Oh, and one last thing....
I totally get what CelticP is saying about his parents trusting him. My parents were exactly the same way. They had the talks with me about drugs and alcohol. It's what made me a responsible human being. Because of my sense of responsibility, I know my limits and even knew them as a teenager. It doesn't mean I never drank or did anything irresponsible... I just knew the limits to which I could go without putting myself or others around me in too much danger.
Drugs and alcohol aren't going to go away. They are something that your teenage child WILL be faced with, no matter what. If you drink occasionally, and had the occasional drink in high school, how on earth can you NOT feel like the biggest hypocrite on Earth if you tell your kids not to drink?? And believe me, kids aren't stupid, they will see through your hypocrisy right away. (same with drug use - my friend's mom was a druggie as a teen and told her NOT to do anything, even pot, or she'd get kicked out of the house... needless to say, my friend got kicked out of her house)
I have a son now. And I say this with all honesty and I will try my hardest to uphold it when the teenage years come around.... Kids need to be free to make their own mistakes. Yeah, it only takes one major mistake to end a life, but most of the time it doesn't come to that - there's usually a build-up and warning signs before that happens (at least with drugs/alchohol - car accidents, on the other hand, scare the crap out of me because they come out of nowhere!). The best we can do as parents is to educate them about the things they will be confronted with and let them make their own choices. We need to be there to pick up the pieces and talk it over with them if they fall... not to say 'I told you so' but to say 'I understand... now, how are you going to handle this from now on?' But they also need to LEARN from those mistakes. If they keep making the same mistakes and they're not learning, then it's time to get a little tougher.
Now, if you really did avoid ALL drinking and all drug use in your teenage years, preach away... but don't be surprised if your kid comes home drunk one night... it's how you deal with it at that point that helps or hinders the future outcome. If you go into a rage, guaranteed that your teenager will be getting drunk a lot more often than otherwise. At least in our family, light teasing and embarrassment went a LOT farther than rage! I was very keen to avoid the embarrassment, so I just didn't do it again
Rage, on the other hand, tempts a lot of teens, especially if their parents are the type that just don't pay attention to them unless they are mad about something.
Ah, parenting - it's so important but so hard to do well!!
BTW, I highly recommend this book to anyone with kids:
https://www.nationofwimps.com/