You may get red eyes due to substance abuse but having this condition under normal circumstances may be a sign of something else. You get red eyes when the surrounding blood vessels expands or shrinks. This can be due to smoking weed or any other aerosol drugs. But an infection or a foreign particle in the eye may also cause it. Ifthis is due to any foreign object it is not a dangerous situation as the object can be washed out. But if it is an infection then you must consult your doctor immediately. If the redness disappears with time