i know how to handle parents. Ur dad reacted the same way mine did (but mine didnt stay like that for long ) the best way to deal with this and be 100% honest. However, you CANNOT just jog along with what ur parents are saying. This is VITAL, you do all the talking, listen to what your parents say and then make a valid point.

Tell ur parents about the DXM, it isnt illegal witch will help, BUT MAKE SURE U TELL THEM THAT UR GIVING UP (AND DO) BECAUSE YOU HAVE DECIDED ITS BAD FOR YOU.

NEVER ARGUE WITH WHAT THEY SAY, tell them you dont agree, but stay emotionless, and for gods sake, dont get angry

Be assertive, but dont push it.

Make decisions in front of them, you have got to lead the conversation you have to do 80-90% of the talking.

Dont promise to do somthing when you know full well you wont do it.

the two golden rules:

BE 100% honest, nobody can fuck u for honestly and u sound MUCH more convincing.

DO NOT CHANGE YOUR OPINION, make a game plan and stick to it.

Your parents are people too. Act like an adult and an equal, and that means taking responsibility for your actions, if you make a mistake, say sorry. If you disagree with somthing they say, be poilite and say you disagree (then back it up with a strong arguement)

Hope u followed all that but trust me, i'v been busted by LOTS of people, and u haven't met my dad...