Why Do My Eyes Go Red After Consuming Cannabis?

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One of the most obvious and telling signs that you’ve just consumed cannabis is red, bloodshot eyes. In fact, it’s almost like a guaranteed side effect. Use some and you’re sure to develop red, bloodshot eyes. But why does this happen? How do you get rid of it? More importantly, is it dangerous? Before we go into details though, let’s take a quick look at the anatomy of the eye and how it functions.

The Anatomy of the Eye

The eye is made up of various parts:

  • Sclera – the smooth and white surface of the eye.
  • Conjunctiva – the clear membrane that covers the sclera and lubricates the eye by producing tears and mucus.
  • Iris – the colored portion of the eye which connects to the eye muscle that contracts and dilates the pupil.
  • Lens – the transparent membrane that’s located behind the pupil. It refracts light and helps the eye focus on objects.
  • Pupil – the black center of the iris that regulates the amount of light that goes into the eye.
  • Cornea – the clear membrane that covers the iris and pupil. It refracts light so you can focus clearly on objects.
  • Retina- the membrane that covers the back of the eye. It interprets the objects you see and transforms them into signals that travel to the brain.
  • Optic nerve – the nerve that transmits signals from the eye to the portion of the brain responsible for vision.
  • Anterior and posterior chambers – the structures that maintain and regulate aqueous humor.
  • Aqueous humor – the fluid that provides eye nutrition and eye pressure.

For these eye parts to function properly, it receives oxygenated blood supply from the branches of the ophthalmic artery. These arteries also carry the nutrients the eye needs.

The blood also travels into the capillaries that drain into the ophthalmic veins. The veins, in turn, carry the unoxygenated blood back to the lungs for oxygenation.

Why do your eyes get red when you’re high?

Tetrahydrocannabinol or THC, the most abundant cannabinoid in cannabis, has an effect on the eye’s arteries. Studies have shown that THC consumption dilates or widens the arteries and capillaries found in the eye. Because these are dilated, there will be an influx of blood into the eyes, especially to the sclera.

This increased blood supply, in turn, causes the sclera to turn redder in appearance. This THC effect is the main reason why you develop red eyes after consuming cannabis.

Now, red eyes may be a common side effect of cannabis consumption, but not all cannabis consumers develop this side effect though.

In fact, there are several factors that come into play.

Why do some develop red eyes while others don’t?

As mentioned earlier, there are some people who are more prone to developing red eyes after consuming cannabis, compared to others.

The reasons for some developing red-eye while others don’t are:

THC content

The higher the THC content, the more intense and redder the eyes become.

Cannabis consumption

The more you consume cannabis, the redder your eyes can get.

Frequency of cannabis use

The higher the frequency of cannabis consumption, the more tolerance you develop to THC. The more THC tolerance you have, the milder its effects can have on you.

Blood pressure

People with low to normal blood pressure tend to develop redder eyes after consuming cannabis. However, those with high blood pressure don’t tend to develop the same intense red, bloodshot eyes after cannabis consumption.


There are some people who are allergic to cannabis. So using cannabis usually triggers an allergic reaction, a side effect of which is red, itchy eyes.

How to Get Rid of Red Eyes After Consuming Cannabis

Is eye redness due to cannabis consumption harmful?

Eye redness is a common side effect after consuming cannabis.

The intensity of its color may seem alarming at first, but this side effect isn’t dangerous or harmful to the eyes.

It’s just your body’s response to THC, and it does go away after a few hours.

The eye redness may look unsightly, but there are several ways though that you can minimize this effect or get rid of it quickly.

Choose cannabis strains that contain low THC levels

There are plenty of cannabis strains that have low THC and high CBD content. Some of these include Sour Tsunami, Harlequin, and Cannatonic. These strains can give you a good mental and physical high without producing strong psychoactive effects. Its low THC content also helps you avoid red, bloodshot eyes.

Use an eye drop containing tetryzoline or tetrahydrozoline to reduce eye redness

This compound constricts the blood vessels and decreases the amount of blood that flows through them. Using eye drops helps counteract the vasodilating effect of THC.

Drink plenty of water

In addition to eye redness, cannabis also produces cottonmouth or dryness of the mouth. Keeping yourself hydrated by drinking lots of water can help relieve some of these side effects.


If you don’t have any important appointments to attend to, then just rest and let it run its course. Rest and sleep are sometimes the best remedies to get over the side effects of cannabis.

Can the vasodilating effect of THC benefit people with eye problems?

The effects of cannabis on the eye’s blood supply actually have some clinical importance.

Several studies have shown that THC has the ability to relieve glaucoma.

Glaucoma is an eye problem caused by increased intraocular or eye pressure. Common causes of Glaucoma include optic nerve damage, eye injury, inadequate blood supply into the eyes, and eye infection.

The aqueous humor flows throughout the eye. It provides constant pressure that keeps the eye inflated like a balloon. To make sure that there will be no buildup of aqueous humor, the anterior and posterior chambers of the eye regularly drain some of the fluid. Their main task is to help maintain the eye’s normal intraocular pressure.

In glaucoma though, the aqueous humor’s drainage system isn’t working properly. Because it isn’t draining at its normal rate, the fluid then builds up and accumulates inside the eye, increasing the intraocular pressure.

Left untreated, the high intraocular pressure will constrict and further damage the eye. It will also impede blood flow and prevent eye structures from getting nutrients and oxygenated blood. All these can result in vision problems and, ultimately, blindness.

Now, THC’s ability to dilate the blood vessels also decreases the eye’s intraocular pressure. In fact, a 1971 study showed that cannabis consumption has the potential to reduce intraocular pressure by about 25% to 30%. This effect, according to the study, is dose-dependent and provides relief for about three to four hours after consuming cannabis.

But using cannabis for glaucoma has its disadvantages, too. You would need to consume cannabis every three to four hours to maintain that reduction. This, in turn, increases cannabis dependence or addiction risk.

Developing eye redness after using cannabis is normal, although there are some people who are less affected by it. This side effect isn’t dangerous nor is it harmful to your eyes.

In fact, the increased blood flow may even be good for you since your eyes are receiving more oxygen and nutrients. This effect can even be helpful to patients with glaucoma.

Of note, if you’re suffering from glaucoma, it’s still best to talk with your physician about the proper treatment for this eye disorder. Cannabis should not be used as a substitute for medications.


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