What can cause low testosterone levels in men?

Think drugs: While it can be from a problem with your body's hormone levels and balance system (which should be checked out as some of these problems can be treated), common causes are obesity, alcohol and medications/drugs. An increasingly common cause are narcotic pain medications either as a prescription for chronic pain or from abuse. Best to be checked out to see which cause needs to be addressed.

Pituitary or testes?: In general, one can think of low testosterone as either being due to dysfunction in the pituitary ("master gland"), or the testes themselves. Checking pituitary hormones (prolactin, lh, fsh) can distinguish between these two categories, and let your doctor determine whether scanning is needed. Illness and narcotic drugs will alter pituitary function, while alcohol injures the testes to cause low t.

Also: Obesity and some chronic illnesses.