Table 3.

FDA drug classification during pregnancy.²⁷

Risk	Evidence
Risk A	There is no evidence of risk in pregnant women.
	Well-controlled studies have showed no problems in the first trimester of pregnancy and there is no evidence of problems in the second and third trimesters.
Risk B	There are no adequate studies in pregnant women.
	Animal experiments have detected no risks.
Risk C	There are no adequate studies in pregnant women.
	There were some side effects on the fetus in animal experiments, but the product benefit may justify the potential risk during pregnancy.
Risk D	There is evidence of risk in human fetuses.
	Only to be used if the benefit outweighs the potential risk: life-threatening situations, or in cases of severe diseases for which safer drugs cannot be used, or if these drugs are ineffective.
Risk X	Studies have disclosed abnormalities in the fetus or evidence of risk to the fetus.
	The risks during pregnancy outweigh the potential benefits. Should not be used during pregnancy under any circumstances.

FDA, United States Food and Drug Administration.