Cannabis for Glaucoma: Still Effective but Still Impractical After Decades of Research | Research

The takeaway

Cannabis effectively lowers eye pressure, but its cardiovascular and neurological side effects at the same dose may actually undermine the benefit by reducing blood flow to the eye.

Read this if you use or are considering cannabis for glaucoma and want to understand the medical evidence.

Marijuana potency rose from ~2-3% THC (1970s) to ~20% (2016), but glaucoma pharmacology remains unchanged.

What the researchers found

This review examined the current state of cannabis for glaucoma treatment against a backdrop of increasing marijuana potency and legalization. The core pharmacology has not changed since the 1970s and 1980s: cannabis is an effective ocular hypotensive agent, meaning it reliably lowers pressure inside the eye.

However, the same dose that lowers eye pressure also produces cardiovascular effects (including lowered blood pressure) and neurological effects. Lowered systemic blood pressure can reduce blood flow to the optic nerve, which could theoretically cancel out or even reverse the benefit of lower eye pressure.

The review noted that marijuana potency has increased dramatically, from about 2-3% THC in the 1970s to approximately 20% at the time of writing.

Why it matters

Glaucoma remains one of the most commonly cited reasons for medical marijuana use, despite the medical community's longstanding concerns about its practical limitations. This review clearly articulates the paradox: cannabis lowers eye pressure but may simultaneously reduce the blood flow needed to protect the optic nerve, potentially negating the benefit.

The numbers in context

Marijuana potency increased from approximately 2-3% THC in the 1970s to approximately 20% by 2016. Many US states had passed laws allowing medicinal or recreational use by the time of publication.

How the study worked

This was a narrative review published in Current Opinion in Ophthalmology, summarizing the current evidence on cannabis and glaucoma in the context of expanding legal access. The author reviewed existing pharmacological evidence and clinical considerations.

What this study cannot tell us

This is a narrative review, not a systematic review. It reflects one author's interpretation of existing evidence. The review does not address newer cannabinoid formulations or delivery methods that might avoid systemic side effects, such as topical eye drops.

How to read the evidence

Moderate evidence based on decades of established pharmacological research, summarized in a narrative review format.

When this study was published

Published in 2016. The fundamental pharmacology has not changed, though newer cannabinoid delivery methods continue to be explored.

The bigger picture

Glaucoma was one of the original medical conditions that drove early marijuana legalization efforts. Decades later, the pharmacology supports that cannabis works for eye pressure, but the clinical reality is more complicated than the simple narrative suggests. Modern glaucoma treatments offer targeted pressure reduction without the systemic side effects cannabis produces.

Questions still open

Could cannabinoid eye drops lower eye pressure without systemic side effects? Does the cardiovascular effect of cannabis actually worsen glaucoma outcomes in real patients? How do patients who use cannabis for glaucoma compare in disease progression to those using standard treatments?

Common questions

Does cannabis help glaucoma?

Cannabis does lower eye pressure, which is the main treatment target for glaucoma. However, it also lowers blood pressure throughout the body, which may reduce blood flow to the optic nerve and counteract the benefit. Most ophthalmologists do not recommend it as a primary treatment.

Why don't doctors recommend cannabis for glaucoma?

The pressure-lowering effect is short-lived (requiring dosing every few hours), produces psychoactive and cardiovascular side effects, and the blood pressure reduction may actually harm the optic nerve. Modern eye drops provide longer-lasting, targeted pressure reduction without these issues.

Read the original research

Cannabinoids for treatment of glaucoma.

Current opinion in ophthalmology, 27(2), 146-50

View on PubMed ↗Publisher’s paper ↗

Citation

Novack, Gary D. (2016). Cannabinoids for treatment of glaucoma.. Current opinion in ophthalmology, 27(2), 146-50. https://doi.org/10.1097/ICU.0000000000000242