Cannabis Science, CBD

Why Does Weed Make your Eyes Red?

Why does smoking weed make your eyes red

For most people, weed leads to feeling high, getting the munchies and having bloodshot red eyes. Many people who consume cannabis in any form get red eyes, not just from smoking as it generally thought. We’ve already answered why weed gives you the munchies but why does weed make your eyes red? Let’s see what science says about stoned eyes.

Photo: Unsplash/Unsplash (mashup)

Why Does Weed Make your Eyes Red?

The reason weed makes your eyes red is because of the cannabinoids it has. Cannabinoids, to put it simply, are a group of substances found in the cannabis plant. While there are over a hundred, we tend to focus on tetrahydrocannabinol (THC) and cannabidiol (CBD). Cannabinoids interact with the cannabinoid receptors that are a part of the endocannabinoid system. When they interact with the receptors, they cause the munchies, being high and yes, red eyes. 

According to an article by McGill University, cannabinoids cause red eyes because of vasodilation. Vasodilation refers to the dilation of blood vessels which leads to a decrease in blood pressure. The article says, “The increased blood flow to your eyeball causes the red appearance”. THC is said to be the cannabinoid responsible for that. 

Vasodilation is also the reason behind why some people feeling dizzy after using cannabis. 

How to Deal with Red Eyes

While red eyes aren’t dangerous, we don’t necessarily want to be walking around with bloodshot eyes. 

Ohio Marijuana Card gave some great tips to deal with and avoid red eyes. 

  • Use a different strain- Their article mentioned that strains higher in THC are linked with red eyes so opt for strains that are higher in CBD and CBN.
  • Try eye drops- There are eye drops on the market that will fix red eyes and get your eyes back to normal. These will super handy if you got stoned but didn’t want to announce it to the whole world. We recommend using eye drops just before you partake to avoid having stoned eyes.

Other suggestions include wearing a pair of sunglasses to hide your red eyes, or simply just letting time pass. Your eyes will return to their regular hue in a little while. If you’re super concerned about people judging you, time your sessions in a way that gives you sufficient time for your red eyes to clear. 

Is Having Red Eyes Dangerous?

Well, most sources say there is no real danger in your eyes turning red. It’s more about the dizziness. Since vasodilation is the same reason people may feel dizzy, be on the lookout for that. If you’re feeling dizzy, drink plenty of fluids and get some rest. 

However, the American Academy of Ophthalmology disagrees about the safety of marijuana and eye health. According to an article posted on their website, marijuana use can damage the optic nerve. The article says, “The optic nerve can also be damaged by low blood flow”. It stated that marijuana may contribute to low blood flow.

Weed and Glaucoma 

There are conflicting views about the role of weed in treating glaucoma. According to the Glaucoma Research Foundation, glaucoma is “a disease of the optic nerve, the cable that carries visual information from the eye to the brain”. Glaucoma can therefore result in vision loss and blindness. Treatment for glaucoma typically involves lowering the pressure in the eye. 

Is Weed Good for Glaucoma?

It has been posited that since weed can lower the pressure in the eye then it should be a viable solution. According to a study done on mice, scientists have found a way that THC could provide some advantage. 

However, as the American Academy of Ophthalmology said in their article, using marijuana for glaucoma isn’t practical. According to the article in order to maintain the desired eye pressure, you’d have to use quite a bit of weed on a daily basis. It said, “ingest about 18 to 20 mg of THC six to eight times a day, every day.” If that’s in fact true then you can see why marijuana may not be seen as a viable solution. That would require someone to spend quite a bit of money, avoid operating machinery and not be productive at work.

As said before, it’s believed that weed can damage the optic nerve. The Glaucoma Research Foundation, says, “Lower blood pressure could result in reduced blood supply to the optic nerve, which in turn might harm the optic nerve”. The American Academy of Ophthalmology and other organizations, therefore, don’t recommend weed as a treatment for glaucoma. 

The Role of CBD in Glaucoma Treatment

The aforementioned study done on mice said that CBD may actually interfere with the positive effects of THC on the eyes. According to Science Daily, while THC lowers the pressure in the eye, CBD actually increases eye pressure. An increase in eye pressure would make glaucoma worse. Science Daily says, “The study, which was conducted in mice, specifically found that CBD caused an increase in pressure inside the eye of 18 percent for at least four hours after use.”

Conclusion on Stoned Eyes

The reason why weed makes your eyes red is that the cannabinoids cause vasodilation. When the blood vessels dilate, more blood goes to the eye and so it appears red. You can treat it at home with eye drops or opt for weed with less THC and more CBD. Weed is being looked at as a treatment for glaucoma since the vasodilation that causes red eyes also lowers eye pressure. Interestingly, THC decreases eye pressure but CBD can actually increase eye pressure which could make glaucoma worse. Weed can also decrease blood pressure which can damage the optic nerve. That said, there has to be more research here to find out how to yield the positive benefits and avoid the negative outcomes.


About Trevann

Trevann is Stoner Rotation’s Jamaica-based lead writer for the Science section of our cannabis blog. She graduated with honors receiving her Bachelor of Science degree in Molecular Biology from the University of West Indies, Mona. For the last three years, she has covered some of the biggest questions around cannabis and health underpinned with research from supporting studies, medical journals and scholarly articles. Got something on your mind? You can reach her at [email protected].