Marijuana has a half life in your body and breaks down slowly in your body. The more often you smoke marijuana, the longer it takes for your body to remove the substance. If you smoke once with an otherwise clean system, it can take 3-4 days to have the marijuana completely removed. If you smoke one day and then again on day 3 it will take over a week to be clean again, and the time builds the more often you smoke until you reach 45 days total.