Stress increases the release of cortisol, and the cortisol people cope with the stress. if stress continues for prolonged periods of time :

Stress increases the release of cortisol, and the cortisol helps people cope with the stress. If stress continues for prolonged periods of time: the increased cortisol begins to have adverse effects on bodily and mental functioning.  Increased activity in the dopamine reward systems, the same systems involved in drug addiction.