Growing up, you likely learned about a list of veggies, including Vitamin-A rich carrots, that can improve your eyesight, but marijuana probably wasn’t on that list. Now, researchers from the Montreal Neurological Institute suggest smoking weed may help your night vision by decreasing the eyes’ sensitivity to light.

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The belief marijuana could improve, not impair, vision goes against conventional wisdom. One of the drug’s key effects on eye health is redness. THC, the drug’s active ingredient, lowers blood pressure, which dilates the blood vessels and increases blood flow to the body. This leads the blood vessels in the eye to expand and causes redness or bloodshot eyes. But researchers found applying a synthetic cannabinoid to eye tissue can make cells more sensitive by increasing the rate they fired to both bright and dim light stimuli.

“Initially you distrust yourself when you see something that goes against widely held ideas, but we tried the experiment so many times, using diverse techniques, and it was a consistent result,” said Ed Ruthazer, senior author of the paper, and a professor of neurology and neurosurgery at the Montreal Neurological Institute of McGill University, in a statement.

In the study, published in the journal eLife, Ruthazer and his colleagues applied synthetic cannabinoids to the eye tissue of tadpoles of the African clawed toad in one group, while the other group acted as a control. Researchers chose to observe tadpoles because like humans, their eyes also contain CB1 protein, which binds the psychoactive ingredient of marijuana (THC). They used microelectrodes to measure how retinal ganglion cells, whose fibers form the optic nerve, respond to light.

The tadpoles were then placed in a petri dish that was dotted with black marks on the outside shaped to look like the shadows of predators. Typically, tadpoles will avoid the dark as a defense mechanism to stay safe from predators.

Girl and smoke Smoking weed may help you see better in the dark, and act as treatment for degenerative eye diseases. Photo courtesy of Pexels, Public Domain

The findings revealed there was heightened activity in the presence of the cannabinoids in the retina. Meanwhile, when the lights were turned down, tadpoles given cannabinoids were more effective at avoiding fearsome marks than their sober counterparts. Researchers suspect the improved vision is linked to how the preoccupied CB1 receptors caused a decrease in the number of negatively charged chloride ions that traveled inside the neurons. This causes the membranes to become hyperpolarized, which leads to more electrical activity.

Although this gives some insight that marijuana could someday be used as a medical treatment to degenerative eye diseases, like retinitis pigmentosa, the results warrant further investigation, authors said.


In a similar 2004 study in the Jourrnal of Ethnopharmacology, researchers traveled to the Rif mountains in Morocco to observe the effects of marijuana on night vision. The researchers gave synthetic cannabinoid to one volunteer, and hashish to three more, and then measured the sensitivity of their night vision before and after. Marijuana improved night vision in all three participants. However, the study did not explore why vision improved.

The method hasn’t been tested on people yet, but it does provide hope for treatments for debilitating eye diseases like glaucoma, which causes blindness by killing off cells in the retina. Cannabinoids are actually known to have a neuroprotective effect on retinal cells.

Source: Miraucourt LS, Tsui J, Gobert D et al. Endocannabinoid signaling enhances visual responses through modulation of intracellular chloride levels in retinal ganglion cells. eLife. 2016.