In 2005, the first evidence was obtained that the cannabinoid CB(1) receptor contains an allosteric binding site. The site can be recognized by synthetic small molecules, which display a markedly divergent effect on orthosteric ligand affinity versus efficacy; these small molecules are allosteric enhancers of agonist binding affinity and allosteric inhibitors of agonist signalling efficacy. Allosteric modulation heralds a new approach to the manipulation of the endocannabinoid system for therapeutic benefit; it promises to augment the existing portfolio of selective direct agonists, competitive antagonists and enzyme inhibitors.