+An **adverse reaction** is any undesirable or unintended response to an intervention, such as a [Drug](/wiki/drug) or medical procedure. It goes beyond a simple [Side Effect](/wiki/side_effect), often implying harm or an unexpected negative outcome.
+## See also
+- [Drug](/wiki/drug)
+- [Side Effect](/wiki/side_effect)
+- [Allergy](/wiki/allergy)
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