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Marijuana and Glaucoma: Understanding the Research in 2019

The ability to see the world around us is a precious gift, but as we age, the possibility that our vision will change is nearly a sure bet. According to, our risk of developing glaucoma increases with each decade after reaching age 40.

Glaucoma comes second to cataracts as the leading cause of blindness worldwide. Medical marijuana is used to treat various health conditions including, glaucoma, a disease of the optic nerve, which carries visual information from the eye to the brain. When the optic nerve is damaged, it can result in a person in vision loss or blindness.

What Is Glaucoma?

Glaucoma is a group of eye diseases that damage the optic nerve. It’s also one of the leading causes of vision loss and blindness.

According to the American Academy of Ophthalmology (AAO), glaucoma is the leading cause of blindness in people older than age 60. The organization also says early treatment can help prevent the condition. There are two types of glaucoma: primary open-angle glaucoma and angle-closure glaucoma, which is also known as “closed-angle glaucoma” or “narrow-angle glaucoma.”

Primary open-angle glaucoma is the most common of the two and is estimated to affect more than 2.5 million Americans. It happens over time as the eye fails to drain fluid. This causes eye pressure to build, which damages the optic nerve. As painful as this may sound, it’s actually not painful at all, according to the AAO. At first, a person with this condition likely will not notice any vision changes. However, it is called “the silent thief of sight” for a reason. Once changes in the eye have been noticed, the damage is usually severe.

Angle-closure glaucoma happens when the iris is very close to the eye’s drainage angle, and the iris can block the drainage angle, the AAO explains.

“You can think of it like a piece of paper sliding over a sink drain,” it writes. “When the drainage angle gets completely blocked, eye pressure rises very quickly. This is called an acute attack. It is a true eye emergency, and you should call your ophthalmologist right away, or you might go blind.”

This condition also develops slowly, but the following signs indicate that a glaucoma attack is underway:

  • Sudden blurry vision
  • Severe eye pain
  • Headache
  • Redness of the eye
  • Nausea, feeling sick to the stomach
  • Vomiting
  • Seeing rainbow-colored rings or halos around light sources

If not treated right away, angle-closure glaucoma can cause blindness.

There is no cure for glaucoma, and any damage to the optic nerve is irreversible. However, it is treatable. Effective control of glaucoma involves taking medication to lower intraocular pressure. These medications include eye drops or surgery. The method taken depends on what kind of glaucoma a person has.

Still, even these methods will not lower eye pressure for some patients, writes glaucoma specialist Henry D. Jampel, MD, MHS, for the Glaucoma Research Foundation.

Can Marijuana Help Treat Glaucoma?

Much has been written about the medical benefits of marijuana for chronic conditions such as arthritis, autism, cancer, Crohn’s disease, post-traumatic stress disorder, among many others. Glaucoma has also made this list, as there have been claims that marijuana can help people manage the eye condition.

“Glaucoma is frequently cited as a reason for the use of medical marijuana,” according to Marijuana as Medicine? The Science Beyond the Controversy, published by the National Academies Press. The eye condition once prompted the U.S. government to grant permission for compassionate marijuana use, according to the publication.

In the early 1970s, studies found that smoked marijuana lowered intraocular pressure in people who had normal eye pressure and those who had glaucoma. They also found that administering the substance orally or intravenously also lowered eye pressure. Marijuana, however, was not directly applied to the eye in these studies. Eye drops are the preferred route of administration for glaucoma treatments. But to date, an effective topical cannabis-based eye drop that has passed rigorous testing hasn’t been developed.

Patients also experienced euphoria as an acute effect. These findings led the National Eye Institute (NEI) to begin research on the impact of medicinal marijuana on people with glaucoma in 1978. Observers point to this research on marijuana and glaucoma as the starting point of how the plant achieved what some say is mythical status about its effects; others view them as ground zero for later efforts to legalize marijuana use.

Marijuana plants in a dimly lit room

In 2019, however, the ongoing research into whether marijuana is an effective treatment for glaucoma remains either unclear or a mixed bag, depending on the source. While there have been claims that the substance can effectively treat glaucoma, reports about the specific benefits of it are not widely supported by scientific evidence.  Also, “There has been little research into the chronic use of marijuana to treat glaucoma,” writes Thomas A. Graul, M.D., for Glaucoma Today, which has left the question of whether this is a viable treatment up in the air as research continues.

This does not mean there’s been no research to suggest that medical marijuana could help relieve symptoms of glaucoma. Still, the results noted in these studies are not widely understood. In one account, researchers were unable to explain exactly how marijuana and cannabinoids reduce intraocular pressure.

One important finding that came out of this research is how long the effects of marijuana use lasted. The Marijuana as Medicine report highlights that most trials conducted in the 1970s found that “a single dose of marijuana or cannabinoid maintained this effect for three to four hours.” 

Several decades later, this short three- to four-hour window is still a concern among some in the professional medical community for various reasons. One reason is the effects of smoking marijuana regularly on one’s health.

“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,” glaucoma specialist Craig J. Chaya, MD, told the University of Utah for its January 2019 report. “Smoking so much of it daily would leave you too impaired to drive, or operate equipment, or function at the peak of your abilities. Obviously, this is not a good idea—for those and lots of other reasons.”

According to the Marijuana as Medicine report, the short pain relief that marijuana-based medicines produce means they must be taken up to eight times a day, something most patients will find challenging to do.

Despite the growing support for and legalization of marijuana use for medical purposes, it is still a mood-altering substance that acts upon the body in ways that do not make an ideal fit for everyone.

Effects of Marijuana on Body Raise Concern

As of November 2018, 33 states and the District of Columbia have legalized marijuana for medical or recreational use. And data show that more Americans are in favor of legalization. Despite U.S. public opinion that marijuana isn’t as harmful as drugs such as alcohol, heroin, cocaine, meth, or even prescription opioids such as OxyContin, the plant is a Schedule 1 drug in the United States, which means its abuse potential is high, and so is the possibility of developing a chemical dependence on it.

Marijuana, the dried and crushed or shredded parts of the cannabis plant, contains more than 400 chemicals, but tetrahydrocannabinol or THC is the primary ingredient responsible for how it affects the brain. The drug also has several effects on the body, both short-term and long-term. Short-term effects include:

  • Dizziness
  • Shallow breathing
  • Increased appetite, thirst
  • Dry mouth
  • Red eyes and dilated pupils
  • Slower reaction time
  • Hallucinations
  • Memory problems
  • Increased anxiety, paranoia

Long-term effects of marijuana use include:

  • Memory loss
  • Respiratory problems
  • Decline in IQ
  • Concentration issues
  • Addiction

Marijuana also lowers blood pressure, which Jampel explains could reduce blood supply to the optic nerve, which can cause further harm.

“Therefore it is possible that even though marijuana does lower the eye pressure, its use could conceivably make the vision loss from glaucoma worse!” he said. “For this reason, marijuana cannot be recommended without a long term clinical trial that evaluates the health of the optic nerve as well as the eye pressure.”

The physical and psychological side effects are among the reasons some observers are not in favor of using marijuana-based treatments to treat glaucoma.

Marijuana as Medicine states:

“Marijuana reduces blood pressure and produces psychological effects that some people—particularly the elderly—find intolerable. Several patients in these studies also reported that their hearts pounded or raced and that they felt uncomfortably anxious after taking cannabinoids.

“All of these effects could prove especially problematic for people at risk for cardiovascular disease and stroke; moreover, reduced blood pressure could decrease blood flow to the optic nerve, counteracting the benefits of reducing IOP.”

One study found that eight to 10 marijuana cigarettes would have to be smoked daily to control glaucoma for 24 hours, and smoking that much marijuana for the long term can increase the risk of lung cancer. Chronic marijuana use can also cause tolerance, which means once the body is used to it, the user may take it in higher amounts, which can lead to a psychological dependence that can be difficult to end. When someone becomes psychologically dependent on marijuana, consequences often follow.

These side effects that compromise users’ health has led to organizations issuing official statements that discourage the use of marijuana as a medical option to treat glaucoma.

In June 2014, the American Academy of Ophthalmology Complementary Therapy Task Force said it found “no scientific evidence demonstrating increased benefit and/or diminished risk of marijuana use in the treatment of glaucoma compared with the wide variety of pharmaceutical agents now available.”

Alternatives to Marijuana for Glaucoma

Anyone who wants to explore the option of medicinal marijuana for the treatment of glaucoma is strongly encouraged to talk with a physician or ophthalmologist or other eye specialist who can offer an informed, professional opinion. There are other standard treatment options for treating this set of eye diseases without the use of marijuana.

The Mayo Clinic reports that glaucoma treatment often starts with prescription eye drops that can help decrease how much fluid the eye makes. Several kinds of eye drops can be prescribed for this purpose. You can read about those here. Doctors also may prescribe oral medications, such as a carbonic anhydrase inhibitor, which comes in either a tablet or an extended-release capsule. The medication should be taken as directed.


Patients with glaucoma who are interested in marijuana-based treatments are strongly advised to consult with their physician or eye specialist about whether it is a suitable alternative treatment. This education and counseling should include transparency about the debate over such treatment.

“Patients should be counseled and informed about the lack of any scientific evidence demonstrating superiority of cannabis over other currently available pharmaceutical agents for glaucoma that are already approved by the FDA and extensively studied,” writes Glaucoma Today.

While “marijuana legalization, for medicinal or recreational purposes, has grown, but researchers said there has been a disconnect between actual research-supported uses for the drug and popular expectation of what it can do,” writes Maureen Duffy for VisionAware.

Research continues as to whether marijuana is a suitable and effective treatment for glaucoma. However, its side effects, health complications, and short duration of effectiveness are all factors to take into consideration before embarking upon such treatment.


(January 25, 2019). Glaucoma and Marijuana: What Ophthalmologists Want You to Know. University of Utah. from

Berdahl, John, MD. Glaucoma: Symptoms, Treatment and Prevention. All About Vision. from

Heiting, Gary, OD. How Vision Changes As You Age. All About Vision. from

(March/April 2018). Graul, Thomas A., MD. Marijuana and Glaucoma. from

(November 7, 2018). State Marijuana Laws in 2018 Map. Governing. from

Hartig, Hannah, Abigail Geiger. About Six-in-Ten Americans Support Marijuana Legalization. Pew Research Center. from

(October 29, 2017). Jampel, Henry D., MD, MHS. Should You Be Smoking Marijuana to Treat Your Glaucoma? Glaucoma Research Foundation. from

(December 29, 2015). Duffy, Maureen. New Research on Marijuana Use for Glaucoma: Is Education Enough, or Is Emotional Support also Necessary? VisionAware™. from

(September 2015). Facts About Glaucoma. The National Eye Institute. from

(2000). Mack A, Joy J. Marijuana as Medicine? The Science Behind the Controversy. from

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