The FDA has released draft guidance on “Genotoxic and Carcinogenic Impurities in Drug Substances and Products: Recommended Approaches.” The document reflects the agency's views on genotoxic and carcinogenic impurities in drug substances and drug products, including biologic products regulated by the Center for Drug Evaluation and Research. It also provides recommendations on how to evaluate the safety of these impurities during clinical development and for marketing applications, including additional testing and exposure threshold recommendations when genotoxic or carcinogenic impurities are present. The draft guidance addresses synthetic impurities and degradants in drug substances, but not the genotoxicity or carcinogenicity of actual drug substances or intended drug product ingredients. This draft guidance also applies to known starting materials or anticipated reaction products. The FDA will accept comments on the guidance through February 17, 2009.