alcoholism analgesia bulimia chemotherapy congresses drugaddiction drugtolerance endorphinantagonists enkephalinase enkephalins immuneresponse immunology inhibitors metabolism naltrexone opioids pain pathophysiology pharmacology physiological physiologicalaspects physiologicaleffect physiology psychoneuroimmunology qu68d3211983 qz160e581986 receptors regulation stress stress(physiology) stress(psychology) substance-relateddisorders testing therapeuticuse therapy wm274o611988