"Acute intoxication is characterized by euphoria and drowsiness. Mast cell effects (eg, flushing, itching) are common, particularly with morphine. GI [gastro-intestinal] effects include nausea, vomiting, decreased bowel sounds, and constipation."
Source
"Opioids," The Merck Manual for Health Care Professionals, Special Subjects: Drug Use and Dependence, Opioids (Merck & Co. Inc., last revised July 2008), last accessed Jan. 12, 2013.
http://www.merckmanuals.com/p…
