Tachyphylaxis

Tachyphylaxis is a medical term describing an acute (sudden) decrease in the response to a drug after its administration. Tachyphylaxis can occur both after an initial dose of medication or after an inoculation with a series of small doses. Increasing the dose of the drug may be able to restore the original response. This can sometimes be caused by depletion or marked reduction of the amount of neurotransmitter responsible for creating the drug's effect, or by the depletion of receptors available for the drug or neurotransmitter to bind to. This depletion is caused by the cell's reducing the number of receptors in response to their saturation. Examples: Amphetamine, ephedrine, MDMA (indirectly acting drugs). The term comes from the Greek words tachys (rapid), and φύλαξις phylaxis (protection).