Table 2: Pregnancy Risk Categories for Pharmacologic Agents.

US FDA category	Explanation
Explanation	Controlled human studies indicate no apparent risk to the fetus. The possibility of risk to the fetus is remote.
Category B	Animal studies do not indicate fetal risk. Well-controlled human studies have failed to demonstrate a risk
Category C	Animal studies show an adverse effect on the fetus but there are no controlled studies in humans. The benefits from use of such drugs may be acceptable.
Category D	Evidence of human risk, but in certain circumstances the use of such a drug may be acceptable in pregnant women despite its potential risk.
Category X	Risk of use in pregnant women clearly outweighs possible benefits.