When alcohol enters the bloodstream, it takes a day at MOST to rid of it. When Marijuana enters the bloodstream, however, it takes a MONTH for it to be completely disposed. The effects may go away, but it is still there. You may think, "so what?" If a police officer pulls you over a week after you were wasted and performs a blood test, the officer will find nothing wrong with you. If a police officer pulls you over a week after smoking Marijuana and performs a blood test, guess what, yo ass is gettin' sent to jail. *edit* That is, if you are in a state where the drug is illegal.