Glaucoma and Cannabis: What Ophthalmologists Want You to Know
If you’ve heard that smoking marijuana can treat glaucoma, we have an important tip: the rumor isn’t true.
But experts at the John A. Moran Eye Center say they can direct you to the latest treatments that will safely and effectively treat glaucoma without leaving you high and dry.
Understanding Glaucoma and Treatments
Glaucoma is a complex eye condition that damages the optic nerve over time. If untreated, the disease can cause permanent vision loss and lead to blindness. Glaucoma, which affects more than 4 million Americans, is characterized by elevated pressure within the eye (known as intraocular pressure or IOP).
Glaucoma patients may have fluctuations in IOP throughout their lives, making it a challenging disease to manage.
For decades, the only way to control glaucoma and lower IOP levels has been through medication, such as prescription eye drops, or surgery—depending on the type of glaucoma and how severe it is.
After several studies conducted in the 1970s showed that smoking marijuana appeared to lower the pressure levels of people with glaucoma, patients were hopeful.
But that was then.
What More Research Revealed
Research funded by the National Eye Institute examined whether cannabis or its active ingredient (THC) could be safely used to keep IOP lowered.
Researchers found when subjects smoked marijuana [KM(1] or took a form of THC as a pill or by injection, it did lower IOP—but only for three to four hours.
And that's a .
“Glaucoma needs to be treated 24 hours a day, so you would need to smoke marijuana six to eight times a day, around the clock, to get the benefit of a consistently lowered IOP,” says Craig J. Chaya, MD, a glaucoma specialist at the Moran Eye Center’s . “Smoking that much marijuana would leave you unable to function normally. Obviously, that’s a problem.”
How Cannabis Impacts the Body
Other than a mood-altering effect, cannabis comes with other documented side effects. Two of those are especially concerning for glaucoma patients, such as:
- Tachycardia, or an abnormally high heart rate.
- Decreased blood pressure, which reduces blood flow to an already compromised optic nerve and effectively cancels out the benefit of the lowered IOP.
Research into THC eyedrops to treat glaucoma (only oil-based delivery methods can work with THC) revealed two major problems:
- The drops didn’t result in an IOP-lowering effect.
- The drops caused significant eye irritation.
Doctor Recommendations
Decades after the original 1970s research, patients still ask about treating their glaucoma with cannabis. Chaya refers them to the official position statement of the .
It concludes:
“Although marijuana can lower the intraocular pressure, its side effects and short duration of action, coupled with a lack of evidence that its use alters the course of glaucoma, preclude recommending this drug in any form for the treatment of glaucoma at the present time.”
Impacts of Legalization
Now that recreational and medical marijuana usage is legal in dozens of states—and the clinical benefits for certain conditions are well-documented—there are calls for more research.
In 2017, the National Academies of Sciences, Engineering, and Medicine published a that summarizes the research supporting the many therapeutic uses of cannabis, including negative effects and areas where additional research is necessary.
“For now, glaucoma patients should continue to follow their doctor's orders,” Chaya advises.
