blood flow to the optic nerve, counteracting the benefits of reducing IOP. Finally, their short duration of effect means that marijuana-based medicines must be taken up to eight times a day, which most patients are unlikely to do; other medicines reduce IOP equally well and need only be taken once or twice a day. This is an important difference because patients need to control IOP continuously due to the progressive nature of glaucoma.

It is possible that future research could reveal a therapeutic effect for isolated cannabinoids other than THC or produce synthetic cannabinoid analogs that last longer and have fewer side effects. But the most promising line of research for treating glaucoma lies in the development of therapies that can protect or rescue the optic nerve from damage or that can restore its blood supply. There is some evidence that a synthetic cannabinoidlike compound known as HU-211 has nerve-protecting properties, although it does not reduce IOP. HU-211 is chemically similar to THC, but it is not found in the marijuana plant and does not bind to the cellular receptor in brain cells that THC activates.

There is no question that marijuana-based medicines can be used to lower IOP. But like several other glaucoma medications that have fallen into disuse, their drawbacks outweigh their benefits. This was not the case when the first reports of marijuana's effects on IOP were published in the 1970s, a time when relatively few drugs —all of which caused troubling side effects—were available to treat the condition. Those drugs have since been superseded by more effective and less problematic medications. That seems the likely fate of marijuana-based treatments for glaucoma as well.

NOTE

1. Institute of Medicine. 1999. Marijuana and Medicine: Assessing the Science Base. Washington, DC: National Academy Press, pp. 203-204.



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