Side effects are unintended consequences of a particular action, especially of medications. They are often regarded as adverse or undesirable effects that may occur in response to a treatment or intervention. Synonyms for the term "side effect" are secondary effects, after-effects, by-effects, unintended consequences, consequences, and unforeseen outcomes. These synonyms emphasize the unpredictability and often negative connotation of side effects. Other synonym suggestions include collateral damage, repercussion, spin-off, and residual effects. In most cases, side effects are mild and temporary, but in some cases, they can be severe and even life-threatening, thus it is essential to consider the potential risks when undergoing a particular treatment or medication.