Why Does Weed Make Your Eyes Red

Stop a random person on the street and ask them how they can identify someone who has taken the weed, and many of them will point out bloodshot eyes as the first thing.

But what many people do not know is how this redness comes about. This is what I want to explain in a nutshell.

If you have experienced this symptom and gotten scared by it, relax, it’s not that big of a deal. And you should know that you can still experience this symptom whether you smoke or ingest the weed.

A bit of anatomy and physiology

When THC hits your bloodstream, it triggers some cardiotropic effects. This results in increased blood pressure and blood supply to different parts of the body.

The white of the eye is highly vascularized. These capillaries dilate when there is a surge of tetrahydrocannabinol (THC) in the body.

This process is known as vasodilation. When this happens, more blood can flow into those capillaries and supply blood to the eye. So, in short, the redness you see in your eyes after having a blunt is because of the increased blood supply to the eyes. Not a bad thing at all.

This also explains why cannabis is sometimes used in the treatment of glaucoma.

The more potent the weed, the sooner your eyes will become red and the greater the intensity of redness you will experience.

Some low strains THC may not give you significant redness. It also depends on how accustomed you are to taking weed. New stoners may exaggerate this symptom as their bodies react more to the effects of THC.

Myths on bloodshot marijuana eyes

It is also important to highlight that the redness has nothing to do with the act of smoking. So long as you are ingesting THC, expect to get bloodshot eyes sooner or later.

Some people also believe that red eyes are caused by an allergy to the weed. This is hardly ever the case, and so taking antihistamines prior may not be a solution.

Is there anything to worry about?

Other than the lack of appeal, there is no negative effect associated with marijuana bloodshot eyes.

You may also be concerned about some people finding out what you have been up to.

Other than this, there isn’t much else to be worried about.

How to avoid red eyes

There is little you can do to avoid getting red-eyed. One of the few things you can consider is to go slow on high THC strains.

Strains that are high in CBD and CBN may give you similar therapeutic value without having to let out that you have been toking. Alternatively, you can try using eye drops to clear out the red in your eyes.

You could also try some tricks that help in flushing THC out of your system, such as exercising and using detoxifiers.

Other than that, you can wait it out. As we said earlier, the red eyes mean more blood supply to your eyes, which never quite harmed anyone.

So the next time someone is concerned about your bloodshot eyes after toking, proudly explain the physiology behind it to them. You could also educate them on how this can be used in the treatment of glaucoma.


  1. NCBI: Marijuana and Glaucoma. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK224386/
  2. McGill (2018): It’s not the smoke from a joint that makes your eyes red. Retrieved from https://www.mcgill.ca/oss/article/did-you-know/its-not-smoke-joint-makes-your-eyes-red
  3. Harvard (2018): Marijuana linked to high blood pressure risk. Retrieved from https://www.health.harvard.edu/heart-health/marijuana-linked-to-high-blood-pressure-risk