Glaucoma is a common cause of blindness.
Studies in the early 1970s showed that marijuana, when smoked, lowered intraocular pressure (IOP) in people with normal pressure and those with glaucoma. In an effort to determine whether marijuana, or drugs derived from marijuana, might be effective as a glaucoma treatment, the National Eye Institute (NEI) supported research studies beginning in 1978. These studies demonstrated that some derivatives of marijuana transiently lowered IOP when administered orally, intravenously, or by smoking, but not when topically applied to the eye.
However, none of these studies demonstrated that marijuana—or any of its components—could lower IOP as effectively as drugs already on the market. In addition, some potentially serious side effects were noted, including an increased heart rate and a decrease in blood pressure in studies using smoked marijuana.