There are several types of glaucoma, the most common of which is primary open-angle glaucoma (POAG). POAG causes optic nerve damage as a result of increased intraocular pressure. The disorder is the number one cause of blindness in African-Americans in the United States, and roughly 2.5 million Americans have glaucoma. The Foundation of the American Academy of Ophthalmology and the National Eye Institute consider marijuana (Cannabis sativa) an alternative and potentially ineffective treatment for the disorder, though many have touted its medicinal properties in recent legal battles over personal cannabis use.
Evidence for Treating Glaucoma with Cannabis
The National Eye Institute conducted studies on the effects of marijuana on POAG from 1978 to 1984 and found that smoking or ingesting marijuana transiently reduces the intraocular pressure; topical application had no effect. However, the effect was short-lived, lasting only three to four hours, and it was not found to be as beneficial as the FDA-approved pharmaceuticals used to treat the disorder. Throughout the 1990s, panels of experts were gathered by the institute to discuss external studies (those not conducted by the NEI) on the topic. The conclusions were the same as those made in 1984 - that the drug is needed in too high of a dose and its effects are not beneficial enough. However, there is anecdotal evidence from patients who do not respond to FDA-approved treatments.
Side Effects and Risks of Treating Glaucoma with Cannabis
One of the reasons the NEI and American Academy of Ophthalmology have given for not further pursuing studies on marijuana is the side effects observed in the NEI studies, including a faster heart rate and lower blood pressure, as well as acute euphoria. Other stated risks of cannabis use are somewhat controversial, such as associations with cancer from smoking and hallucinogenic or addictive properties of the drug.
Approved Marijuana Derivatives for Treating Disease
Currently, only a handful of states in the U.S. allow medical marijuana use, though it is still a schedule I drug on the federal level, meaning that its use is illegal for treating glaucoma. The active components of cannabis are THC and cannabidiol, cannabinoids that activate receptors in the brain. Cannabinoid receptors are also present in the retina. THC has been shown to reduce intraocular pressure, whereas cannabidiol has an opposing effect.
One synthetic cannabinoid, a THC derivative, is approved by the FDA for use in the United States – Marinol. Another synthetic is approved in Canada, Sativex, which is a derivative of both THC and cannabidiol, a more recently identified active ingredient in marijuana. Clinical trials are ongoing in the U.S. Acomplia, a cannabinoid receptor antagonist, has been approved in the European Union, but has been shown to have gastrointestinal side effects and was pulled from clinical trials in the U.S. However, none of these drugs are approved for treating glaucoma.
References:
American Academy of Ophthalmology Complementary Therapy Task Force. “ Marijuana in the Treatment of Glaucoma ”, revised April 2003; accessed January 17, 2010.
National Eye Institute, National Institutes of Health. “NEI Report: Glaucoma and Marijuana Use”, revised May 13, 2009; accessed January 17, 2010.
Tomida et al. Effect of sublingual application of cannabinoids on intraocular pressure: A pilot study. Journal of Glaucoma, 15(5), 2006.
Yazulla. Endocannabinoids in the retina: From marijuana to neuroprotection. Progress in Retinal and Eye Research, 27(5), 2008.
Alicia Mae Prater - Alicia received her doctorate in Experimental Pathology in 2007. She has been a freelance writer and scientific editor since 2008.
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