What is "tachyphylaxis"

n. (context medicine English) A rapidly decreasing response to a drug following administration of the initial doses

Tachyphylaxis ( Greek ταχύς, tachys, "rapid", and φύλαξις, phylaxis, "protection") is a medical term describing an acute rapid decrease in response to a drug after its administration. It can occur after an initial dose or after a series of small doses. Increasing the dose of the drug may be able to restore the original response.