Wiktionary
n. (context pharmacy medicine English) 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.
Usage examples of "idiosyncratic reaction".
His known idiosyncratic reaction to the drug, so historically useful in evading hostile interrogation, also made it impossible for him to use it to clear himself of any accusation.
His known idiosyncratic reaction to the drug, so historically useful in evading hostile interrogation, also made it impossible for him to use it clear himself of any accusation.
An idiosyncratic reaction to the anesthetic left her in a coma, with her vital signs sinking fast.
This can't be more than an idiosyncratic reaction to a kind of trauma that isn't likely to hit me again in my life.
She had entered a hospital in late 2000 for minor surgery, but an idiosyncratic reaction to the anesthetic left her in a coma, with her vital signs sinking fast.