Drug interactions between prescribed and over-the-counter medication.

The use and availability of over-the-counter (OTC) medication is increasing. Although regulatory agencies take care to assure than nonprescription medications are safe and effective, these drugs still have the potential to have clinically significant interactions with prescription medicines. The major classes of OTC medication to be considered in this light include antacids, histamine H2 receptor antagonists, NSAIDs, cough and cold preparations and the antiasthma products. Healthcare providers and patients/consumers should be educated regarding possible drug interactions, patient drug regimens should be simplified where possible, and all therapeutic failures and adverse reactions should be investigated with regard to the potential contribution of OTC drug products. Regulatory agencies and pharmaceutical manufacturers should ensure that nonprescription drug labelling is complete and intelligible to meet these objectives. Consideration should be given to improving the postmarketing surveillance of OTC medications.