Sidebar: Discussing Medical Marijuana with Glaucoma Patients
With the adoption of medical marijuana laws by many states, glaucoma patients are naturally interested in whether marijuana can help preserve their vision. The conversation between the physician and patient can be tricky. After decades of political and cultural strife over the drug’s use, deeply entrenched notions confuse the issue. At one extreme, marijuana is a nefarious “gateway drug.” At the other, it is a “natural remedy” that is completely safe and useful for almost any malady.
Many glaucoma patients desperately desire new treatments, because they fear they are going blind. My goal is to discuss medical marijuana truthfully, succinctly, and in a manner that strengthens trust between the doctor and patient. I welcome the inquiry and respond, “I’m glad you asked. Many people are wondering whether marijuana might be helpful.” I quickly describe the mechanics of glaucoma and explain that marijuana can lower eye pressure. Next, I give my professional opinion: “Unfortunately, in its current state, smoking marijuana is not useful for the vast majority of glaucoma patients. The pressure drop does not last long enough, and smoking marijuana has dangerous effects throughout the body.” Finally, I offer hope: “The drug is being researched and has great potential. It is already used as a pill for anorexia and nausea in diseases like cancer. We may soon have a marijuana-based medicine for glaucoma, but we do not have it yet.”
I ask patients whether they are already using marijuana, and if so, I ask them to avoid the practice in the hours before appointments, as it will confuse my evaluation of medical or surgical efficacy. When further discussion seems useful, I elaborate on marijuana’s potential and why smoking it is a poor choice for glaucoma therapy:
Inhaled tetrahydrocannabinol (THC) lowers IOP from 25% to 33% in two-thirds of subjects, an effect comparable to the best glaucoma eye drops. Clearly, THC may someday be a powerful treatment option for glaucoma.1
The IOP effect peaks at 2 hours and lasts only 3 to 4 hours, meaning continuous IOP control would require smoking marijuana six or more times daily.1
The psychoactive effects of continuous marijuana consumption would impair normal function.
Both the volume of marijuana and the concentration of THC within cigarettes vary widely. As a result, the THC that a patient receives and its IOP effects will also vary unpredictably.
THC can lower blood pressure, which may worsen glaucomatous neuropathy through hypoperfusion injury.2
Smoke inhalation causes or exacerbates diseases such as asthma, emphysema, pneumonia, lung cancer, and heart disease.
When discussing with patients marijuana for glaucoma therapy, I strive to provide a multifaceted view. THC has enormous potential. Marijuana’s status as a schedule I narcotic has discouraged research for decades, but someday, this drug may be a powerful addition to our glaucoma regimen as a topical, oral, or depot-type agent. Currently, however, inhaled medical marijuana is not indicated for the vast majority of glaucoma patients.
David Diaz, MD, is a glaucoma specialist at the University of Vermont in Burlington, Vermont. Dr. Diaz may be reached at firstname.lastname@example.org.
- Green K. Marijuana smoking versus cannabinoids for glaucoma therapy. Arch Ophthalmol. 1998:116;1433-1437.
- Kaufman PL. Marijuana and glaucoma. Arch Ophthalmol. 1998:116;1512-1513.