FDA Pregnancy Categories and Medication Use

Historical FDA Letter Categories (Pre-2015)

Controlled studies in pregnant women demonstrated no fetal risk in any trimester, which is the safest designation, though very few drugs achieved this rating, according to the European Heart Journal and Ophthalmology 1, 2, 3, 4
Category B drugs, such as brimonidine, have either animal studies showing no fetal risk but human studies are lacking, or animal studies showed adverse effects that were not confirmed in controlled human studies, as reported by the European Heart Journal and Ophthalmology 1, 2, 3
Category C drugs, including beta-blockers, prostaglandin analogs, carbonic anhydrase inhibitors, and parasympathomimetics, have animal studies revealing adverse fetal effects and no controlled human studies exist, and should only be given if potential benefits justify potential fetal risks, according to the European Heart Journal and Ophthalmology 1, 2, 3
Category D drugs, such as valsartan, have positive evidence of human fetal risk, but benefits from use in pregnant women may be acceptable despite the risk, and should be used with caution, as stated by the European Heart Journal and American family physician 1, 2, 5, 6
Category X drugs have studies in animals or humans demonstrating fetal abnormalities, and are contraindicated in women who are or may become pregnant, according to the European Heart Journal and American family physician 1, 2, 6

The American Academy of Family Physicians recommends avoiding FDA category X medications and most category D medications unless potential maternal benefits outweigh fetal risks 6
In emergency or life-threatening maternal conditions, necessary medications should not be withheld even if pregnancy safety data are incomplete, as stated by the European Heart Journal and American family physician 1, 2, 5, 6