Every drug can produce untoward consequences, even when used according to standard or recommended methods of administration. Adverse drug reactions can involve every organ and system of the body and are frequently mistaken for signs of underlying disease. Similarly, the mouth and associated structures can be affected by many drugs or chemicals. Good oral health, including salivary function, is very important in maintaining whole body health. Regarding different parts of the oral system, these reactions can be categorized to oral mucosa and tongue, periodontal tissues, dental structures, salivary glands, cleft lip and palate, muscular and neurological disorders, taste disturbances, drug-induced oral infection, and facial edema. In this article, the drugs that may cause adverse effects in the mouth and related structures are reviewed. The knowledge about drug-induced oral adverse effects helps health professionals to better diagnose oral disease, administer drugs, improve patient compliance during drug therapy, and may influence a more rational use of drugs.