Nearly 50 years ago, the introduction of Enovid (norethynodrel 10 microg and mestranol 150 microg), which provided convenient and reliable contraception, revolutionized birth control. Reports of interactions between oral contraceptives (OCs) and other drugs began to trickle into the literature. At first, these drug interactions appeared to be random and unrelated. Increased understanding of P450 enzymes and phase II reactions of sulfation and glucuronidation has permitted preliminary categorization and assessment of the clinical relevance of these drug interactions.