In glaucoma, cannabis and THC have been shown to reduce intra-ocular pressure (IOP) by an average of 24% in people with normal IOP who have visual-field changes. In studies of healthy adults and glaucoma patients, IOP was reduced by an average of 25% after smoking a cannabis “cigarette” that contained approximately 2% THC—a reduction as good as that observed with most other medications available today, according to a review by the Institute of Medicine.[90]

In a separate study, the use of cannabis and glaucoma was tested and found that the duration of smoked or ingested cannabis or other cannabinoids is very short, averaging 3 to 3.5 hours. Their results showed that for cannabis to be a viable therapy, the patient would have to take in cannabis in some form every 3 hours. They said that for ideal glaucoma treatment it would take two times a day at most for compliance purposes from patients.[91] Due to these limitations, the American Glaucoma Society, in a statement in 2009, did not recommend marijuana yet as a viable glaucoma treatment, even if it expressed hope that “marijuana or related compounds could protect the optic nerve not only through IOP [intra ocular pressure] lowering but also through a neuroprotective mechanism.”