Tachyphylaxy

Tachyphylaxis is a term indicating the rapid disappearance of the drug's effect on the organism when it is repeatedly administered at short intervals. It is a type of habit that only lasts as long as the drug is in the body.

Example
Ephedrin increases blood pressure. The effect gradually weakens after repeated administration. Ephedrine acts on vascular smooth muscle indirectly, by washing out noradrenaline mediators from the presynaptic terminal. Along with the decrease in mediator, the effect of ephedrine also decreases.

Effect
It follows from the above that if the drug in question is known to be subject to tachyphylaxis and does not produce a sufficient effect in the given clinical situation, it is not advisable to repeat its administration in a short time interval.