Why Does Weed Make Your Eyes Red (and How to Get Rid of Red Eyes)

Weed red eyes

The redness of the sclera (also known as the white of the eye) is a completely non-dangerous side effect of cannabis consumption, so if you’ve found this article to check if you’re in any immediate danger do not fret, everything is quite alright.

On the other hand, if you want to get all the facts about “red-eye” stay tuned, as we’re going to cover all there is to know about this classic pot-lover giveaway.

Why do your eyes get red when you’re high?

Even though many people still believe that red eyes are caused by the smoke from a joint (or a blunt or a bong), this is completely untrue, because of no matter what type of consumption a person chooses, ranging from smoking, edibles, dabbing or vaping, the red eyes are gonna be there.

The reason behind the redness is actually THC.

One of the many ways that tetrahydrocannabinol affects us is by decreasing our blood pressure.

If you’re unfamiliar with how blood pressure works, I suggest you watch this awesome animation from TED Education, so you’ll understand the continuation of this post more easily.

One of the effects of decreased blood pressure is the expansion of our blood vessels (which include arteries, veins and capillaries).

In the case of our eyes, the ocular capillaries become dilated and take in more blood, and the expanded blood vessels on the surface of the sclera make the eyes appear redder in color.

Tetrahydrocannabinol (by reducing blood pressure), also reduces the intraocular pressure of the eye. Increased intraocular pressure is the key for all glaucoma diseases, and lowering the IOP (intraocular pressure), is the only way for us to battle glaucoma, which when left untreated can result in a severe loss of vision, and ultimately blindness.

One of the first studies conducted on this correlation showed that high THC strains can lower the IOP in the range of 25% to 30%. (1)

The main issue with treating glaucoma with marijuana is that the IOP needs to be constantly lowered in order for the eye to function properly (oral solutions such as oils, capsules and edibles are best for this because of their extended duration), while the second issue is that the users who constantly consume large quantities of THC can experience some side effects in their everyday life.

Tetrahydrocannabinol (THC) temporary decreases blood pressure in the entire body, which spreads our arteries, veins and capillaries. In the case of our eyes, capillaries expand to take in additional blood because of the lowered pressure.

The difference in people

If you and the people around you regularly consume cannabis, you probably already noticed that the same strain of weed has different effects on different people.

These differing effects happen because of a number of key factors which include genetics, sex, overall health and frequency of consumption (increased frequency causes cannabinoid tolerance).

You also might have noticed the same thing about the eyes. Some people get really intense bloodshot eyes, while on others the difference is barely visible, or even non-existent.

The redness is completely dependent on the person’s blood pressure. For instance, if you have high blood pressure, THC won’t be able to decrease it enough for your eyes to become super-red.

I actually have a completely opposite problem, as my blood pressure is rather low, so when I consume a potent THC strain, I literally look like the Terminator.

Besides the redness, when the session includes several joints/blunts I can also experience weakness in the legs and symptoms like feeling faint. This, of course, isn’t only a result of a low blood pressure but is brought about from a complex equation of factors I previously mentioned like age, sex, health, genetics etc.

Allergies can also play a factor in the overall “bloodshot volume”, as there are many people who are very sensitive to all smoke in general.

Another possibility for increased redness is cannabis allergy, but for users who have this unfortunate issue, red eyes are the least of their concerns. To find out more about this rare condition, click on the allergy link below.

We’ve now summed up the science behind the red eyes, so now I’ll be focusing on what we can do to diminish this telltale because sometimes we just don’t want everybody to know that we’re flying high.

If you have high blood pressure your eyes probably won’t change too much. On the other hand, if your blood pressure is low THC will most likely make your eyes appear really red in color.

How to get rid of red eyes after smoking weed

Red eyes

The most common way to alleviate your red eyes is, of course, various over-the-counter eye drops that are designed for eye allergies, redness and itchiness.

Pretty much all variations contain tetryzoline (also known as tetrahydrozoline), which is an alpha-agonist that causes dilated blood vessels to constrict.

As I previously mentioned, THC makes our blood vessels and capillaries to dilate (directly causing the redness), so the eye drops reverse this effect and return our eyes to a normal state.

These types of medications are generally quite safe for use, but I strongly recommend that you always carefully read the manual that comes with the drops.

There are a few alternatives to eye drops which can also constrict the blood vessels in our body, such as caffeine, chocolate, liquorice and sodium.

A common misconception is that increased hydration can be used for reducing the redness of the eyes, which is entirely false.

People frequently perceive the redness as a sign of dehydration, because they associate it with the accompanying sensation of dry mouth.

One of the many ways cannabis influences us is by activating the endocannabinoid receptors that are found in our salivary glands. Once excited by cannabinoids from weed, they slow down the fabrication of saliva, which causes us to feel like there’s a desert where our mouth used to be.

Over-the-counter eye drops for allergies constrict the blood vessels in the eyes, making them appear white again. Chocolate and caffeine are also capable of inducing these effects.


  1. Hepler RS, Frank IR. Marihuana smoking and intraocular pressure (letter). JAMA 1971;217:1392
About the author
Marco Medic

A passionate cannabis enthusiast, Marco mainly writes about the latest research on cannabis use in health.

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