Following the widespread occurrence of birth defects from the use of thalidomide to treat nausea during pregnancy in the 1960s and 1970s, the Food and Drug Administration (FDA) became particularly vigilant about the use of therapeutic agents during pregnancy and in women of childbearing potential. The FDA developed a list that categorizes an agent according to the known (and potential unknown) risks to a fetus. The drug thalidomide falls into Category X: agents that have demonstrated clear risk of fetal abnormalities and whose risks outweigh the benefits of use during pregnancy.
Another Category X drug is isotretinoin, commonly known by its trade name Accutane. Isotretinoin is an oral medication prescribed for severe recalcitrant, nodular acne in patients who are unresponsive to conventional therapy. Isotretinoin has been available since 1982, and it remains the only effective treatment for this condition.