Marijuana, or Cannabis sativa, has been known to lower intraocular pressure (IOP) since the 1970s. The active component of marijuana, Δ9-tetrahydrocannabinol (THC), has been shown to lower IOP in animals and humans and in various formulations, including inhaled, oral, intravenous, sublingual, and topical. This article will address the reasons why marijuana is not recommended for the treatment of glaucoma.
The American Glaucoma Society published a position statement in 2009, stating, “Summary: Although marijuana can lower the intraocular pressure (IOP), its side effects and short duration of action, coupled with a lack of evidence that it use alters the course of glaucoma, preclude recommending this drug in any form for the treatment of glaucoma at the present time.” This article will address the reasons why marijuana is not recommended for the treatment of glaucoma.
Most patients who inquire about the use of marijuana as an alternative treatment are asking about smoking marijuana. There are many problems with this method of administration including the fact that the length of duration of its effect is about 3-4 hours. Therefore, in order to maintain an IOP-lowering effect, one would need to smoke 6-8 times a day. The effect of marijuana on the lungs, brain, and cardiovascular system, including but not limited to emphysema, impaired mental functioning, and heart and blood pressure problems, limits its use, especially when one considers the need to use it up to 8 times a day. The dosage frequency is particularly untenable when one considers that some glaucoma medications only require one dose each day. Furthermore, there is some evidence that tolerance can build up, with a rebound IOP elevation above baseline levels when treatment was discontinued. Lastly, marijuana lowers blood pressure, and as this can affect the amount of blood flow reaching the optic nerve, marijuana may actually have a detrimental effect in glaucoma despite the fact that it lowers IOP. These side effects are also relevant for other dosage forms, such as oral forms of synthetic THC, which also have the problem of varying and unpredictable absorption.
Topical THC eye drops seem to be a promising avenue to pursue, as one could maximize the drug’s effect at the site of action (the eye) and limit unwanted systemic side effects. However, because of its insolubility in water, the development of effective eye drops has not yet been achieved. Alternatives such as mineral oil have been tried but are not only irritating, but also can affect IOP. Other vehicles are under investigation, but to date no ocular formulation of THC of other active marijuana-derived compounds has been demonstrated to be consistently effective in lowering IOP.
Certainly, further research could yield promising results for topical THC eye drops. Indeed, when smoking marijuana was first demonstrated to lower IOP, the National Eye Institute did support research studies starting in 1978. However, none of these NEI-supported studies demonstrated that marijuana, or its derivatives, could lower IOP as effectively as FDA-approved glaucoma medications. Currently, there are no NIH sponsored studies on the use of marijuana to treat glaucoma. In conclusion, given marijuana’s short duration of action, systemic side effects, and lack of evidence supporting its benefit in the treatment of glaucoma by itself or compared to other FDA-approved glaucoma medications, its use is not recommended at this time.