A side-effect is any effect other than an intended primary effect. It may or may not be expected, and it may be adverse or beneficial. It is a term often used in the following fields:

1. In medicine, with regard to drugs or medical procedures; see adverse effect (medicine);
2. In laws and regulations, to describe its unintended effects;
3. In computing; see side-effect (computer science).

See also

• Unintended consequence
• Collateral damage