I will probably get in a lot of trouble for saying this: don't voluntarily admit anything. If it isn't on your record, it never happened. I really appreciate that ya'll want to do the right thing, but don't incriminate yourselves. If you've smoked weed in HS, don't admit it. If you drank underage, don't admit it. Move forward with a clean slate and stop doing those things now. Being honorable isn't worth having your application denied, because there are no sympathy points for honor. Like I said, I know this is the WRONG thing to say, I know as a cadet I should be honorable and all that, but I hate to say it but that is not how West Point works. If it isn't on your record, it never happened. Self admitting to things that you didn't get convicted of will only hurt you when there is no need.
On top of that, there are a number of ****bag cadets who abuse drugs and drink underage. There's practically an alcohol board for underage drinking every month. There's more of an issue with drugs then you'd probably imagine, cadets get kicked out coming back from leave and popping hot on a piss test frequently. I tell you this not to disparage USMA, but to frame your concern. There is a large group, dare I say majority, who might have abused drugs or drank in HS. It's too common these days to avoid. As long as you realize who you'll represent as a cadet and stop those activities now, I would say don't self admit. Most of the cadets here did that. The reality is no one is perfect, despite how bad USMA would like us to be, and that everyone has messed up before. If we all self reported each time we broke the law on our application many of us might not be here. If nobody self reports, then reporting will only hurt you.
Food for thought, feel free to disagree. I just want to lay out my opinion for consideration.