| Organic | - Klinefelter's syndrome Klinefelter's Syndrome
- Cryptorchidism Undescended Testicle, anorchia
- Cancer drugs, radiation-induced testicular injury or status post-orchiectomy
- Orchitis, testicular injury or torsion
- Impact of aging on testis
| - Hypothalamic or pituitary tumours Pituitary Tumours
- Hemochromatosis Haemochromatosis
- Infiltrating or destructive diseases of the hypothalamus or pituitary gland
- Idiopathic hypogonadotropic hypogonadism
|
| Functional | | - Hyperprolactinaemia
- Opioids, anabolic steroids Steroid Doping, glucocorticoids
- Heavy alcohol use, marijuana use*
- Systemic diseases*
- Malnutrition or overtraining syndrome
- Obesity Raising the Subject of Obesity, and Assessment of Obesity, sleep apnoea Sleep Apnoea in the Adult
- Severe disease of the liver, heart or lungs*
|