Oral niacin can increase intraocular pressure.

The intraocular pressure of a 73-year-old man with a history of primary open-angle glaucoma had been approximately 21 and 17 mm Hg in the right and left eyes, respectively, while taking latanoprost 0.005% and dorzolamide hydrochloride 2%. When taking 500 mg of oral niacin (also known as vitamin B3 or nicotinic acid), his intraocular pressure increased to 37 and 27 mm Hg in the right and left eyes, respectively, on one occasion. On reexamination, the intraocular pressure had increased to 28 and 23 mm Hg in the right and left eyes, respectively. Each time the niacin was stopped, the intraocular pressure decreased to the original levels.