High eyes are the hallmark sign of cannabis intoxication. Whether you smoke, vape, or eat cannabis, it is likely that soon after, the whites of your eyes will become red.   Red eyes can be an inconvenient side effect of using pot. They are a bright, shining signal that you’re stoned.

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The Impact of THC on the Eyes

THC causes red “high eyes” because it is a vasodilator. Among their many effects, cannabinoids cause hypotension. Hypotension is low blood pressure. According to a 2005 Handbook of Experimental Pharmacology article, initial cannabis use can cause hypertension, but repeated cannabis use causes the smooth muscle of the arteries to relax and increase in diameter. Since 1971, researchers have been aware that cannabis inhalation can regulate intraocular pressure (IOP). IOP refers to the buildup and flow of fluid in the eye. Researchers have assumed that cannabis’s effect of reducing IOP is a response to THC interactions with CB1 receptors. These receptors are located in the brain and eye and seem likely to be involved in the process of regulated IOP. A 2018 Investigative Ophthalmology & Visual Science study found that THC reduced IOP through CB1 and GPR18, molecular pathways that belong to the endocannabinoid system.  Although the connection between cannabis and red eyes has often been seen as a comedic inconvenience, it turns out that high eyes are a sign that the THC is active in your system. 

Does Everyone Get Red Eyes?

Not everyone is impacted by THC in the same way. While some cannabis consumers will get red eyes every time they use pot, some will not. The severity of the symptoms depends on the individual and cannabinoid content as well. Cannabis that contains higher levels of THC are most likely to cause corneal vasodilation because THC reduces blood pressure throughout the body, including in the eyes.  Red eyes are almost never caused by cannabis smoke itself. A person with a cannabis allergy or a sensitivity to smoke may experience eye redness and itchiness, but typically, red eyes are a symptom of vasodilation caused by THC. If allergies are the culprit, other symptoms such as hives, sore throat, runny nose, and itchy skin will follow. 

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Should You Be Worried About Red Eyes?

Red eyes are high eyes. If you’re trying to hide your cannabis use, red eyes won’t help. Corneal vasodilation is a telltale sign that you are high. Although cannabis is legal in most states for medicinal use and in a growing number of states for recreational use, there are still people who will be offended by cannabis consumption. Put simply, if you’re going to get high, be prepared for red eyes and smoke with people you trust… or be that person wearing sunglasses indoors.  Red eyes don’t cause heart problems, but they are a reminder that cannabis has an impact on cardiovascular health.  As we discussed in our doctor-reviewed article could affect your heart, but the science is inconclusive.  about cannabis and heart health, if you have a heart condition, abusing pot could affect could come with certain cardiovascular risks. If you have a heart condition or are worried about cannabis' effect on your heart, please consult your doctor. 

How to Avoid or Get Rid of Red Eyes

If you don’t want high eyes to give you away or your eyes are already red and you’d like to change that, there are a few ways to mitigate the severity of the symptom.  Reduce your THC consumption. THC is responsible for vasodilation. The more THC, the more likely it is that your body will experience this effect. That means that there is a greater likelihood of corneal vasodilation, or red eye, if you consume a lot of THC.  Use eye drops. Choose eye drops that are designed to reduce eye redness. Use one drop in each eye, and the redness should reduce slightly.  Wear sunglasses. If all else fails, cover your eyes. If you’re going to be indoors, this is probably going to cause more suspicion than it eliminates. Stick to this strategy only if you plan to be somewhere that sunglass-wearing is appropriate.  

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