In biochemistry and pharmacology, an allosteric modulator (allo- from the Greek meaning "other") is a substance which indirectly influences (modulates) the effects of an agonist or inverse agonist at a target protein, for example a receptor. Allosteric modulators bind to a site distinct from that of the orthosteric agonist binding site. Usually they induce a conformational change within the protein structure. A positive allosteric modulator (PAM) or allosteric enhancer induces an amplification of the orthosteric agonist's effect, either by enhancing the binding affinity or the functional efficacy of the orthosteric agonist for the target protein. A negative modulator (NAM) reduces the effects of the orthosteric ligand, but is inactive in the absence of the orthosteric ligand. Substances that occupy the allosteric binding site and are functionally neutral are called silent allosteric modulators (SAMs). Classic benzodiazepines are well-known PAMs.