Myths in Medicine - Medical Marijuana and Glaucoma

Glaucoma is an indication for medical marijuana, right?

Probably False.  

Glaucoma is a medical condition, more common in the elderly, in which the intraocular pressure (IOP) is abnormally elevated.  This increased IOP is a result of a blockage of the outflow of the aqueous humor.  Worldwide, glaucoma exists as a common cause of blindness as a high IOP can compromise nutritional flow to the optic nerve.    

Tetrahydrocannabinol (THC) reduces the IOP through an unknown mechanism by as much as 24%; however, this effect is relatively transient - only 3 or 4 hours according to an Institute of Medicine (IOM) paper published in 1999.  Glaucoma is typically a chronic condition deemed primary open angle glaucoma and therefore the aim of treatment is a reduction in the IOP during the course of the entire day. Thus, in order to effectively treat glaucoma with THC an individual would have to smoke or ingest marijuana 6-8 times daily.  The pharmaceutical industry has made billions working to formulate medicine for infrequent dosing due to poor patient compliance.  

Currently, we have treatments that effectively decrease IOP that have few systemic side effects and good efficacy.  Parasympathomimetic drugs like pilocarpine contract the iris sphincter, resulting in an increase in outflow of the aqueous humor. Prostoglandin F2alpha analogs such as Latanoprost increase the outflow of the aqueous humor and require a mere drop in each eye daily.  

For a more thorough evaluation of this subject, check out a recent episode of ToxTalk by UMass at iTunes or here.

Note:  This is not an endorsement for or against medical marijuana but merely a look at some of the evidence on one aspect of this expansive subject.

References:

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