H(eye) – or Low?
Two chemical components; opposite effects. How medical marijuana impacts glaucoma for better – and for worse.
Phoebe Harkin | | Quick Read
Scientists have known that cannabis reduces ocular pressure since the ‘60s, but the reason why has remained a mystery. But now, a team at the University of Indiana have delved into the endogenous cannabinoid signaling system and made an unexpected discovery – the drug’s two major chemical components, THC and CBD, counteract. While THC, the primary psychoactive ingredient, was found to lower eye pressure, CBD appeared to block its effect. Moreover, CBD appeared to worsen the primary underpinning of glaucoma by causing a rise in intraocular pressure (IOP) (an average of 18 percent for at least four hours after use). So what does this mean for patients being treated with medical marijuana? “Given the popular embrace of CBD and its recent approval for childhood epilepsy, this potential rise in IOP is a side effect that we should be aware of,” says lead author Alex Straiker, an associate scientist from the university’s Department of Psychological and Brain Sciences.
Straiker and his team used knockout mice to separate neuroreceptors in a bid to understand more about the conflicting effects of THC and CBD. They found that three different cannabinoid-related receptors – CB1, GPR18 and GPR119 – all regulate ocular pressure independently. Moreover, they identified CB1 and GPR18 as those susceptible to pressure lowering.
Interestingly, the study also found that the THC’s effect was sex-dependent; male mice experienced an average drop in eye pressure of nearly 30 percent four hours after exposure to THC alone, along with a lower pressure drop of 22 percent after hours. On the other hand, female mice experienced an average pressure drop of just 17 percent after four hours, with no difference in eye pressure after eight hours.
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