Why smoking marijuana makes your eyes red.

One effect pot does have is it raises the blood pressure temporarily. That is why people who smoke it get “red eye-“a condition where their eyes turn red because of the engorgement of the blood vessels.  

It is known as one of the effects of marijuana  abuse. First here is a site with 50 possible causes of Red eye.

http://www.wrongdiagnosis.com/sym/red_eye.htm

Dont listen to those guys, let me tell you the real reason...THE REAL reason why your eyes turn red is because when you laugh so hard, all of the blood rushes to your head, thus ENGORGING the eyes with blood.

ljsafg your wrong, the capone guy is right

your eyes get red because u  r turning into an allien to be adpoted by gods and fight the evil powers

when your smoking a blunt it never fails your eyes get red because it woulod be good weed if your eyes didn't turn red, DUH!

i heard it makes your eyes red cuz it dries you out. ever notice ur sinuses clear as well as getting a dry mouth. now that i think of it, maybe just ur face gets dried, anyways thats why drops work they hydrate.

Marijuana decreases pressure in the eyes and increases blood flow. When this happens, the arteries in the eye-ball expand (due to decreased pressure). These areteries, especially when expanded, are visible in the white portion of the eye and make the eye appear "bloodshot" or red.

This very result (decrease of pressure in the eye) is the primary reason marijuana is used to treat glaucoma. Glaucoma is the condition where there is excessive pressure in the eye. In some patients, the pressure can become so severe that it causes damage to the retinal nerve, ultimately damaging the patient's vision. Marijuana decreases this pressure.