Most of the drugs causes adverse effects, regardless of whether they are used according to instructions. Adverse effects can be manifested everywhere in the body, including the oral cavity. Adverse effects are a consequence of local but also systematic drug administration. It is very difficult to distinguish drug-induced lesions from other etiology lesions, as they can occur anywhere and in any form on the oral mucosa. The drug reaction may be received immediately after the drug is taken or after a few months or years. That is why detailed anamnesis is of utmost importance. The most common adverse effects present in the oral mucosa using systemic drugs include: hyposalvation, hypersalivation, burning mouth syndrome, taste alterations, mucosal pigmentation, angioedema, fixed drug eruption, lichenoid reaction, oral ulcerations, erythema multiforme, Steven Johnson syndrome, toxic epidermal necrolysis, drug-related lupus-like disorders, pemphigus like reactions, gingival hyperplasia, candidal infection, mucositis. Since older people use more medications, the possibility of adverse effects is increased. The dentist should be familiar with the adverse effects of medication, in order to properly treat these lesions. Of course, it would be the best to abolish the drug that cause problems, but this is sometimes impossible. It is therefore important to consult a doctor of general practice and try to find an alternative drug that will not cause adverse effects