Why Do My Eyes Turn Red When I Smoke Weed?


Among the most common side effects (and telltale signs) of smoking cannabis is red, bloodshot eyes.

As those who regularly consume cannabis can tell new users, there is nothing to be concerned about your red-eyed circumstance. You’re not experiencing an allergic reaction or some bigger complication. It’s a completely natural occurrence when smoking cannabis.

In fact, your eyes turning red has nothing to do with the act of smoking at all.   

Under Pressure: Lower blood pressure and dilated capillaries  

After consuming a cannabis-based product (flower, concentrate, edible, etc), users generally experience an increase in heart rate and blood pressure. This is due to the plant’s cannabinoids, which are chemical compounds responsible for some of the therapeutic and medicinal benefits of cannabis, and their initial interaction with the body. This rise in blood pressure and heart rate is comparable to normal physical activities like exercise or sex.

It generally takes about five to ten minutes for users’ heart rates to return back to normal and for blood pressure to begin to decrease. Lower blood pressure leads to the dilation of blood vessels and capillaries, including ocular capillaries. The dilation of ocular capillaries causes increased blood flow to the eyes, which results in your eyes turning red in the process.

It’s cannabis’ ability to relieve intraocular pressure in the eyes that makes it a viable treatment for glaucoma, a group of eye disorders that causes damage to the optic nerves which can eventually lead to blindness. It’s also why your eyes become bloodshot.

The Redder the Better?

The amount your blood pressure is lowered and how red your eyes become depends on the amount of THC you consume.

Tetrahydrocannabinol (THC), the most common and well-known cannabinoid in the plant, is responsible for the intoxication associated with smoking cannabis. The greater the concentration of THC in a cannabis product, the stronger the effects and the redder your eyes become.

So red eyes can act as a sign that your cannabis has a high cannabinoid content (it’s potent).  

Other than being a dead giveaway that you’ve recently consumed cannabis, you have no reason to be concerned about the redness of your eyes. Cannabis-induced eye redness will typically only last a few hours.

Still, it isn’t a bad idea to have eye drops on hand.