FDA Ratings for Medications Taken During Pregnancy (Est. 1979) Category A: Adequate and well-controlled studies have failed to demonstrate a risk to the fetus in the first trimester of pregnancy (and there is no evidence of risk in later trimesters). Category B: Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women. Category C: Animal reproduction studies have shown adverse effects on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks. Category D: Positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but the benefits from the use of the drug in pregnant women may be acceptable despite its potential risks. Category X: Studies in animals or humans have demonstrated fetal abnormalities or if there is positive evidence of fetal risk based on adverse reaction reports from investigational or marketing experience and the risk of the use of the drug in a pregnant woman clearly outweighs any possible benefit. Note that a change to the rating of medication safety was proposed by the FDA in 2011, but has not been implemented as of the publication of this version of SFL. This rating system will eliminate the A,B,C system. Most medications used in pregnancy will still be safe by the new rating system. References FDA Drug Category Ratings. American Pregnancy Association. June 2006. www.americanpregnancy.org/pregnancyhealth/fdadrugratings.html Briggs GC, Freeman RK, Yaffe SJ. Drugs in Pregnancy and Lactation, Ninth Edition. Lippincott Williams and Wilkins, Philadelphia, PA 2011.