I'll probably get flamed, but if you're likely to abuse the drug and you're of an age to be living in your parents' home, then I'd say they have more than every right to control whatever aspect of your life they see fit. If it doesn't suit your style and you feel they have no right to do so, then the alternative is to set out and set up a life and home of your own.
There's a reason your parents are controlling your script, and I'd say one fairly compelling reason is the fact that you're posting on a drug website along with the rest of us who use legal and illegal substances for recreational purposes. It suggests you have a history, or at the very least more than a passing interest in drug use for more than medical purposes.
Please don't hate on me, but it's the truth.