The red-eyed stoner with a half-lidded gaze is an iconic trope of weed culture. And since there’s science behind this phenomenon, science can treat it, too.

The reason why people’s eyes get red when they’ve smoked, vaped, eaten, or drank some weed comes from vasodilation — in other words, cannabis causes the eye’s blood vessels to open up. The whites of our eyes, called the sclera, contain thousands of tiny blood vessels that we normally can’t see. But when some tokers hit the green, those whites become streaked with jagged cracks of red, which is just the blood vessels widening and filling up with more blood.

Vasodilation, while not great if you’re about to meet your partner’s parents, or if you’re about to show up to a job interview, is one of weed’s properties that is most sought out by seniors. By expanding the blood vessels in the eye, weed takes pressure off the peepers, which explains why a toke now and again can work wonders for treating glaucoma. (And why the DEA’s crappy weed farmer is now trying to cash in on his own patented cannabis eye drops.) 

There’s another reason why some folks get bloodshot eyes after getting ripped: allergies. Allergic reactions to weed are rare, but not unheard of, and they’re usually accompanied by breathing difficulties, coughing, exhaustion, and all the other symptoms of allergies. Furthermore, chances are that most people who respond this way to weed aren’t just allergic to cannabis; they’re allergic to all forms of smoke.

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Thanks, Bill Nye. Now, How Do I Get Rid of This Red-Eye Shit?

Unfortunately, if you’re one of those people who gets squinty-eyed after blazing, there’s not a whole lot you can do.

The simplest and quickest solution is to apply some eye drops. Look for ones specifically designed to treat redness or allergies

Another solution — and one we don’t recommend — is to cross-fade your sesh with some booze or tobacco. The nicotine in tobacco is a known vasoconstrictor, meaning it causes the blood vessels to narrow, effectively counteracting weed’s effect on the eyes. Small amounts of alcohol will open up blood vessels, but larger amounts of booze — as in more than enough to get you shit-faced — will constrict the blood vessels instead. 

Due to alcohol and tobacco’s seriously negative health effects, it’s not a good idea to mix either of these with your weed. But if you’re already out partying harder than a frat boy after finals, well, just know that you may not end up with demon-red eyes by the end of the night. (You may, however, end up with a toilet full of vomit and a head full of regrets.)

Drinking water can help reduce your red-eye situation, too, because hydrating helps everything. Often, when cottonmouth sets in, our body becomes a bit dehydrated, which can create the sensation of dry skin and extra dry-eyes. Similar to the way eye drops treat dry, red eyes, drinking a lot of water can help regulate eye moisture. But, just know that H2O won’t bleach the redness out of your eyes or help you hold your eyelids open.

All in all, you may not be able to do much about redness in your eyes after consuming cannabis. If that’s the case, just try to plan your seshes so you aren’t doing anything critical while lifted, like meeting a probation officer or showing up to a live TV interview

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