Nabilone is a synthesized crystalline benzopyran that resembles the cannabinols but is not a tetrahydrocannabinol. Oral administration of 0.5 to 2 mg to patients with open-angle glaucoma reduced the intraocular pressure from 10% to 54% with an average of 28%. Administration of a topical ophthalmic nabilone solution (0.1 mg/drop) to both eyes of adult albino rabbits (1.5 to 3.5 kg) lowered the IOP an average of 25%. The peak action of the nabilone administered in this manner was 60 minutes, with a return to normal IOP by 180 minutes. Tolerance developed in rabbits after one week of topical administration.