A Synthetic Cannabinoid Eye Drop Lowered Eye Pressure in Treatment-Resistant Glaucoma | Research

The takeaway

A synthetic cannabinoid (WIN 55212-2) applied as eye drops reduced intraocular pressure by up to 31% in glaucoma patients who had not responded to conventional treatments.

Read this if you have glaucoma and have heard about cannabis as a treatment option.

31% maximum pressure reduction at 50-microgram dose

What the researchers found

The synthetic CB1 receptor agonist WIN 55212-2, applied topically to the eye, reduced intraocular pressure in 8 patients with glaucoma resistant to conventional therapies. At the 25-microgram dose, pressure decreased by 15% within 30 minutes and reached a maximum reduction of 20% at 60 minutes. At the 50-microgram dose, pressure decreased by 23% within 30 minutes and reached a maximum reduction of 31% at 60 minutes.

The researchers had previously demonstrated the presence of CB1 receptor mRNA and protein in the human ciliary body, establishing a biological mechanism for the pressure-lowering effect. These results confirmed that CB1 receptors directly regulate human intraocular pressure.

Why it matters

While cannabis has long been known to lower eye pressure, its use for glaucoma has been limited by short duration of effect and systemic side effects. This study demonstrated that a topical synthetic cannabinoid could achieve meaningful pressure reduction directly in the eye, potentially avoiding systemic effects. The fact that it worked in treatment-resistant patients made it particularly significant.

The numbers in context

Eight patients were treated. At 25 micrograms: 15% pressure reduction at 30 minutes, 20% maximum at 60 minutes. At 50 micrograms: 23% reduction at 30 minutes, 31% maximum at 60 minutes.

How the study worked

This was a small clinical study in which 8 patients with glaucoma resistant to conventional therapies received topical application of the synthetic CB1 agonist WIN 55212-2 at doses of 25 or 50 micrograms. Intraocular pressure was measured at 30-minute and 60-minute intervals after application.

What this study cannot tell us

The study included only 8 patients with no placebo control group. Duration of the pressure-lowering effect beyond 60 minutes was not reported. Long-term safety and efficacy of repeated dosing were not assessed. The study did not compare results with existing topical glaucoma medications.

How to read the evidence

This is a small pilot study with 8 patients and no placebo control, providing preliminary evidence of concept.

When this study was published

Published in 2001. Despite these results, cannabinoid eye drops have not become a standard glaucoma treatment.

The bigger picture

Despite these promising results, cannabinoid-based eye drops have not become a standard glaucoma treatment. The short duration of effect remains a challenge, as glaucoma requires 24-hour pressure control. However, this study established proof of concept for topical cannabinoid delivery to the eye and confirmed the role of CB1 receptors in regulating intraocular pressure.

Questions still open

How long did the pressure-lowering effect last beyond the 60-minute measurement? Could sustained-release formulations extend the duration of effect enough for practical glaucoma management? Why have topical cannabinoid eye drops not progressed further in clinical development?

Common questions

Can cannabis treat glaucoma?

Cannabis can lower eye pressure, but the effect is short-lived (about an hour in this study). Glaucoma requires constant 24-hour pressure management, making cannabis impractical as a standalone treatment with current formulations.

What makes this different from smoking cannabis for glaucoma?

This study used a targeted eye drop rather than systemic cannabis, which could avoid the psychoactive effects and other side effects of smoking. The eye drop delivered the cannabinoid directly to where it was needed.

Read the original research

The synthetic cannabinoid WIN55212-2 decreases the intraocular pressure in human glaucoma resistant to conventional therapies.

The European journal of neuroscience, 13(2), 409-12

View on PubMed ↗

Citation

Porcella, A; Maxia, C; Gessa, G L; Pani, L. (2001). The synthetic cannabinoid WIN55212-2 decreases the intraocular pressure in human glaucoma resistant to conventional therapies.. The European journal of neuroscience, 13(2), 409-12.