Access to marijuana for both medicinal and recreational purposes in the United States has expanded rapidly in the last 25 years. Since California voted to legalize medical marijuana (MMJ) in 1996, 33 states have passed legislation for comprehensive medical marijuana plans, with 12 of those states fully legalizing marijuana for recreational use¹; as of early 2021, 3 additional states have passed recreational marijuana legalization bills, and an additional state has passed an MMJ bill.

Also, many dispensaries endorse the use of MMJ for the treatment of glaucoma. In Colorado, for example, more than half of surveyed dispensaries supported the use of MMJ for glaucoma management.² Thus, glaucoma providers are often faced with the question: “Doctor, I heard marijuana can lower my eye pressure and treat my glaucoma. Is that true?” Or more directly: “Can I have a prescription for medical marijuana to treat my glaucoma?”

Indeed, marijuana and its components are known to have ophthalmic effects. Early research performed in the 1970s and 1980s did show that inhaled delta-9-tetrahydrocannabinol (THC) can lower intraocular pressure (IOP). This IOP-lowering effect peaks between 60 minutes and 90 minutes after inhalation of THC and lasts about 4 hours. However, inhalation of THC is associated with hypotension, tachycardia, palpitations, and altered mental status.^3-6 Additionally, while there is inconclusive evidence linking chronic inhaled marijuana use with lung cancer, it has certainly been shown to induce chronic bronchitis and emphysema, as well as impairing the normal immune defense mechanisms in the lungs that can predispose patients to various and potentially serious infections.⁷ Importantly, due to intensive breeding and a change in growth practices, the concentrations of THC have increased significantly over the years. While early research studies on the role of THC and IOP lowering utilized a drug concentration of 2.0% to 2.8%, a recent survey found that the average THC content in cannabis products promoted by dispensaries for medicinal use was 19% and often higher.⁸ Additionally, cannabidiol (CBD) products are now purchasable online and at retail stores, despite the fact that CBD remains on the Schedule 1 controlled substance list by the US Drug Enforcement Agency.^9,10 Studies have shown that the oral intake of CBD can actually increase IOP, a finding that should concern glaucoma providers whose patients may be purchasing these products at their local grocery or health food stores.

The American Glaucoma Society (AGS), American Academy of Ophthalmology (AAO), and the Canadian Ophthalmological Society (COS) have all published statements excluding MMJ as an acceptable treatment option for glaucoma. This is in part due to its side effect profile, as well as limited evidence that treatment with medical marijuana affects the long-term disease course of glaucoma.^11-13 Glaucoma providers, and ophthalmologists in general, should in theory be well educated about the limited role of MMJ in the management of glaucoma. So how big of an issue is this for providers and patients? Are glaucoma providers frequently asked about MMJ? What gaps of knowledge need to be addressed?

We surveyed members of the AGS to assess their attitudes and perceptions on the use of MMJ in the management of glaucoma via an electronic survey. Among the survey respondents, 37% reported having patients who cited using MMJ for their glaucoma, and 38% of respondents were asked about MMJ by their patients at least once per week. Further, 55% of respondents had patients who had explicitly asked them for MMJ prescriptions. With increasing legal access to marijuana across the country for both medicinal and recreational purposes, there has clearly been a concurrent increase in curiosity among patients with glaucoma about the role of MMJ as a treatment option. Importantly, the legal status of MMJ may not deter a patient from using it to treat their glaucoma; this factor is concerning for patients in states without regulated MMJ programs who may be using unregulated marijuana products for glaucoma management that may be contaminated with various other compounds that are dangerous as well.

Oral THC administration has been studied as a possible route of administration for IOP lowering as well. A 2006 study evaluated the efficacy of low-dose oral THC (5mg) in lowering intraocular pressure.¹⁰ Results showed that oral administration of THC did in fact significantly lower IOP; however, 50% of participants experienced adverse events, including oral pain, dizziness, hypotension, nausea, panic, and photopsias. Additionally, oral THC preparations are dependent on first-pass metabolism through the liver, leading to variably lower peak plasma concentrations as well as longer delays to peak concentrations in the body.¹⁴ Further studies must be performed to evaluate the efficacy and safety of oral THC administration for IOP lowering on a larger scale.

Perhaps most importantly, only 14% of providers kept information on MMJ in their office, and it is unknown what content is provided by these practitioners. A study performed in Washington, DC, found that roughly 60% of glaucoma patients had heard about the use of marijuana for treatment of their glaucoma. Where are these patients getting this information? It is possible, even likely, that these patients are receiving information from sources other than their physicians or ophthalmologists that is inconsistent with the recommendations from medical professional societies.

So, where do ophthalmologists go from here? Yes, inhaled THC has been shown to reduce IOP — there may be a role for development of treatment options targeting cannabinoid receptors in the eye in the future for glaucoma management. However, at the current time, glaucoma providers should counsel their patients against the routine use of MMJ as a treatment, which is in line with current recommendations from the professional societies. Further educational information should also be made available to patients in the office regarding the role of MMJ in glaucoma management, especially given the extensive sources of misinformation that can be accessed by patients outside of their visits with their ophthalmologist. GP

Zachary Bergman, MD, is an ophthalmology resident at the University of Maryland School of Medicine in Baltimore, Maryland. He reports no related disclosures.

Omolola Idowu, MBChB, is an associate professor in the department of ophthalmology and vision sciences and the director of the glaucoma fellowship at the University of Maryland School of Medicine. She reports no related disclosures.

Mona Kaleem, MD, is an associate professor of ophthalmology at Wilmer Eye Institute of Johns Hopkins University in Baltimore, Maryland. She reports no related disclosures.

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