Drug side effects may refer to
- Adverse effect (medicine), an unintended, and undesirable, consequence of any kind of medical treatment
- Adverse drug reaction, an unintended consequence specifically arising from drug therapy
- Side effects (drug)
- Therapeutic effect, a desirable consequence of any kind of medical treatment, even though resulting as an unintended, unexpected consequence of the treatment
For particular side effects see Category:Side effects (drug)