The calcium channel antagonist nifedipine causes confusion when used to treat opiate withdrawal in morphine-dependent patients.

Several animal studies have suggested that calcium channel antagonists may be clinically effective in the treatment of opiate withdrawal. In this study we aimed to examine whether the alpha 2-adrenoceptor agonist clonidine and the calcium channel antagonist nifedipine were equally effective in attenuating the naltrexone-precipitated opiate withdrawal syndrome. We planned to study 16 morphine-dependent in-patients in a double-blind trial. However, the study had to be abandoned after only four patients were entered into it because the first two patients treated with nifedipine became severely confused following naltrexone. The mechanism underlying the development of delirium in these two patients is uncertain, but might possibly relate to a large unopposed release of noradrenaline within the central nervous system. These findings suggest that the calcium channel antagonist nifedipine is not effective in the clinical treatment of opiate withdrawal. Whether other calcium channel antagonists also cause confusion when used in this clinical condition is uncertain at present, but in any future studies investigating their efficacy considerable care is required in their use.