For decades it has been accepted that marijuana can be used to treat glaucoma, an eye condition that can lead to blindness.
However, new research shows that while THC can help treat glaucoma, another ingredient in cannabis, CBD, has the opposite effect and can undermine the efficiency of THC.
Glaucoma is damage to the optic nerve that is caused by higher than normal pressure in the eye. For years, scientists have known that THC can help lower this pressure. However, a study released this month in the journal Investigative Ophthalmology & Visual Science found that CBD can counteract that.
“It has been known for nearly 50 years that cannabis and the psychoactive constituent [THC] reduce intraocular pressure,” study authors wrote. Previous study have suggested that CBD has no effect on eye pressure, but this study found different results. “Far from inactive, CBD was found to have two opposing effects on ocular pressure, one of which involved antagonism of tonic signaling. CBD prevents THC from lowering ocular pressure.”
Lead researcher Alex Straiker, of Indiana University’s Bloomington College of Arts and Sciences’ Department of Psychological and Brain Sciences, said that the results show the need for more research, and caution when using marijuana or cannabis products to treat individuals from glaucoma or other conditions.
“This study raises important questions about the relationship between the primary ingredients in cannabis and their effect on the eye,” he told Science Daily. “It also suggests the need to understand more about the potential undesirable side effects of CBD, especially due to its use in children.”
Straiker said that future research should examine how specifically the compounds in marijuana affect the brain.
“There were studies over 45 years ago that found evidence that THC lowers pressure inside the eye, but no one’s ever identified the specific neuroreceptors involved in the process until this study,” he said. “These results could have important implications for future research on the use of cannabis as a therapy for intraocular pressure.”
Researchers also found that THC and CBD affected eye pressure differently in male and female rats. Males who received THC had a much larger drop in their eye pressure, suggesting that there are sex differences in how the compound acts on the brain.
“This difference between males and females — and the fact that CBD seems to worsen eye pressure, the primary risk factor for glaucoma — are both important aspects of this study,” said Straiker. “It’s also notable that CBD appears to actively oppose the beneficial effects of THC.”