Drug classification for use of drugs during pregnancy
| Class A | Controlled studies show no risk. Adequate well-controlled studies in pregnant women have failed to demonstrate risk to the foetus |
| Class B | No evidence of risk in humans. Either animal findings show risk, but human findings do not or, if no adequate human studies have been done, animal findings are negative |
| Class C | Risk cannot be ruled out. Human studies are lacking, and animal studies are either positive for foetal risk or lacking as well. However, potential benefits may justify the potential risk |
| Class D | Positive evidence of risk. Investigational or post-marketing data show risk to the foetus. Nevertheless, potential benefits may outweigh the potential risk |
| Class X | Contraindicated in pregnancy. Studies in animals or human, or investigational or |
(FDA Classification of Drugs for Teratogenic Risk. Teratology society public affairs committee. Teratology 1994: 49:446-447).