Cortisol is a hormone in the body that reacts to stress. Normally, cortisol levels increase during stressful times and decrease when stress is not present.
During depression, cortisol levels may remain high even during times of relaxation. The corresponding low levels of serotonin and dopamine have been shown to play a part in depression. Thus raising the level of one or both of these neurotransmitters may alleviate depression. Reducing the level of cortisol has been found to increase the levels of serotonin and dopamine.
High cortisol levels are also associated with a large number of other conditions.
Heinz, A. et al. Relationship between cortisol and serotonin metabolites and transporters in alcoholism [correction of alcolholism]. Pharmacopsychiatry. 2002 Jul;35(4):127-34. 14 Jan 2010.
Field, T. et al. Cortisol decreases and serotonin and dopamine increase following massage therapy. International Journal of Neuroscience. 2005 Oct;115(10):1397-413. 14 Jan 2010.