He authored 13 editions of the Catalog of Teratogenic Agents, a comprehensive compilation of chemical and environmental agents that can cause birth defects.

At issue are so-called "teratogenic" medications, used for conditions ranging from acne to anxiety, that boost the risk of birth defects when taken during pregnancy.

This is resulting in more children being born with phocomelia, or absent limbs, as thalidomide is teratogenic.