In pharmacology, hazardous drugs are drugs that are known to cause harm, which may or may not include genotoxicity (the ability to cause a change or mutation in genetic material). Genotoxicity might involve carcinogenicity, the ability to cause cancer in animal models, humans or both; teratogenicity, which is the ability to cause defects on fetal development or fetal malformation; and lastly hazardous drugs are known to have the potential to cause fertility impairment, which is a major concern for most clinicians. These drugs can be classified as antineoplastics, cytotoxic agents, biologic agents, antiviral agents and immunosuppressive agents. This is why safe handling of hazardous drugs is crucial.