idiosyncratic reaction

noun

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.

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Meanings

nounidiosyncratic reaction (plural idiosyncratic reactions)

plural idiosyncratic reactions

  1. pharmacymedicineA 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.

    The conclusion was that Mr Shakoor had experienced a rare and unpredictable idiosyncratic reaction to them.

    2001, Margaret Fordham, “The Standard of Care Applicable to Practitioners of Alternative Medicine: Shakoor v Situ”, in Singapore Journal of Legal Studies, page 4
Cite this entry
APA

idiosyncratic reaction. (n.d.). In WatkinsX Dictionary. Retrieved November 4, 2026, from https://dictionary.watkinsx.com/word/idiosyncratic%20reaction

MLA

“idiosyncratic reaction.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/idiosyncratic%20reaction. Accessed November 4, 2026.

Chicago

WatkinsX Dictionary, s.v. “idiosyncratic reaction,” accessed November 4, 2026, https://dictionary.watkinsx.com/word/idiosyncratic%20reaction.

Source: idiosyncratic reaction on Wiktionary, CC BY-SA 4.0.