Side effects of medications are harmful and unwanted reactions to the medicine applied in the correct indication and the usual dose. Pharmacovigilance is a set of measures to gather information about the harmful and undesirable effects of drugs to prevent side effects and enhance the safety of their use. Side effects are classified into two basic groups: side effects depending on drug dose or type A, and side effect not depending on drug dose or type B. Also, based on the severity of the outcome, side effects are divided as mild, moderate, severe and lethal. The age group with the highest number of side effects reportings is 41 to 64, predominantly women. According to pharmacotherapeutic groups, the largest number of side effects reportings are for antimicrobial drugs, then non-steroidal anti-inflammatory drugs and drugs for the treatment of cardiovascular system. Reporting a side effects is a duty of healthcare professionals which allows safer use of the medication and thus prevents future side effects. Registration of the adverse reaction is done by using an application form sent to the Agency for Medicines and Medical Products. Severe side effects require abortion of therapy, and others require assessment of risk and benefit of the drug that is used. In the treatment of side effects it is important not to add new medications, unless it is necessary, and to have a clear therapeutic goal.