Coming from a very strict non-drug family I can honestly say that is the absolute worst thing to do. All it did was distance myself from them and forced me to lie.
then you have a full blown alcoholic and heroin addict.
I will tell my children from a young age (13-14) that I was an alcoholic and heroin addict, and as these things are genetic, to have a very discerning attitude towards them. I would want to let them know that they are free to live their lives as they please, weed isn't bad if you don't totally abuse it, and if they feel they are getting in a little over their heads they can tell me without me flipping my shit. If I find out they are using harder drugs, I will let them know the risks, tell them the facts of addiction, show them proper drug use for harm reduction safe, and show them there is a way out.
Also, if they are smoking or drinking, I'd prefer for them to do it in my home. That way I can accurately judge if they are getting out of hand
edit: damn, highooked got my points in before I could. stuff I believe in either way