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The Science Behind Marijuana Use & Red Eyes in Ohio

the science behind marijuana use & red eyes in ohio

Most people who use cannabis are familiar with the glossy stare, dilation, and redness it can cause to the eyes. Commonly thought to be caused by smoke from the burning plant, there is more behind the tell-tale red eyes than just irritation from smoke.

Marijuana red eyes occur for the same reason people experience dizziness – vasodilation. It is one of the common physical effects that cannabis can cause. In this article, we explain what causes vasodilation and possible ways to remedy it.

Medical Marijuana Effects on Heart and Blood Vessels

When tested on animals, THC lowers blood pressure, yet humans experience the opposite effect. For those who are novice users, the effect is increased blood pressure for a temporary period of time. It can vary depending on the potency and type of cannabis, but on average, the short-term increase in blood pressure lasts less than an hour.

After repeated consumption, blood pressure decreases gradually and may return to normal. That is because THC relaxes the smooth muscle of the arteries, causing them to relax and increase their diameter. This impact on blood vessels and capillaries is known as vasodilation.

As blood flow is restricted, an increase in heart rate is triggered to compensate for the decreased blood pressure. In turn, the eyes become red because the blood vessels in the sclera (white of the eye) are dilated.

Another explanation is that THC, one of many cannabinoids found in cannabis, interacts with cannabinoid receptors that are part of the endocannabinoid system of the body. The receptors are found throughout the body, most notably in the eyes.

For this reason, eye redness may occur regardless of how cannabis is consumed, be it smoking, vaping, or eating. Impacts on the cardiac system can be significant as the heart rate can increase as much as sixty percent over the normal resting rate.

Another symptom commonly seen in users after they have consumed high doses of THC is called postural hypotension. The lower blood pressure may temporarily cause dizziness or fainting.

Is Everyone Affected?

red eyes

Some patients will experience red or bloodshot eyes every time they use cannabis. For others who are less sensitive, the symptom may show at times and not at others, depending on their genetics and the dosage and quality of the product they consume.

It is easy to tell the difference between eye redness caused by cannabinoids from eye redness caused by an allergy. A person who is allergic to cannabis will usually also experience symptoms such as dry skin, hives, itchiness, runny nose, sore throat, or nasal congestion.

Those who are allergic to the smoke from cannabis generally also experience the same effect after having been exposed to the smoke from tobacco or even incense.

How Can I Prevent Red Eyes from Happening?

What should you do if you are looking to get rid of red eyes from cannabis? There are two things that may work:

1. Eye Drops

Using eye drops is the most common and practical way to prevent red eyes from occurring. Along with providing lubrication for the eyes, they contain chemicals like tetrahydrozoline hydrochloride and potassium chloride. These chemical compounds help restrict the blood vessels in the eye, reduce intraocular pressure, and make them less noticeable.

2. Using Strains High in CBD

Another way to mitigate red eye is to choose cannabis strains with a higher CBD content and a lower THC content. This is because CBD does not cause vasodilation.

How THC Benefits the Eyes

eye drops

As mentioned, the endocannabinoid system is a cellular communication network that interacts with the cannabinoids found in cannabis. The human eye contains very high levels of cannabinoid receptors, namely the CB1, which are used by the brain to process vision.

A 2016 study on primates published in Neural Plasticity found that cannabinoids can be manipulated to change how electroretinographic waves interact with the retina. To come to this conclusion, researchers used an electroretinogram to measure the effects of light on the eyes.

They found cannabis receptors were responsible for managing how the eyes respond to light. While findings require more research, this study provides promise for the potential for cannabis as a treatment for many eye diseases, such as glaucoma, intraocular pressure, neurodegenerative blindness, and diabetic retinopathy. This is why you see glaucoma and related eye disorders as eligible conditions for medical marijuana use.

Another benefit cannabis brings to the eyes is enhanced night vision. As cannabis engages cannabinoid receptors in the eyes, vision becomes more apparent in lower lighting conditions. Researchers have studied this aspect of cannabis for decades.

Make DocMJ Your Cannabis Healthcare Provider


Our friendly physicians provide the medical cannabis health check required to apply for a medical card. If you have questions about medical marijuana side effects, you can discuss them with our expert providers.

DocMJ also provides support and education for patients so they can make an informed choice about smoking cannabis or using other medical cannabis routes.



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