COMPARATIVE EFFECTS OF CODEINE AND MORPHINE IN MAN

¹ National Institute of Mental Health, Addiction Research Center, Lexington, Kentucky

This research sought to collate the effects of graded parenteral doses of codeine and morphine in 20 human male postaddicts. A six-point, double-blind, cross-over bioassay was used to contrast these drugs. Single intramuscular doses of codeine phosphate (90, 180 and 360 mg/70 kg) and morphine sulfate (7.5, 15 and 30 mg/70 kg) were compared in their production of miosis, drug identifications, opiate signs, opiate symptoms, liking (observers) and liking (subjects). Using these parameters, valid potency estimates were obtained which indicate that morphine is 7 to 14 times more potent than codeine. No significant decrement of effect in the doseresponse curve is demonstrated for either drug over these dose ranges for any of the parameters studied. Within these dose ranges, codeine and morphine produce notably similar patterns of identification, opiate signs and opiate symptoms. Codeine and morphine have a similar time action course for all variables except miosis, where codeine shows a more rapid onset and shorter duration of effect. Relative potencies calculated on the basis of total or peak data do not seriously differ in this investigation.

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