If you were hoping that CBD, or cannabidiol, would offer a natural glaucomaremedy, the latest research is a downer. A new study suggests that CBD doesn’t lower eye pressure, it raises it. That’s bad because high eye pressure is the primary risk factor for glaucoma, one of the leading causes of blindness in the United States.

Glaucoma is a condition that damages the optic nerve at the back of the eye. It’s the nerve that transmits visual information to the brain, allowing us to see. Glaucoma is often linked to a buildup of pressure inside the eye. The increased pressure can damage the nerve, leading to permanent vision loss.

For their study, researchers from Indiana tested an eyedrop in rats that contained CBD, a component of cannabis that does not get you stoned. They found that it raised pressure inside the eyes by 18 percent for at least four hours after the drops were instilled. They also tested CBD’s more famous cannabinoid cousin, THC (tetrahydrocannabinol), the component that does get you stoned. Eyedrops containing only THC decreased eye pressure by up to 30 percent within eight hours.

Researchers also found that THC and CBD affected eye pressure differently in male and female rats. Males who received THC had a much larger drop in their eye pressure, suggesting that there are sex differences in how the compound acts on the brain. 

What does this all mean? It shows there is a need for more research, and caution when using marijuana or cannabis products to treat glaucoma or other conditions. 

Since it was first reported in 1971 that smoking marijuana could lower eye pressure, the plant has attained near mythical status as a miracle drug for glaucoma. And as 33 states, the District of Columbia, Guam and Puerto Rico have approved medical marijuana/cannabis programs, more patients are asking their ophthalmologists about it.

So, why don’t the American Academy of Ophthalmology and the American Glaucoma Society support its use? Short answer: because it has some serious limitations and possible risks.

While it’s true that smoking marijuana can reduce pressure inside the eye, it remains a suboptimal treatment because people with glaucoma require 24-hour pressure control to prevent vision loss. You would need to smoke marijuana eight to 10 times a day, every day; a treatment regimen that would make it difficult to hold down a job or drive, not to mention the potential cost. The potency of marijuana also varies considerably, and there’s not enough research currently available to know the optimal dose for each patient or how it interacts with other medications.

Then there are the side effects. It can cause the heart to beat faster and decrease blood pressure, which can reduce blood flow to an already compromised optic nerve. Smoking marijuana long-term may increase the risk of lung cancer. And one study showed that some people can build up a tolerance to marijuana’s eye pressure lowering effects.

But some researchers are undeterred. One company, Nemus Bioscience, is working to develop a cannabinoid-based therapy for glaucoma. Until a new therapy can show it works to consistently lower eye pressure with fewer side effects than the standard treatment of eyedrops, laser surgery and sometimes incisional surgery, ophthalmologists continue to recommend patients stick with their prescribed therapy and come in for regular visits, so they can monitor their long-term care.