A new study suggests that marijuana may have a strange benefit: improving night vision. Based on a pharmacologist’s observation in the 1990s that Jamaican fishermen who smoked or consumed cannabis had “an uncanny ability to see in the dark,” researchers at McGill University dug in. They applied a synthetic cannabinoid to the eye tissue of tadpoles of an African toad and found, to their surprise, that it seemed to work. Specifically, they found that the cannabinoid made particular retinal cells more sensitive to light, improving the speed at which the eye responded to even dim stimulus, reports the Guardian. “We didn’t believe what we were seeing,” a study author told the Montreal Gazette. “The cannabinoids were increasing the excitability of cells in the eye that connects to the brain.”
Researchers then tracked tadpoles—only some of which had been given the cannabinoid—while showing them dark moving dots, which the tadpoles naturally avoid. All tadpoles performed well in the light. But in the dark, the cannabinoid tadpoles avoided significantly more dots than the others. If the same effect occurs in humans—a 2004 study found people had better night vision after smoking cannabis, but it didn’t explore why, per Science Alert— cannabis could theoretically be used to treat retinitis pigmentosa and glaucoma by protecting retinal cells.