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Why Does Marijuana Make Your Eyes Red?

Marijuana dilates blood vessels in the eyes, making them appear red after smoking.

Have you ever noticed a person with red eyes who can’t seem to stop smiling? Chances are, they might have used marijuana recently.

Red eyes are one of the few reliable physical indicators that suggest a person is high.

But why exactly does marijuana cause redness in the eyes, and can you do anything to make it go away?

Let’s take a look at why marijuana causes red eyes.

The Science Behind Marijuana and Red Eyes

The Science Behind Marijuana and Red Eyes
(Photo: Shutterstock)

Marijuana is definitely known for making your eyes red, but not everybody who uses marijuana gets red eyes.

This is largely due to genetic differences in individuals, making some more susceptible to developing red eyes than others.

However, due to the stigma that still surrounds marijuana in many places, having red eyes can be problematic.


Marijuana typically makes people’s eyes red because it causes changes to the blood vessels in the eye.

The sclera, or white area of the eye, contains many small blood vessels. These blood vessels usually go unnoticed under normal circumstances.

But when someone smokes, eats or vaporizes marijuana, the blood vessels in the eye can become enlarged. This characteristic is known as vasodilation.

When the blood vessels expand, they become more noticeable, giving the eyes a reddish appearance which contrasts significantly against the whiteness of the sclera.


For a very small percentage of marijuana users, red eyes can be the result of an allergy. Like all plants, marijuana produces chemicals that interact with the immune system.

While these interactions are sometimes beneficial, some people have immune systems that can react negatively to marijuana.

An allergy to marijuana is easy to distinguish from typical red eye symptoms. Allergies to marijuana will often be accompanied by other symptoms like itchiness, hives, dry skin, runny nose, nasal congestion, or a sore throat.


Marijuana contains over 113 different cannabinoids other than just THC. Most of the cannabinoids in marijuana do not contribute to the red eye effect.

THC is believed to be the primary cause of red eyes, while other less abundant compounds like CBD have not been found to have this effect.

This is because CBD and other cannabinoids do not have the same vasodilating properties as THC.

How to Prevent and Hide Red Eyes

How to Prevent and Hide Red Eyes
(Photo: Shutterstock)

Eye Drops

The most common method of preventing red eyes is to use eye drops like Visine.

These drops act to lubricate the eye, and also introduce chemicals like potassium chloride and tetrahydrozoline hydrochloride.

These compounds cause vasoconstriction, which causes the expanded blood vessels in the eye to become smaller and less noticeable.

Eye drops are generally considered the most practical approach to treating red eyes from marijuana use, particularly for medical patients who require high doses of THC.

High CBD Strains

Another option to alleviate red eyes from marijuana is to use strains of marijuana that have a higher CBD content. Strains that have more CBD tend to have less THC, and vice-versa.

Because CBD does not contribute to vasodilation, the vasodilating effects of THC tend to be reduced in high CBD strains.

The end result is that strains that are higher in CBD will tend to produce less red eyes.


You may have noticed that red eyes are less common in regular users of marijuana.

This is because these individuals have built up a tolerance to the vasodilating effects of THC through repeated use.

While this may not be a practical method for many people, it is one way to mitigate the effect of redness in the eyes.

The Bottom Line

Marijuana with high levels of THC can cause red eyes because it expands the blood vessels in the eye.

This effect can be limited by using eye drop products like Visine, which contain chemicals to make those blood vessels smaller.

Red eyes can also be avoided by using marijuana strains with lower THC content and higher content of other cannabinoids like CBD.