In pharmacology, an inverse agonist is an agent which binds to the same receptor binding-site as an agonist for that receptor but exerts the opposite pharmacological effect.
One particular example is R015-4513 which the inverse agonist of the benzodiazepine class of drugs (such as Xanax and Valium). R015-4513 and the benzodiazepines both utilize the same GABA binding site on neurons, yet R015-4513 has the opposite effect, producing severe anxiety rather than the sedative effect the benzodiazepines.