Cortisol is a steroid hormone. Cortisol is termed catabolic as it has the opposite effect to testosterone, insulin and growth hormone in that it breaks down tissue. In fact cortisol, which is released by the adrenal glands under conditions of high mental and physical stress and high temperature, is the body’s primary catabolic hormone. The three main functions of cortisol are: 1) The reduction of protein synthesis, 2) The facilitation of protein to glucose, 3) The halting of tissue growth.

The dangers of excess cortisol are: 1) Reduced growth hormone, and testosterone output, 2) Osteoporosis, 3) Reduced muscle and increased abdominal fat, 4) Impaired memory and learning, 5) Reduced glucose utilization, 6) Impaired immunity.

Source: bodybuilding.com