Glaucoma is a condition in which elevated pressure inside the eye, called intraocular pressure (IOP), damages the optic nerve—causing vision loss and eventual blindness if not treated. In 1971, it was first reported that smoking marijuana, or cannabis, could temporarily lower your IOP. The amount of smoking that would be necessary to maintain that lowered pressure, though, is neither safe nor sustainable. 

Unlike tetrahydrocannabinol (THC), which is found in marijuana, cannabidiol, or CBD, does not have psychoactive effects. CBD has becoming increasingly available for medical use across the U.S., and research about its therapeutic properties and ability to treat a variety of conditions, including glaucoma, has increased exponentially from just a few years ago. 

Multiple studies have shown that THC, the psychoactive ingredient in marijuana, is what reduces IOP. Most studies have also found that CBD does not affect IOP at all. The results from a 2018 study conducted at Indiana University, however, have contested those findings.*

What they did

A total of 85 male and female mice were kept on a 12-hour light/dark cycle. The mice were between three and eight months old. 

The researchers applied THC and CBD topically to the eyes of living mice. They then retested the mice’s IOP using tonometry, a process also used on humans, in which a pen-like device is gently pressed against the eye lens after the eye has been anesthetized.

What they found

The team found that a single topical application of eye drops containing only THC lowered IOP by approximately 28% for eight hours. The effect of the same treatment in female mice was more limited, lasting for only four hours, with no evident effect at the eight-hour mark.  

CBD, on the other hand, raised IOP by 18% for at least four hours after the drops were applied.

It was also found to interfere with the IOP-reducing mechanisms of THC and canceled out THC’s therapeutic effects.

What it means

While several companies are working to develop cannabinoid-based therapies to treat glaucoma, this latest study demonstrated that the mechanisms by which THC and CBD affect IOP are complex, and further research is necessary. 

Until a new intervention is shown to consistently lower eye pressure with fewer side effects than the standard interventions (eye drops, laser therapy, and traditional surgery), experts recommend that glaucoma patients adhere to their prescribed treatments. 

*Shelton, B. (2019, Feb. 5). CBD Oil May Worsen Glaucoma. American Academy of Ophthalmology. https://www.aao.org/eye-health/news/cbd-oil-may-worsen-glaucoma

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