Cannabis for glaucoma first made headlines in the 1970s, when there weren’t a lot of appealing medications on the market. At the time, cannabis promised fewer side effects and an impressive ability to reduce intraocular pressure (IOP).

Now, half a century later, there has been considerable research into what THC can do for IOP, but it has also revealed a few limitations. Yet, even after all this time, the interest remains, especially among patients seeking advice directly from budtenders instead of ophthalmologists.

What progress has been made in our understanding of this alternative therapy? And, is there a future where cannabis for glaucoma is a viable option?

What Is Glaucoma?

Briefly, glaucoma is an eye condition, or rather a group of conditions that impact people over 40. According to Mayo Clinic, it can “damage the optic nerve, the health of which is vital for good vision. This damage is often caused by abnormally high pressure in your eye.” This pressure is known as intraocular pressure or IOP.

There are approximately three million people with glaucoma in the US, and globally it is the leading cause of blindness. Unfortunately, there is currently no cure, and frustratingly, the early stages of the disease are often undetectable. 

Cannabis for Glaucoma, Offering an Alternative

In the 1970s, researchers discovered that treatment with cannabis, specifically THC, could reduce IOP. At the time, this was an exciting discovery, considering the less-than-ideal therapies on the market.

Nearly 50 years later, we still haven’t nailed down the mechanism of action. However, there is an assumption that “activating the CB1 receptor may be associated with an effect on IOP, indicating a possible mechanism of action for cannabis in the treatment of glaucoma,” as a 2019 literature review explained. 

Small, randomized controlled trials using all manner of THC-rich products (joints, oral products, cannabis concentrates, or even applied topically via eye drops) have demonstrated that this cannabinoid temporarily reduces IOP. Notably, CBD tends to have the adverse effect of increasing ocular pressure. 

The studies performed thus far have not compared conventional pharmaceutical treatments with the effects of cannabis. To date, all study designs were against a placebo. Also, with most of the notable studies (1980, 1981, 2001, 2006) completed decades ago, there was less attention paid to specific cannabinoid profiles, including CBD, than we would likely denote today.

Although cannabis for glaucoma may be one of the plant’s most well-known applications, it technically hasn’t been given a lot of scientific attention since the early 2000s. At the time of writing, there was only one clinical trial on record: “The Effect of Dronabinol on Ocular Hemodynamics in Patients With Primary Open Angle Glaucoma.” It interestingly used dronabinol, a synthetic THC product.

Limitations of Using Cannabis to Treat Glaucoma

Despite the widespread perception that cannabis effectively treats IOP and pain related to glaucoma, many organizations, including the Glaucoma Research Foundation and Glaucoma Today, strongly advise against its use. 

Since the early research, newer studies have clarified the limitations of cannabis. Cannabis may have had fewer and less egregious side effects when compared with the other pharmaceutical options in the 1970s, but modern glaucoma medicines are far less problematic.

Today, the major concerns about using cannabis are, rather interestingly, the side effects. Especially for an older demographic who are most susceptible to glaucoma, the mood-altering and sometimes psychological effects of cannabis can be challenging. Other rare side effects include hypotension, tachycardia, and palpitations. 

Perhaps the biggest challenge for patients seeking alternative treatment for glaucoma is the need to maintain a constant reduction of IOP. Cannabis does reliably reduce IOP; it does so for short spurts rather than offering long-term relief.

According to one study published in 2006, five milligrams of THC reduced IOP for four hours (other publications have reported the need for much higher doses, up to 20 mg every few hours). Patients would need to dose eight times throughout the day, or eight to ten joints over 24 hours based on four-hour effects.

Treating Glaucoma with Cannabis Requires a New Approach

With the strong evidence of benefit but notable limitations, where does this leave us in 2022? A recent 2019 literature review revealed that “the quality of available literature is poor.” Studies have so far have been highly variable in terms of controls, participants, and routes of administration.

With the largest limitation being the temporary nature of THC’s effects, new approaches and, most importantly, new administration routes should be reviewed. Precision dosing technology already exists that can slowly release cannabinoid therapies over a prolonged period. Testing the value of THC in combination with thermal patches or other devices could improve upon the current limitations.

Cannabis for Glaucoma Deserves More Scientific Study

There are somewhere between 60 to 80 million people worldwide diagnosed with glaucoma, and it remains a leading cause of blindness with no known cure. Any potential therapies should be on the table, especially with the advances in pharmaceutical delivery technologies. 

Cannabis holds potential so long as its limitations are addressed. That means determining the appropriate dose, side effect profile, and the development of a convenient slow-release formula and/or device. All of which is not outside the realm of possibility.