How Long Do Red Eyes Last From Weed?
Article written by
Dipak HemrajHead of Research and Education
Content reviewed by
Dr. Lewis Jassey
Whether you’ve been consuming marijuana for a week or a decade, odds are you’ve looked in the mirror and wondered, “Why are my eyes bloodshot?”
Of course, every cannabis user’s experience with the plant is unique, but red eyes are often the most telling sign that someone has ingested cannabis. Red eyes from cannabis use tend to last one to two hours and may last up to three or four hours for some people.
Some people experience it every time they use marijuana, and others may only experience it occasionally. This can be due to differences in body chemistry and the differences between cannabis strains.
However, red eyes are rarely ever anything serious to worry about.
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Causes of Red Eyes From Cannabis Use
Without getting too deep into the science, it all comes down to blood pressure and blood vessels.
One of the main active components in cannabis is tetrahydrocannabinol (THC). When cannabis is ingested, this compound enters the bloodstream and interacts with the body’s endocannabinoid system (ECS). The ECS contains receptors spread throughout the body, which cannabinoids like THC bind to. These receptors are referred to as CB1 and CB2 receptors.
The red-eye effect is caused by THC molecules binding to CB1 receptors in the brain and eyes. That binding induces vasodilation in the eye’s blood vessels, causing an increase in blood flow and a decrease in blood pressure. As blood pressure begins to lower, blood vessels begin to dilate. This phenomenon happens all over the body but is most visible in the ocular capillaries.
Smoking cannabis has been reported to decrease intraocular pressure, aka pressure in the eye, by up to 30%. This decrease in intraocular pressure is why cannabis can be used to help with eye conditions such as glaucoma.
Glaucoma is a class of eye diseases that impacts the optic nerve and can lead to blindness. It’s often caused by high intraocular pressure (IOP). So, while the increased blood flow to your ocular capillaries is what causes red eyes, it’s also the sensation that causes relief for glaucoma patients who use medical marijuana.
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Does the Ingestion Method Matter?
There are many different methods of cannabis ingestion. Common methods include smoking, vaping, and oral administration, such as edibles. Red eyes from cannabis use are directly linked to the THC concentration in cannabis. This means that regardless of the method of ingestion, THC molecules from cannabis will enter the bloodstream and bind to CB1 receptors in the eye.
Because the appearance of red eyes after ingesting cannabis is directly linked to THC, cannabis strains high in THC are more likely to cause red eyes than those low in THC.
The main difference between ingestion methods is the time it takes to appear. Ingestion by smoking or vaping tends to result in red eyes quickly, as the THC moves directly into the bloodstream and rapidly enters the blood vessels in the brain and eyes.
Irritation caused by smoke may also cause eyes to red, but this is not a significant factor. Ingestion via edibles may result in a slower onset of red eyes, as the THC must pass through the liver before entering the bloodstream.
When Will the Eye Redness Go Away?
Typically, red eyes caused by cannabis ingestion will go away one to two hours after onset. However, this will differ based on how quickly your body metabolizes THC and the concentration of THC in the particular cannabis strain injected. The more THC in the strain, the longer red eyes can last. Red eyes due to marijuana can last three to four hours for some people.
Do Other Cannabinoids Effect Eye Redness?
The eye-reddening effects of cannabis are tied directly to THC consumption. THC causes increased blood pressure and heart rate and the subsequent expansion of ocular blood vessels. In practical terms, that means that the more THC you consume, the redder your eyes will become.
As users build a tolerance to THC, however, they may notice a significant decrease in eye redness. In the same way that frequent cannabis consumption will eventually decrease the strength of intoxication, regular pot users experience less fluctuation in blood pressure and heart rate and, in turn, lower levels of capillary dilation.
Likewise, cannabis users who prefer CBD, CBG, or CBN-dominant strains will experience significantly less eye redness than THC consumers. Unlike the immediate rush of THC, CBD, CBG, and CBN have far less psychoactive effects and can even decrease blood pressure, eliminating the cardiovascular reaction and eventual red eyes of traditional, full-strength THC cannabis.
How To Get Rid of Red Eyes From Marijuana
Now that we know the science behind how and why our eyes turn red after consuming cannabis, let’s break down how to eliminate the pesky pot side effect. Fortunately, there are a few effective options for masking red eyes.
Over-the-Counter Eye Drops
Over-the-counter (OTC) eye drops designed for allergy treatment are the most common method to reduce red eyes caused by marijuana. Eye drops used to treat allergic reactions contain a molecule called tetryzoline (tetrahydrozoline). Tetryzoline is a vasoconstrictor; it constricts the dilated blood vessels in the eye. Constricting the blood vessels causes a reduction in blood flow, lessening the appearance of red eyes.
Caffeine
Caffeine may reduce eye redness by a similar mechanism to eye drops. Caffeine causes vasoconstriction, reducing blood flow in the eyes and decreasing redness. Consuming one of the following beverages will help reduce eye redness.
- Coffee
- Energy drinks
- Cola
- Tea
Cold Compress
Coldness causes the blood vessels in the peripheral body parts (like the eyes) to constrict, reducing blood flow in these areas. This is a survival tactic the body naturally undergoes when cold to send most of the blood to vital organs such as the brain and the heart. This is why people often experience pale or blue fingers and toes when cold.
Try placing a cold compress over your eyes or splashing some cold water on your face to reduce red eyes. Alternatively, you could take a cold shower or jump in an ice bath if you are brave.
Wear Sunglasses
If you cannot reduce the redness in your eyes, you could wear sunglasses. This will not make the redness disappear, but the sunglasses will hide it. Unfortunately, this is not a good solution for the winter.
Use a Low-THC Cannabis Strain
Using a low-THC strain of cannabis will not reduce already red eyes; however, it may prevent the onset of red eyes. As vasodilation in the eyes is directly linked to THC concentration in cannabis, ingesting a cannabis strain that is low in THC will reduce the chances of red eyes occurring.
The Bottom Line
Cannabis causes red eyes due to THC’s impact on blood pressure and heart rate, leading to ocular blood vessel dilation. Different cannabinoids affect redness levels, with THC being the main culprit. Possible remedies include eye drops and hydration.
So next time you wonder why your eyes are red and look bloodshot, remember that it’s just part of the cannabis experience, it’s temporary, and it’s nothing to be concerned about.
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Originally Published: April 2022
Last Updated: March 2024
