A cannabinoid CB1 receptor antagonist (Kis = 224 and >10,000 nM for CB1 and CB2, respectively); selective for CB1 over α1- and α2- adrenergic, D1 and D2 dopamine, benzodiazepine, histamine H1, GABA, 5-HT, and muscarinic receptors; reverses the inhibition of forskolin-induced cAMP accumulation induced by arachidonoyl ethanolamide (anandamide); reverses inhibition of light-induced phase shifts in hamsters induced by the CB1 agonist CP 55,940 when used at a dose of 1 mg/kg