I don't know that answer myself, lrks. Both are mind altering and vision altering when you get down to it... I remember trying to drive home drunk one night and and everything seemed a little blurry and things were going by so slow. Then one night I tried driving home high from pot. It had the exact same effect, just a little bit more intense because it made me so sleepy. Both are addicting, both cause visual impairment, both costs money, and both make you feel 'numb'... So I don't know why it's illegal. Will have to check into that.