CBD Won’t Reduce IOP
Cannabidiol (CBD) oil may be “on trend” along the reclaimed-wood paneled shelves of spiritual-healing apothecaries across the country, but its impact on intraocular pressure (IOP) may be less than ideal. Although the cannabis plant—from which CBD is derived—is popularly believed to lower pressure, the particular chemical extract connected to that effect may actually be rendered powerless by application of CBD oil, according to newly published research.
Investigators affiliated with the Gill Center for Biomolecular Science and the Department of Psychological and Brain Sciences at Indiana University say their study, which appears in the December Investigative Ophthalmology & Visual Science, shows that, while Δ9-tetrahydrocannabinol (THC) can lower IOP, CBD can actually interfere with that effect. THC, the team explained, affects IOP by activating two receptors—CB1 and GPR18—and that this response was much stronger in the male mice tested than the females. But the focus of the investigation was to understand the impact of the cannabis plant’s less psychoactive element: CBD. Interestingly, the CBD acted as a negative allosteric modulator at CB1, essentially raising IOP and cancelling out any of the benefits achieved from THC.
“The regulation of ocular pressure by THC and CBD is more complex than previously appreciated,” the authors explain. “THC acts via a combination of CB1 and GPR18 receptors in a sex-dependent manner, while CBD can both raise IOP and interfere with the effects of THC. The potential of CBD to elevate ocular pressure should be evaluated further as a potential deleterious side effect, particularly with long-term use.”
How Medical Marijuana Treats Glaucoma
Cristian Zanartu, MD, is a licensed board-certified internist who has worked for over five years in pain and palliative medicine.
Many people are wondering about the possible use of marijuana instead of eye drops to treat glaucoma. Glaucoma is a disease of the optic nerve, the nerve cable that connects the eye to the brain. Glaucoma can cause significant vision loss and even blindness. Most types of glaucoma coexist with high pressure inside the eye. Limited research has shown that marijuana could potentially treat glaucoma because of its ability to lower the pressure in the eye.
An eye doctor's main goal in the treatment of glaucoma is to lower eye pressure to a safe level in order to halt damage caused by the high-pressure levels. Treatment typically includes prescribing medications, using laser treatments, or surgery.
Most glaucoma patients are treated with topical medication eye drops that lower the pressure in the eye to a level where the glaucoma does not progress. Unfortunately, some people do not tolerate daily eye drops very well and additional glaucoma therapies are sought.
Marijuana's Effect on Glaucoma
As several more states attempt to legalize the use of marijuana for medicinal uses, it has become a hot topic for glaucoma patients as some studies have shown that smoking marijuana can lower eye pressure, both generally and in people that suffer from glaucoma. People who cannot tolerate typical glaucoma medications might be able to use marijuana to effectively lower their eye pressure.
Downsides of Smoking Marijuana
Scientists have found that marijuana does lower eye pressure but the effects only last for 3 or 4 hours. This means that to lower eye pressure adequately, marijuana would have to be smoked every 3 hours.
Because marijuana causes mood-altering effects, smoking it every 3-4 hours would be impossible for people who drive for a living, operate heavy machinery, or have jobs that require close attention to detail.
Also of great concern is that marijuana cigarettes contain chemical compounds that can damage the lungs similar to regular tobacco cigarette smoking. Studies also show that chronic use of marijuana can have unwanted and sometimes permanent effects on brain function.
Marijuana Eye Drops
If the harmful effects of marijuana are mainly caused by inhalation, could doctors administer the active ingredient, THC (tetrahydrocannabinol), in a different way? Scientists have conducted studies in which patients ingested THC through oral (by mouth) or sublingual (under the tongue) methods and also in topical eye drops.
Although oral or sublingual methods avoid lung problems, they have other unwanted side effects. Because glaucoma is a chronic disease, unwanted systemic side effects make THC a poor option for treatment.
While eye drops sound like the most logical method of taking the drug, THC is not very water-soluble. As a result, it has been difficult to develop an eye drop with high enough concentrations of THC to be effective.
If oral THC could be tolerated, more long-term studies are needed to make sure that it will not worsen glaucoma. Research has shown that some glaucoma is worsened by a lack of proper blood flow to the optic nerve. Marijuana actually reduces blood pressure so it is possible that marijuana could worsen the glaucoma by making the optic nerve receive less blood flow.
On the other hand, recent research shows that marijuana may not only treat glaucoma by reducing eye pressure, but it may also act on certain receptors to provide a type of neuro-protection against damage to the optic nerve. This would treat glaucoma in a different way, and it is worth conducting further studies.
Until then, researchers are focusing on a better way to make a THC formulation that people can tolerate and that will have a longer duration of action. For now, glaucoma patients should stick with doctor recommended traditional glaucoma medications.