The main reason your eyes get red — or bloodshot and bloated — when you use marijuana is due to vasodilation being set off by THC and other cannabinoids present in cannabis.

Can’t folks just buy marijuana recreationally? In this Eye on New Mexico episode, we sat down with NMDOH’s director of the Medical Cannabis Program to ask all those questions and more.

The eyes look red because cannabis causes blood vessels to expand and fill with more blood. THC can also lower pressure in the eyes, which can ease symptoms of glaucoma for a few hours.