# idiosyncratic reaction

> English word · Noun

## Definitions
1. A reaction to a medication that is unusual and unpredictable, specific to a particular person. Unlike allergy, it can occur on first exposure to the medication; unlike a side effect, it affects only very few individuals.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/idiosyncratic-reaction