In this article, we review published preclinical and epidemiologic studies that 
examine progesterone's role in the central nervous system. Its effects on the 
reproductive and endocrine systems are well known, but a large and growing body 
of evidence, including a recently published pilot clinical trial, indicates that 
the hormone also exerts neuroprotective effects on the central nervous system. 
We now know that it is produced in the brain, for the brain, by neurons and 
glial cells in the central and peripheral nervous system of both male and female 
individuals. Laboratories around the world have reported that administering 
relatively large doses of progesterone during the first few hours to days after 
injury significantly limits central nervous system damage, reduces loss of 
neural tissue, and improves functional recovery. Although the research published 
to date has focused primarily on progesterone's effects on blunt traumatic brain 
injury, there is evidence that the hormone affords protection from several forms 
of acute central nervous system injury, including penetrating brain trauma, 
stroke, anoxic brain injury, and spinal cord injury. Progesterone appears to 
exert its protective effects by protecting or rebuilding the blood-brain 
barrier, decreasing development of cerebral edema, down-regulating the 
inflammatory cascade, and limiting cellular necrosis and apoptosis. All are 
plausible mechanisms of neuroprotection.