Medical marijuana shows promise in treating many ailments. Recent research suggests glaucoma may not always be one of them. The findings are worrisome because glaucoma is frequently cited as a condition that would benefit from medical marijuana treatment.
In a paper published in the journal Investigative Opthamology & Visual Science (December 2018) researchers at Indiana University revealed that cannabidiol, or CBD, may cause a rise in eye pressure that persists for hours after use among some subjects. Intraocular pressure rose 18 percent and remained elevated for at least 4 hours after CBD use. Although CBD is not the only chemical component of marijuana, this revelation has troubling implications for two reasons:
1) CBD has a history of being considered inactive compared to other components and
2) new plant strains have been developed that are skewed, sometimes heavily, toward CBD.
Perhaps more significantly, the study, which was conducted using mice, not humans, also found that when used in combination CBD blocked tetrahydrocannabinol, or THC has been demonstrated to lower the pressure inside the eye. Results also indicated gender played a role in how effective THC is in reducing intraocular pressure.
For over 45 years, THC has been known to lower inner eye pressure; however, the specific neurotransmitters involved in reducing pressure had not previously been identified. The Indiana University study confirms that THC, not CBD, is the chemical component responsible for lowering pressure inside the eye. The results also indicated that THC has a weaker effect on females than on males. Specifically, the research showed that 4 hours after ingesting THC, the inner eye pressure of male mice declined by 22 percent. Four hours later the decline was almost 30 percent. In contrast, female mice experienced a decrease of just 17 percent 4 hours after ingestion and no reduction at all after 8 hours, suggesting females may be less susceptible to the effects of THC.
These results, especially the identification of the neurotransmitters affected by THC and CBD, may have significant implications on future research into medical marijuana therapies even beyond glaucoma. Individuals suffering from, or at risk of developing, glaucoma who are undergoing any medical marijuana therapy, as well as those using it to treat glaucoma, should consult their physician or ophthalmologist and may wish to consider switching to a strain with higher levels of THC, particularly if they are female. The research conducted by Indiana University did not overturn nearly 50 years of medical history, but it did raise questions. Additional caution may be called for in addition to more research.