Fig. 2.

Allosteric modulators may either increase or decrease the effect of an agonist or an antagonist. An allosteric enhancer can be a more physiologic alternative to synthetic agonists (b, c). An allosteric enhancer can only act in the presence of an (endogenous) agonist. It mimics the duration and intensity of action of a hormone or neurotransmitter (a) much better than a synthetic agonist does (c). This combined action of two compounds (i.e., agonist and enhancer) might also induce selectivity of drug action