Cannabis Science

Does Weed Dilate Pupils?

pupil with a blue iris

It’s no secret that weed can affect your eyes in various ways. Many people notice their pupils are bigger when they’re stoned but is it all in their head? Does weed dilate pupils? Or will your pupils constrict after you hit your mushroom bong? Here’s what we know. 

Photo: Unsplash 

Does Weed Dilate Your Pupils?

Yes! Weed can dilate your pupils. If you never noticed this change before, look at your eyes before you fire up your bong and then after. 

Just to catch you up, your pupils are the black holes in the center of your eye. The colored area around it is the iris. The iris is responsible for making your pupils bigger or smaller typically depending on the amount of light in your environment. 

However, besides light, there are other reasons your pupils may dilate or constrict, such as using certain substances. 

Vice says, “After taking cocaine, marijuana, or amphetamines, for example, your pupils get noticeably larger (Mydriasis).”

But why?

Vice says the same chemicals in substances that make you feel happy or energized are the same chemicals that make your pupils dilated. 

And while N Vision Centers did not mention weed, they said stimulants, hallucinogens, and psychedelics can activate the muscles that dilate pupils.  

We know that THC is the main reason why your eyes can go red during a smoke sesh but is that the reason why your pupils dilate? Possibly, but we don’t know for sure. 

While your pupils dilating is not typically a cause for concern, in some rare cases it can be. 

According to Pop Magazine, “More rarely, the pupil dilation provoked by cannabis can create dazzlements and imbalances between near vision and far vision.”

In addition to that, Pop Magazine mentioned that stoners with multifocal contact lenses can have a decrease in their peripheral vision after having a blunt. 

In addition to the effects we mentioned previously, Pop Magazine says weed can result in the following:

  • Slowing down of image processing by the retina
  • Red eyes
  • Eye fatigue
  • Disruption in spatial perception
  • Ocular dryness and 
  • Meibomian gland dysfunction 

When Will My Eyes Go Back to Normal?

Don’t worry, the changes in your eyes are temporary. 

Very Well Health says that the time it takes for your pupils to go back to normal depends on the substance, dose, and your body’s ability to break down and remove it from your system. 

If you notice strange eye changes when you haven’t used weed, then we’d recommend seeing a doctor. However, remember, pupils change their size for a variety of reasons outside light and substances. Your pupils can also change size temporarily if you’re attracted to someone or when you’re anxious. 

What If Weed Doesn’t Dilate My Pupils?

There is a chance that your pupils won’t dilate if you smoke weed and that’s perfectly normal. 

Remember, weed affects everyone differently and so everyone won’t experience all of the same effects.

Not everybody agrees that weed dilates or constricts your pupils anyway. 

Los Angeles DUI Attorneys say, “No, smoking marijuana will not dilate the pupils of your eyes. This is one key difference between drivers who are drunk and who are high from cannabis.”

Some stoners may find that their pupils constrict on weed!

As a matter of fact, a 1977 study found that weed did the opposite of pupil dilation. The study stated, “In an experiment using ten subjects, marijuana produced a dose-related constriction of the pupil at low photopic light levels.”

A more recent study in 2020 found similar results. The study said, “acute cannabis administration may cause pupil constriction, and conjunctival injection (red eye), self-limiting effects, which do no require any particular treatment.”

Finally, you may find that only one pupil is dilated or constricted and not the other. That’s normal too, according to Very Well Health. 

Is Pupil Dilation or Constriction Dangerous? 

As the 2020 study said, pupil constriction and red eyes associated with cannabis use, do not require any particular treatment. 

However, there may be some problems associated with continuous pupil dilation. According to N Vision Centers, “The continuous dilation of the pupils can cause long-term vision problems.”

While they didn’t mention weed specifically, they mentioned alcohol can have long-term effects on your eyes. The article mentioned dry eye syndrome and substance-induced glaucoma in people who drink. 

There is no evidence that this is the case with weed users. As a matter of fact, scientists are researching weed as a treatment for glaucoma but there are still conflicting conclusions on that. 

At the same time, dilated pupils can be mildly uncomfortable. N Vision Centers say, “People who have dilated pupils will be more sensitive to sunlight (or bright lights in general), since their pupils cannot constrict to protect the eyes from exposure to too much light.”

The solution to this is simply to put on good sunglasses. 


Does weed dilate pupils? Yes. Stoners have also reported constricted pupils too. Weed simply affects everyone differently which would explain why some stoners have dilated pupils while others don’t. The changes to your pupils when you’re stoned are not considered dangerous and are temporary. However, there is slight concern with long-term pupil dilation but we don’t have much information on how this affects stoners. So in the meantime, you can throw on your favorite sunglasses and relax.


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].