Typically, a man's testosterone level is considered low if it's below a level of approximately 300 ng/dL. Low testosterone can be caused by a signaling problem that occurs between the brain and the testes that causes the production of testosterone to drop below normal. Low testosterone also can occur when the body can't make normal levels of testosterone and can lead to a medical condition known as hypogonadism that has many symptoms including fatigue, decreased energy, reduced sexual desire and depressed mood.
It is estimated that low testosterone affects more than 4 to 5 million men in the U.S. Common symptoms include reduced sex drive, decreased energy, loss of body hair or reduced shaving, and depressed mood. There is no cure for hypogonadism. It is a medical condition that usually requires ongoing treatment.