Should marijuana be indicated for glaucoma?

A recent editorial in TheJournal of the American Medical Association (JAMA) raised some questions about the indications for medical marijuana, which vary greatly by state.

“There is some evidence to support the use of marijuana for nausea and vomiting related to chemotherapy, specific pain syndromes, and spasiticity from multiple sclerosis,” Deepak Cyril D’Souza, MBBS, MD, and Mohini Ranganathan, MD, write. “However, for most other indications that qualify by state law for use of medical marijuana, such as hepatitis C, Crohn disease, Parkinson disease, or Tourette syndrome, the evidence supporting its use is of poor quality.”

Another one of those diseases for which there is little evidence to support it being an indication for medical marijuana? Glaucoma.

Related: Marijuana's role in optometry and beyond

Glaucoma and medical marijuana

Medical marijuana is legal in 23 states and Washington, DC. As Drs. D’Souza and Ranganathan note, the indications vary widely.

“There are inconsistencies in how medical conditions are qualified for medical marijuana use within a state and between states,” they write. “For example, in Connecticut, psoriasis and sickle cell disease but not Tourette syndrome qualify, even though the supporting evidence for all three conditions is uniformly of very low quality…These differences reflect inconsistences in evaluating and applying current evidence toward decision making about qualifying indications for medical marijuana use.”

Glaucoma is an indication for a medical marijuana prescription in the following states:

• Alaska

• Arizona

• California

• Colorado

• Connecticut

• Washington, DC

• Hawaii

• Illinois

• Maine

• Massachusetts

• Michigan

• Minnesota

• Montana

• Nevada

• New Hampshire

• New Jersey

• New Mexico

• Oregon

• Rhode Island

• Washington

Next: What would you do?

What would you do?

But as we’ve reported before, not only is the evidence to support glaucoma as an indication pretty slim, some eyecare professionals say it could actually do more harm than good for a glaucoma patient.

When Optometry Times spoke to Bob Prouty, OD, FAAO, for our 420 special report (for those who do not partake, April 20 is something of an unofficial stoner holiday), he said that while medical marijuana holds a lot of promise several diseases and conditions, glaucoma isn’t one of them-at least for now, based on available research.

Related: Marijuana and optometry: Practicing post-legalization

Some studies from the 1970s found that marijuana lowered intraocular pressure (IOP) for a few hours, but the mechanism is still unclear. The problem, Dr. Prouty says, is that marijuana also lowers blood pressure, which could decrease profusion of the optic nerve, which makes it more fragile.

And marijuana lowers IOP for only three to four hours at a time, meaning a patient would need to be toking up around the clock in order to achieve the results of current glaucoma therapies.

Optometrists are not allowed to prescribe medical marijuana, but theoretically, ODs in any of the states listed above could have glaucoma patients who have a prescription for medical marijuana.

Optometry Times Editorial Advisory Board member Michael Chaglasian, OD, chief of staff at the Illinois Eye Institute, says he would be surprised and upset if non-eyecare physicians prescribed medical marijuana for a condition they were not treating. If that were the case, he says he would contact both the prescribing physician and the patient and try to educate them.

“I’d probably try to compromise with the patient: ‘Take medical marijuana if you want, but realize that topical glaucoma mediation is much better at treating your condition. Is it worth risking your vision for? At least continue to take all of your prescribed medication and see me regularly,’” says Dr. Chaglasian. “And I would probably increase the frequency of visual field and OCT testing to look for signs of progression.”

Next: Should ECPs work to get glaucoma off the indication list?

Should ECPs work to get glaucoma off the indication list?

How did glaucoma even get on the medical marijuana indications list? The JAMA editorial provides some insight:

“For most qualifying conditions, approval has relied on low-quality scientific evidence, anecdotal reports, individual testimonials, legislative initiatives, and public opinion,” Drs. D’Souza and Ranganathan write. “Imagine if other drugs were approved through a similar approach.”

Dr. Prouty says that when the original studies were conducted in the 1970s, the only available treatments were Pilocarpine and oral Acetazolamide, both of which have significant side effects and were tough for patients to tolerate. And, at the time, there was a different understanding of what glaucoma was. 

"The treatment paradigm at that time was glaucoma was a high pressure problem that ultimately causes a visual field defect," he says. "We now know that glaucoma is an optic nerve problem in which the IOP may be a component of the disorder. So the IOP drove the understanding in the 70s, but today, the optic nerve drives the understanding. So lowering IOP was the approach." 

While it has been very difficult to study marijuana's effects on glaucoma due to its status as a Schedule 1 drug, we now have a better understanding of glaucoma and better treatment options, so Dr. Prouty says utilizing marijuana as a treatment is senseless. But this was apparently not considered when passing medical marijuana legislation across the country. 

"Given that it lowers IOP and was considered a possible treatment 40 years ago, it has almost been grandfathered into being considered for medical marijuana treatment," says Dr. Prouty. "But every medical professional who understands this stuff knows to not consider it for use/treatment. Since most of the MDs prescribing medical marijuana are not eyecare professionals-OMD, ODO, or OD-they have the old paradigm in mind and often a possible other motivation to prescribe it. Since we have no studies for them to reference, the treatment use persists. Patients will also continue to ask for it since they still think glaucoma is IOP problem." 

Both the American Academy of Ophthalmology and the American Glaucoma Society have stated that marijuana is not a proven treatment for glaucoma-but should the eyecare community be raising more awareness and work to get glaucoma off the indication list until further research is conducted?

Dr. Prouty has called for the American Optometric Association and the optometric community as a whole to come out against using medical marijuana for the treatment for glaucoma. 

Dr. Chaglasian says glaucoma should not be on the indications list, but he says it is a relatively minor concern when it comes to optometry’s political and legislative battles.

“I would support further research into the ocular/glaucoma-related benefits of marijuana, but frankly, no one is ever going to pay for that research,” he says.

Next: Many edible marijuana products are mislabeled

Many edible marijuana products are mislabeled

JAMA also recently published a research letter that found that the amount of tetrahydrocannabinol (THC) was mislabeled in the majority of edible medical marijuana products.

THC is responsible for marijuana’s psychological effects, but it is also used to prevent nausea and vomiting and increase appetites for people suffering from diseases like cancer or AIDS with the FDA-approved drug Marinol (dronabinol, AbbVie).

Researchers looked at 75 different products from 45 different brands. They found that only 17 percent were accurately labeled, while 23 percent were underlabeled, and 60 percent were overlabeled with respect to THC levels.

An estimated 16 percent to 26 percent of medical marijuana users consume these edible products.

“Even though oral consumption lacks the harmful by-products of smoking, difficult dose titration can result in overdosing or underdosing, highlighting the importance of accurate product labeling,” the authors write.

The mislabeling puts consumers at risk, the authors write. Products that are overlabled will not produce the desired medical benefit, while products that are underlabled are placing patients at risk of experiencing adverse effects.

“Edible cannabis products from three major metropolitan areas, though unregulated, failed to meet basic label accuracy standards for pharmaceuticals,” they write.

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