With the exception of prenatal vitamins and possibly iron supplementation, all medications should be used with caution during pregnancy. Although clinical experience with many medications in pregnancy is quite extensive and the safety and efficacy are reasonably established, pregnancy represents a unique challenge in medication assessment. It would not be ethical, under most circumstances, to randomize pregnant patients to receive increasing doses of medications to assess safety and efficacy of a medication known to produce or suspected of producing harm in pregnancy. This limits the degree to which safety can be categorically stated for the use of any medication in pregnancy. Many medications once thought to be safe in pregnancy have subsequently been shown to be harmful. Other medications originally thought to be harmful have been shown to have beneficial effects when used for specific medically indicated purposes.