Several drugs may have a number of adverse reactions (ADRs) involving the oro-facial region. The dose of the drug and the time required for the reaction to take place are relevant parameters; nonetheless, ADRs mechanisms are not always known and ADRs are not always predictable since aspects other than drug pharmacodynamics and/or pharmacokinetics, as well as various interacting variables contribute to the final outcome. All tissues and many functions of the oral cavity can be affected. In particular, salivary function is frequently involved and hypo-salivation is the main manifestation; several mucosal lesions with different morphology (ulcerations, vesiculobullous lesions, white lesions, pigmentations, swelling) are also possible. Taste, sensation and trigeminal function alterations have been reported and the recent evidence regarding the occurrence of jawbones osteonecrosis, especially in bisphosphonates treated patients, is increasing. Clinical management may be quite difficult due to the multiplicity of involved classes of drugs and substances (dental materials, foods), the variety of affected tissues and functions, the type of produced lesions and disturbances, the complexity of related pathogenetic mechanisms (if known), the difficulties in assessing causality and managing drug withdrawal and/or dose adjustment, as well as in establishing specific treatments, if any. In this paper the most common and significant oral ADRs, their related aspects and importance (including medico-legal implications) for health care providers will be discussed.