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Glaucoma is an eye disease usually associated with an increased fluid pressure inside the eyes that damages the optic nerve, leading to vision loss or even blindness. The most common form of the disease—chronic, open-angle glaucoma—is a leading cause of blindness in the United States and the number one cause of blindness in African Americans.
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.
A wide variety of therapies are currently used to treat glaucoma, including FDA-approved drugs and laser and conventional surgery. Research to date has not investigated whether marijuana use offers any advantages over currently available glaucoma treatments or if it is useful when used in combination with standard therapies.
The identification of side effects from smoked marijuana, coupled with the emergence of highly effective FDA-approved medications for glaucoma treatment, may have led to diminished interest in this research area.
Workshop on the Medical Utility of Marijuana--Report to the Director, NIH, by the Ad Hoc Group of Experts