Effects of naloxone on experimentally induced ischemic pain and on mood in human subjects.

The hypothesis that painful stimuli activate the endogenous opioid (endorphin) system in humans was tested by examining the effect of the opiate antagonist naloxone on experimentally induced ischemic pain and on subjective mood ratings. Intravenous injections of saline or naloxone hydrochloride (2 and 10 mg) were administered under double-blind conditions to 12 subjects. Naloxone did not affect the pain ratings. However, a significant dose-related effect of naloxone on tension-anxiety was found, suggesting that the endorphins. like exogenously administered opiates, may have antianxiety properties.