Potentiation of morphine analgesia by caffeine

Abstract
Significant potentiation of morphine (5mg kg−1 s.c. or 1 mg kg−1 i.v.) analgesia (tail‐withdrawal reflex at 55°C) was observed in caffeine‐treated (100 mg kg−1 i.p.) rats as compared to the control group and lower doses of caffeine (2mg kg−1 i.p.) did not show this effect. Potentiated analgesia was reversed by naloxone. Pharmacokinetic or dispositional factors appear to be involved in part in this potentiation.