I don't think it would really be a big obstacle for anyone if they were determined to get some. In the worst case scenario it may make you turn to the streets and the majority of what's on the street opiatewise is heroin. I don't think it's the best idea.
When you're really feeling positive about not taking anything, try to write down what exactly is motivating you to do so. Try, say, wording it as a letter to yourself and word it strongly. Maybe that way when you're feeling bad and are tempted to take something you can read it and it'll change your mind.