CBD Eye Drops: Do They Really Work?

First, The Bad News

THC has been a known treatment for glaucoma since as far back as the 1970s ^{4 Marijuana as Medicine? The Science Beyond the Controversy Mack A, Joy J. Marijuana as Medicine? The Science Beyond the Controversy. Washington (DC): National Academies Press (US); 2000. 9, MARIJUANA AND GLAUCOMA. Available from: https://www.ncbi.nlm.nih.gov/books/NBK224386/ Mack A, Joy J.} . How does marijuana help glaucoma? By reducing the eye pressure the disease is known for, THC has been shown to also reduce the risk of blindness caused by the disease.

The problem is, this effect is short-lived and requires regular doses of THC throughout the day, making this an unrealistic treatment option for patients who can’t, or simply don’t want to, manage their days with a constant high.

So, of course, researchers started to wonder if perhaps CBD could produce the same benefits without the high.

It could have been a perfect solution, if only CBD had performed in research studies similarly to THC. Instead, CBD eye drops for glaucoma were found to be ineffective at low doses, and potentially harmful at higher doses, increasing eye pressure rather than decreasing it ^{5 Effect of sublingual application of cannabinoids on intraocular pressure: a pilot study. Tomida I, Azuara-Blanco A, House H, Flint M, Pertwee RG, Robson PJ. Effect of sublingual application of cannabinoids on intraocular pressure: a pilot study. J Glaucoma. 2006;15(5):349-353. doi:10.1097/01.ijg.0000212260.04488.60 Tomida I, Azuara-Blanco A, House H, Flint M, Pertwee RG, Robson PJ} .

For this reason, the Food and Drug Administration (FDA) and the American Academy of Ophthalmology (AAO) have both issued warnings against using CBD for the treatment of glaucoma.

The Bright Side

The current research makes it clear CBD is not likely to ever be a viable treatment option for glaucoma. But could CBD eye drops still serve a different purpose?

Research from 2018 on mice with corneal injuries indicates reason for at least some hope. In this study, the behavioral responses of the mice being observed suggested that the topical application of CBD into their cauterized eyes actually helped to reduce their pain levels ^{6 The Cannabinoids Δ8THC, CBD, and HU-308 Act via Distinct Receptors to Reduce Corneal Pain and Inflammation. Thapa, D., Cairns, E. A., Szczesniak, A. M., Toguri, J. T., Caldwell, M. D., & Kelly, M. (2018). The Cannabinoids Δ8THC, CBD, and HU-308 Act via Distinct Receptors to Reduce Corneal Pain and Inflammation. Cannabis and cannabinoid research, 3(1), 11–20. https://doi.org/10.1089/can.2017.0041 Thapa, D., Cairns, E. A., Szczesniak, A. M., Toguri, J. T., Caldwell, M. D., & Kelly, M.} . Could the same be true for people with eye injuries?

Another study found that intraocular injections of CBD produced anti-inflammatory results for patients with uveitis, an inflammatory eye condition that can lead to blindness ^{7 Anti-inflammatory effects of cannabinoid CB(2) receptor activation in endotoxin-induced uveitis Toguri JT, Lehmann C, Laprairie RB, et al. Anti-inflammatory effects of cannabinoid CB(2) receptor activation in endotoxin-induced uveitis. Br J Pharmacol. 2014;171(6):1448-1461. doi:10.1111/bph.12545 Toguri JT, Lehmann C, Laprairie RB, et al} . Researchers declared the results promising, but concluded further studies needed to be done. Intraocular injections are also a far more invasive treatment option than CBD eye drops. Still, CBD has known anti-inflammatory properties, so future research may investigate the use of CBD eye drops in an effort to produce similar results ^{8 Cannabinoids as novel anti-inflammatory drugs. Nagarkatti, P., Pandey, R., Rieder, S. A., Hegde, V. L., & Nagarkatti, M. (2009). Cannabinoids as novel anti-inflammatory drugs. Future medicinal chemistry, 1(7), 1333–1349. https://doi.org/10.4155/fmc.09.93 Nagarkatti, P., Pandey, R., Rieder, S. A., Hegde, V. L., & Nagarkatti, M.} .

There are several other eye conditions to consider as well. Could CBD help treat macular degeneration? Or what about cataracts?

The answer is we just don’t know. Yet. The research still doesn’t exist to provide answers one way or another, but there is reason to believe CBD eye drops could eventually prove beneficial in treating certain ocular conditions.

Of course, knowing what we do know about the risks of CBD eye drops in the treatment of glaucoma makes it clear more research needs to be done before declaring CBD eye drops safe to use for other conditions.