What medications may cause contraceptive failure on the progestin only pill (POP)?
Information about drug interactions with POPs is less clear than that for combined oral contraceptive pills. As the progestins used in POPs are metabolized through the hepatic cytochrome p450 enzyme system, any medication causing enzyme induction may theoretically increase metabolism and reduce the contraceptive effectiveness of POPs. Medications that may reduce the contraceptive effectiveness of the POP may include: • Griseofulvin • Rifampin • Carbamazepine • Ethosuximide • Phenobarbital • Phenytoin • Primidone The POP should also be avoided in epileptics because the anti-epileptic drugs lower serum progestin levels secondary to increased protein binding reducing the POPs’ effectiveness.
