The International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) has adopted Impurities Guidelines for Residual Solvents which prescribes limits for the content of solvents which may remain in active substances, excipients and medicinal products after processing. The European Pharmacopoeia is, however, applying the same principles integrated in the guidelines to existing active substances, excipients and medicinal products whether or not they are the subject of a monograph of the Pharmacopoeia. Residual solvents were evaluated for their possible risk to human health and placed into one of three classes as follows: Class 1: Solvents to be avoided. Known human carcinogens and environmental hazards. Class 2 : Solvents to be limited .Non-genotoxic animal carcinogens or possible causative agents of other irreversible toxicity such as neurotoxicity or teratogenicity. Solvents with low toxic potential to man; no health-based exposure limit is needed. Class 3 : Solvents may be used routinely in manufacturing.