category X drug

A drug with a very high teratogenic risk to a fetus, based on controlled animal studies, which is contraindicated for use during pregnancy
Examples Accutane, thalidomide, vitamin A congeners, Xanax

category X drug

Pharmacology A therapeutic with known teratogenicity which is contraindicated for use during pregnancy–eg, vitamin A congeners–for severe acne–which cause a characteristic syndrome in neonates. See Vitamin A embryopathy.