The scientists reported that one of the primary problems involved in glaucoma is too much intraocular pressure (IOP). "The goal of glaucoma therapy is to decrease IOP, as lower IOP has been shown...to slow the progression of glaucoma." The study reported that, overall, scientific evidence regarding cannabis for glaucoma is limited and that a common problem in studies conducted to date is small sample sizes (cohorts) that do not involve enough test participants.
It analyzed five prior randomized controlled trials that tested cannabis "as an IOP-lowering agent." These five studies involved a variety of consumption avenues among the participants, including smoked cannabis, topical drops, sublingual oromucosal spray, and oral capsules.
In one study, glaucoma patients were administered cannabis joints that contained two percent delta-9 tetrahydrocannabinol (THC). The researchers noted a reduction in IOP that lasted for approximately three hours. However, the study also reported a number of side effects from the treatment, including altered perception and severe hypotension. The current study determined that this investigation "found statistical significance in IOP reduction using smoked cannabis."
The same researchers conducted a follow-on study with the goal of determining variance in efficacy from different consumption avenues. The scientists were particularly interested in lowering the incidence of adverse side effects from the smoked cannabis and employed eye drops containing either delta-9 THC or a placebo (0% for placebo, 0.05%, or 0.1% THC in light mineral oil).
The follow-on study observed, "no significant difference between the three treatments as the mean ± standard deviation for the treatment groups' IOP measurements overlapped at all measurement times." The scientists added that one limitation of this investigation was a potentially inadequate period (24 hours) during which the medication could take effect.
The study reported that the literature review observed a number of adverse events in the study participants, including "altered sensation, dizziness, nausea, hunger, and drowsiness." The most severe side effects noted were rapid heart rate (tachycardia) combined with anxiety and severe hypotension (abnormally low blood pressure).
The report concluded that prior studies about the potential efficacy of cannabis for glaucoma have revealed that the herb may possess the ability to lower IOP, but that the quality of the data produced by these scientific investigations is "poor."
"The studies that were reviewed were highly variable in their methods and patient population selected, and therefore no current evidence supports the use of any form of cannabis to replace existing therapy for glaucoma," declared the scientists.
They reported that all cannabis consumption avenues involved a short duration of action, meaning that glaucoma patients would necessarily have to indulge in "frequent dosing," but that such consumption patterns feature the potential to "reduce patient adherence and increase side effects of the medication."
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