When it comes to the medicinal uses of cannabis, one of the most often quoted claims is that it is an effective treatment in glaucoma. Indeed, it was one of the first government-approved uses of medical marijuana and remains one of the more popular reasons for Medical Marijuana prescriptions today. But how does marijuana help glaucoma, and how clear is the science on the topic?
Glaucoma is one of the leading causes of blindness in the world today, and better treatments are highly desired. Since the first study published in the observation that marijuana consumption reduced intraocular pressure in all patients tested, it has been viewed as a possible new treatment. Over the years, further studies have collaborated these claims, and also investigated the mechanisms through which cannabinoids could affect eye health.
How Cannabinoids Affect the Eyes
According to a review done in 2004 other effects identified included conjunctival hyperemia (inflammation, itching, burning) reduced tear production, and change in pupil size. Later studies made explored the specific cannabinoids involved in the observed actions and looked into the mechanisms which provided the drop in IOP. According to the 2004 review quoted above, it was originally theorized the observed effects of cannabinoids on IOP were a result of interaction with the endocannabinoid receptors of the central nervous system or a restriction of blood flow to the eye.
However, later studies using topical applications found they had the same results, and it was later found that the tissues of the eye actually contain CB-1 receptors that respond to exogenous and endocannabinoids. Other studies also indicated the neuroprotective, antioxidant, and vasorelaxant properties of THC and CBD as aiding in the fight against glaucoma. At the time, the promise for a scientific consensus on the use of cannabinoids in the treatment of glaucoma looked imminent. There were however some problems identified regarding cannabis in the treatment of glaucoma, the first being smoking.
Even in the first study by Hepler and Frank, the negative effects of smoking marijuana were pointed out, and most later studies echoed this opinion. Most researchers felt that the benefits of the effects on IOP did not justify the negative consequences of long-term marijuana smoking on lung health. Thus, it was identified that further studies were needed on alternate routes of administration.
Administering Cannabis For Glaucoma
The problem is that THC and the other cannabinoids are lipophilic, and do not dissolve in water. When used in eye drops, less than 5% of the cannabinoids are absorbed. Attempts to use mineral oils and other lipid substances have thus far proven ineffective, and most trials have been stopped due to irritation. Synthetic cannabinoids such as Sativex and Marinol have been used in some studies with some success, and there are also edibles or tinctures for more health-conscious patients. Despite these, however, the US FDA has still not approved cannabinoids in the treatment of glaucoma has it has done for anorexia and nausea and vomiting associated with chemotherapy and cancers.
Why Is Cannabis Not An Approved Treatment For Glaucoma?
Other than the issue of administration, other researchers have pointed out that cannabis has issues with efficacy and duration, and does not have advantages over other currently available glaucoma medications. A recent review published in 2016 pointed out that most ophthalmological organizations globally are in agreement that current data does not support the claims made.
The review cites a 1998 report from the Canadian Ophthalmological Society in which it was concluded that there was a ‘lack of evidence’, and later updated their statement in 2010 to say “The COS does not support the medical use of marijuana for glaucoma due to short duration of action, the incidence of undesirable psychotropic effects” and compared it to medical, laser, and surgical alternatives of treatment. This opinion was echoed by the American Glaucoma Society in 2010, and again in 2014 by the American Academy of Ophthalmology.
Should I Use Cannabis To Treat My Glaucoma?
Current scientific evidence does not justify the widespread and highly popularized claims made regarding cannabis in the treatment of glaucoma. However, this does not mean that it has no place in that treatment. Many patients with glaucoma are also using complementary medicines in conjunction with traditional glaucoma treatments, and there is no evidence to show that this is not effective or desirable. There is plenty of anecdotal evidence to show that patients get relief by incorporating cannabis into their treatment plan.
For patients that are not so concerned by the psychotropic effects or short duration of action, cannabis is a very attractive complementary medicine. If this is something you are interested in, you should have an honest conversation with your doctor about it and see how you can fit cannabis into your current treatment plan.