It’s a common misconception that red eyes and a glazed stare of someone who’s high on marijuana are due to irritation from smoke. But we now know that the cannabinoid THC is the key culprit.
The tell-tale red eyes of someone who’s high on marijuana are often blamed on smoke irritation. But, that’s a common misconception. Marijuana makes your eyes red for the same reason it’s used to treat glaucoma— a physiological mechanism known as vasodilation.
The vasodilation behind your red eyes is triggered by the main psychoactive ingredient tetrahydrocannabinol (THC). THC is just one of 113+ active compounds in marijuana, known as cannabinoids. These cannabinoids interact with cannabinoid receptors throughout your body, and in particular, your eyes.
When THC binds to cannabinoid receptors, it lowers our blood pressure, which in turn causes the dilation or expansion of blood vessels and capillaries. In the case of your eyes, the ocular capillaries dilate, causing an influx of blood flow to the area, creating a red appearance of the sclera (aka the white of the eyes). That’s why we call it “bloodshot” eyes.
If you’ve ever wondered “do edibles make your eyes red too,” this explanation should provide some clarity. As edibles, just like topicals and tinctures, can also contain THC, they too have the potential to cause red eyes through vasodilation.
For glaucoma patients, the THC induced vasodilation of ocular capillaries also temporarily reduces intraocular pressure. High intraocular pressure is the main symptom of glaucoma and can contribute to optic nerve damage and vision loss. Therefore, reducing this pressure is a key priority of glaucoma treatment. One study, published in the Journal of the American Medical Association, reported that smoking marijuana reduced intraocular eye pressure by up to 30%.
While red eyes are a dead giveaway that someone has been smoking marijuana, it’s not always a guaranteed symptom. That’s because each strain of marijuana has a different concentration of THC. Hence, someone may experience intensely red eyes after ingesting a high THC strain, but barely notice the difference after a low THC strain.
However, there’s more at play than just THC content. As you may have experienced yourself, the same cannabis strain can have different effects on different people. These varying effects are due to a number of individual factors, including gender, genetics, and overall health.
Whether a person experiences red eyes or not is primarily influenced by their blood pressure. For instance, people with high blood pressure need more THC to lower their blood pressure enough to cause intense bloodshot eyes. Although, those with naturally low blood pressure can quite easily experience terminator red eyes.
With that being said, people with allergies to marijuana or smoke, in general, can experience exacerbated symptoms. But for users with an allergy, typically, red eyes are the least of their concerns.
Red eyes are a completely harmless side effect of marijuana and usually aren’t a problem. But, they can be a nuisance, especially for those who need to medicate with cannabis to get throughout the day. Due to the persistent stigma surrounding marijuana, attending work or university with bloodshot eyes can trigger unwanted attention and potential legal questioning. Fortunately, there are some strategies to reduce the severity of redeyes after using marijuana.
Over-the-counter eye drops designed to treat allergies, redness, and itching are the most effective way to alleviate red eyes. Basically, all variations of eye drops contain tetryzoline, which is an alpha-agonist that constricts blood vessels. Essentially, this reverses the dilation caused by THC, which then reduces blood flow to the eyes and the accompanying redness.
Other items you might have lying around the house can also trigger vasoconstriction. For instance, stimulants such as caffeine can help induce vasoconstriction. Therefore, drinking a fresh cup of coffee or enjoying a few squares of dark chocolate might help alleviate red eyes.
Cold water is also a strong vasoconstrictor. It forces the body to send blood toward our core to protect vital organs as part of a survival instinct. Splashing cold water on your face or placing an ice pack across your eyes can achieve this effect. If you’re brave enough, a cold shower or ice bath will also do the trick.
The redness will eventually subside and return to normal. Therefore, you can be patient and simply wait for THC to run through your system. The key question is, however, how long do your eyes stay red after smoking marijuana?
Unfortunately, the answer isn’t clear cut. You may have to wait from 2 to 12 hours, depending on a variety of factors, including the administration route and the dose of THC. For instance, when marijuana is smoked or vaporized, THC is rapidly absorbed into the bloodstream. Effects are felt within 2-5 minutes, peak within 15 to 30 minutes, and usually subside within one to three hours, depending on the dose.
Edible THC, on the other hand, is much slower and longer-lasting. It takes effect within 30 to 90 minutes, reaches maximum effect after two to three hours, and can last for four to 12 hours, depending on the dose. Individual factors, including your tolerance, body weight, and metabolism, also impact the pharmacokinetics of marijuana and will determine how long it will take for your eyes to return to normal.
We’ve covered several ways to treat red eyes, but can this side effect be prevented from occurring in the first place?
Since THC is the main cannabinoid responsible for red eyes, opting for a low THC strain or using CBD only will minimize the unwanted side effect. Of course, you won’t experience the same psychoactive effects, although high-CBD strains are ideal for days you don’t want red eyes.
You may have read that staying hydrated can minimize the redness, but this is entirely false. The next best form of prevention is planning and time management. If you need to use marijuana before work or an important meeting, plan to do so well in advance to allow your body and eyes time to recover.