Low testosterone may be caused by a problem in the testes, reduced signalling from the hypothalamus or pituitary, or functional suppression related to obesity, illness, medicines, sleep or exposure to external androgens. Identifying the cause can completely change the treatment plan.
What testicular problems can lower testosterone?
Causes include Klinefelter syndrome and other genetic conditions, torsion or trauma, orchitis, surgery, chemotherapy, radiotherapy and other acquired testicular damage. In primary hypogonadism, LH and FSH are often raised because the brain is trying to stimulate testes that are responding inadequately.
What about hypothalamic or pituitary causes?
Pituitary tumours or lesions, raised prolactin, iron overload, trauma, systemic disease and certain medicines can reduce LH/FSH signalling. A raised prolactin, neurological symptoms or a striking hormonal pattern can justify further investigation.
Can obesity lower testosterone?
Yes. Obesity is one of the commonest associations with lower testosterone. It can lower SHBG and also suppress the hypothalamic-pituitary-testicular axis.
In some men, weight loss and treatment of associated conditions improve both testosterone and symptoms without a structural testicular problem being present. This does not mean every low result in a man with obesity is caused only by weight.
Which medicines and substances can lower it?
- Opioids: can suppress GnRH and reduce LH and testosterone.
- Glucocorticoids: can affect the hormonal axis with relevant exposure.
- Testosterone and anabolic steroids: suppress endogenous production; recovery after stopping may take months.
- Other treatments: some cancer and hormonal medicines directly affect gonadal function.
Do sleep, illness and energy intake matter?
Acute illness, insufficient sleep, obstructive sleep apnoea and severe energy deficit can all affect hormonal levels. If the result was taken during a major temporary stressor, repeating it once you are stable can help avoid misdiagnosis.
Is age itself a cause?
Testosterone tends to change with age, but ageing does not explain every low result. Obesity, comorbidity, medicines and changes in SHBG are important too. Age never removes the need for compatible symptoms and biochemical confirmation.
Source: EAU 2026.