Category B teratogens are defined as?

• A. Positive evidence of human fetal risk
• B. Animal studies show no harm; however, there are no adequate and well-controlled studies in pregnant women
• C. Adequate studies show no risk
• D. No data available

Answer: (B)

Category B teratogens are drugs for which animal studies have shown no fetal harm, but there are no adequate and well-controlled studies in pregnant women to confirm safety. This places the drug in a middle ground: animal data look reassuring, but the human data are lacking, so the fetal risk in pregnancy is uncertain. Clinicians must weigh potential benefits against this uncertain risk when considering use during pregnancy. This stands in contrast to categories where there is proven fetal risk in humans, or where well-controlled human data show no risk, or where no data are available at all.