Glaucoma is a condition characterized by increased pressure within the eye. This can cause damage to the blood vessels and nerve endings that carry impulses to the optic nerve, which can impair vision. If this is chronic (open-angle glaucoma) and pressure is slowly increased over time, there can be loss of peripheral vision and problems seeing in the dark. If it is acute (closed-angle glaucoma) the pupil may become dilated and fixed and immediate medical attention is required. The incidence of glaucoma increases with age and has a genetic predisposition. It is usually treated with medicated eye drops.
Glaucoma and Cannabis
NOTE FOR FIRST TIME READERS: Cannabinoids – such as THC, CBD – and terpenes are the main medically active components in cannabis (aka marijuana). For more information on these components, and much more about the plant, see our section on the Science of Cannabis.
It was first observed that cannabis reduces intraocular pressure during a 1971 systematic investigation on healthy cannabis users. It was found that some derivatives of marijuana lowered the intraocular pressure (IOP) when taken intravenously, by smoking or orally, but not when applied topically to the eye. Because it required constant inhalation of marijuana, as often as every three hours, it was not recommended to use cannabis to treat glaucoma as the ensuing side effects significantly outweighed the benefits.
Cannabis decreases IOP by an average 25-30%, occasionally up to 50%. Some non-psychotropic cannabinoids, and to a lesser extent, some non-cannabinoid constituents of the hemp plant also decreases pressure. The specific mechanism in cannabis that causes this is not known.
Cannabis treatments for glaucoma have mostly been in combination with eye drops, as the effects seem to be additive. A non-psychoactive extract of cannabis was tested in combination with Timolol eye-drops in patients with high IOP in 1980. They found that the effects of the two medications were complementary and were beneficial in some cases where other medications had failed. More testing needs to be done to determine how and when cannabinoids are indicated in the treatment of glaucoma.
With patients who use cannabis to treat glaucoma it’s been shown that chronic use does not have to be administered every 3 hours for long-lasting eye pressure reduction. But THC does seem to be more effective than CBD.
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