The pooled evidence does not support cannabis as a glaucoma treatment

Design

Systematic review and meta-analysis of mean differences, stratified by route

Population

5 studies, 99 patients (69 with THC exposure)

Primary outcome

Peak percentage reduction in intraocular pressure after THC

Effect

Overall 14.7%; intravenous 33.3%; oral/topical non-significant; vs control 6.9% (p=0.41)

Patients still ask whether cannabis can treat their glaucoma, on the strength of old reports that it lowers intraocular pressure. This meta-analysis pooled the available studies to put numbers on it.

Across five small studies (99 patients), the peak intraocular-pressure reduction after THC was about 15% overall, but almost all of that came from the intravenous route (33%), which is not a treatment anyone would use. Oral and topical routes produced small, non-significant falls, and when compared directly with control the pooled reduction was 6.9% and not statistically significant.

The practical answer for the clinic is clear: cannabis is not a usable glaucoma therapy. Any pressure effect is brief, route-dependent and, by practical routes, no better than control, so it cannot replace proven pressure-lowering drops or surgery. Tell patients this plainly, and redirect them to adherence with established treatment.

• Peak intraocular-pressure reduction after THC was about 15% overall, but 33% came from the intravenous route alone.
• Oral (10.7%) and topical (9.4%) routes gave small, non-significant reductions.
• Versus control, the pooled reduction was 6.9% and not statistically significant (p=0.41).
• Counsel patients that cannabis is not a usable glaucoma treatment and reinforce proven pressure-lowering therapy.

Why it matters

It gives a clear, evidence-based answer to a common patient question and prevents substitution for effective therapy.

Don't overread it

Only five small studies — this shows no usable glaucoma benefit, not that cannabinoids have no biological effect on pressure at all.

The statistics, in plain English

The headline 15% reduction is misleading because it is driven by the intravenous route no one uses; by oral or topical routes the confidence intervals cross zero, meaning no reliable effect, and against control the difference was not significant.

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