Purpose: To study the effect of inhaled cannabis on intraocular pressure (IOP) in healthy adult subjects.

Design: Prospective, double-blind, randomized, placebo-controlled trial. Methods: Study participants were randomized to receive a single dose of inhaled cannabis or placebo in an 11:3 ratio. Subjects self-administered inhaled cannabis or placebo cigarette in negative-pressure rooms. Measurements of IOP, systemic blood pressure and plasma tetrahydrocannabinol levels were taken at baseline and every 40 minutes for 2 hours, and afterwards, every hour for 3 hours. A linear mixed-effects models and Wald tests were performed on the IOP readings and systemic blood pressure measurements to compare the treatment group with the placebo group, and with baseline readings, using p-value significance of alpha ≤0.05.

Results: A total of 14 participants were included. Average baseline IOP for the treatment group and placebo group was 17.5 mmHg and 18.4 mmHg, respectively, and did not significantly differ between the groups. IOP was significantly lowered from baseline in the treatment group at all time points post-treatment, up to the 4-hour time point (p<0.01). The placebo group had extensive IOP fluctuations and had a significant IOP reduction only at the 80-minute, 3-hour and 5-hour time points (p<0.05). Peak IOP lowering occurred at the 80-minute time point with 15.7% reduction in IOP in the treatment group. There were no significant changes in systemic blood pressure during the duration of the study.

Conclusions: Cannabis lowers IOP significantly from baseline in adult healthy subjects. This effect is detected from 40 minutes post-treatment and lasts up to 4 hours. Systemic blood pressure was not significantly affected.