Nature 205, 811 - 812 (20 February 1965); doi:10.1038/205811a0

Interaction of the Analgesic Effects of Morphine and Codeine in Rats

TORKELL JÓHANNESSON & L. A. WOODS

Department of Pharmacology, College of Medicine, State University of Iowa, Iowa City.

IN the experiments described here, the analgesic effects of 5.0 mg/kg of subcutaneous morphine and 60.0 mg/kg of subcutaneous codeine were determined individually at various intervals after the injections. Then, a dose of codeine too low to exert any analgesic effect by itself, when given simultaneously with morphine was demonstrated to increase the intensity and persistence of morphine analgesia. A similar experiment was performed with 60 mg/kg of codeine given with a close of morphine too low to show analgesia.

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