The calcium channel antagonist, verapamil, potentiates the inhibitory action of morphine on intestinal and biliary motility.

The effects of morphine and verapamil have been assessed on the gastrointestinal propulsion of charcoal meal and egg yolk-induced gall bladder emptying in mice. Each drug significantly inhibited these functions. In combination, an additive effect was seen on the inhibition of gastrointestinal transit, whilst verapamil potentiated the morphine-induced inhibition of gall bladder emptying. It is concluded that calcium ion channel antagonists may potentiate the activity of opiate drugs.