear normal whilst free testosterone is too low, which explains the symptoms.

What are the causes of low testosterone?

Doctors distinguish between two main forms of hypogonadism. In primary hypogonadism, the problem lies in the testicles themselves: damage caused by infection, surgery or radiotherapy, congenital conditions such as Klinefelter’s syndrome, or cryptorchidism. A Lancet review describes the pathophysiology of primary hypogonadism as a direct disruption of testosterone production in the Leydig cells.

In secondary hypogonadism, the problem lies higher up in the hormonal axis: the hypothalamus or pituitary gland sends insufficient signals to the testicles. Causes include a pituitary tumour, trauma, or chronic diseases. Obesity plays a particular role: adipose tissue converts testosterone into oestrogen via the aromatase enzyme, creating a negative feedback loop that further suppresses production. In addition to structural causes, lifestyle factors also contribute: chronic stress increases cortisol, which blocks testosterone, whilst sleep deprivation and excessive alcohol consumption disrupt the hypothalamic-pituitary axis. After the age of thirty, testosterone levels decline by an average of 1 to 2 per cent per year — a gradual process that rarely causes clinical hypogonadism on its own, but which, in combination with other factors, can certainly lead to symptoms.

How is low testosterone diagnosed?

Diagnosis begins with blood tests: total testosterone, LH, FSH and SHBG are measured. Free testosterone can be calculated based on SHBG and albumin. As described earlier, two measurements on separate days are required, preferably in the morning on an empty stomach. The American Urological Association recommends that, in the event of abnormal values, a second measurement should always be taken before the diagnosis is confirmed.

LH and FSH provide insight into the cause: high levels indicate primary hypogonadism, low levels a secondary cause. If a pituitary disorder is suspected, additional imaging investigations are carried out. The Pharmacotherapeutic Compass emphasises that a diagnosis should only be made when both low blood levels and corresponding symptoms are present — an isolated low level without symptoms does not justify treatment.

What are the treatment options for low testosterone?

In cases of confirmed hypogonadism, testosterone replacement therapy is the most effective treatment. Clinical research shows that replacement therapy improves bone density, increases muscle mass, reduces fatigue and restores libido in men with a confirmed deficiency. The most commonly used form of administration in the Netherlands is a transdermal gel, such as Androgel. The starting dose is 5 grams of gel (50 mg of testosterone) once daily, preferably applied in the morning to the shoulders or arms in a thin layer. Allow to dry for at least three to five minutes after application, then wash your hands. You should wait at least one hour before showering or swimming. Through the testosterone treatment at Fellos, you will complete an online assessment, after which a Dutch doctor will review your blood test results and draw up a treatment plan.

In addition to medication, lifestyle changes can have a significant effect in cases of mild deficiency. Weight loss reduces aromatase activity in adipose tissue, meaning less testosterone is converted into oestrogen. Getting enough sleep restores the night-time testosterone surge. Stress reduction normalises cortisol levels, thereby reducing the negative inhibition of testosterone. If you want to increase your sex drive, it is worth addressing lifestyle factors first before resorting directly to medication.

What are the risks of testosterone treatment?

Testosterone replacement therapy is safe when used correctly, but requires medical supervision and regular blood tests. The most common clinically significant side effect is polycythaemia: an increase in the number of red blood cells, which raises the risk of blood clotting. Blood tests are therefore mandatory at the start of and throughout treatment. With long-term use, the body’s own sperm production also decreases, as the body produces less LH via negative feedback.

Testosterone treatment is strictly contraindicated in men with prostate cancer or breast cancer. Transfer via the skin to a partner or children is possible as long as the gel has not completely dried, so caution is required during physical contact. Testosterone gel as a treatment option is intended exclusively for men with a diagnosed hormone deficiency, not as a performance-enhancing agent or anti-ageing therapy. If in doubt about suitability, always discuss this with a doctor.

Do you recognise these symptoms? Have your testosterone levels checked

Low testosterone is a treatable condition, provided the diagnosis is correct. Through Fellos, you’ll complete an online assessment, receive a blood test kit, and a Dutch doctor will assess whether testosterone therapy is suitable for you. Start the online assessment and find out if a hormone deficiency explains your symptoms.