Being a young teenager with drugs at parties you go to is an incredibly difficult situation to be in. Unfortunately as the modern world is progressing it is getting far too easy for teenagers to get their hands on illegal substances putting increasing numbers of children in these dangerous environments.
It's hard to miss that the issue you are facing in particular is the peer pressure surrounding the whole issue. Picture the scene. You're sitting with some mates at a party having a great time maybe with a couple of beers, then someone pulls out a little bag. Everyone around you seems to be getting excited and you feel like the only person who wants to back away. No teenager wants to be the killjoy and every teenager wants to be the life of the party. Now obviously, as every person you ever ask will tell you, just back away. Or even say no and act cool about it.
You don't have to make a fuss that you don't want to be involved. But I know from experience that as soon as you're involved it's very hard to get back out. I luckily managed it but had to starve myself of parties for a few months, and I'm sure you don't want to be doing that. Think about the consequences of being involved in drugs and you will instantly see that the 'benefits' certainly do not outweigh the downsides. If you are caught by the police for any link with drugs under the age of 18, you are almost definitely going to get sent to magistrates court and given a permanent drugs record.
This would mean that you can't travel to the US for the rest of your life. That shuts off so many opportunities on the long term. Almost every job opportunity could be affected by that. It's also very difficult to get into a university/college with drugs on your record obviously. If you are a sportsman you will 99% of the time get kicked straight off any team/club/academy you are in for obvious reasons.
A lot of boys in their early to mid teens will start smoking and drinking because they think they look really cool in front of girls. If you stand up for yourself and be mature, they will fall to their knees for you.
I know it's hard from experience. But do whatever you can to just not take the drugs. You can still be friends with the guys who are. Act cool when they are taking it. Try not to mention it too much and you will be absolutely fine. Most people will move on from the drugs issue, come to their senses and mature like you already have very soon and all these troubles will disappear.
The drugs are unnecessary, pointless and massively harm your health. Nobody in their mature and right mind would do drugs.
I'm very happy you've brought this issue up and I wish you the best of luck. If you every have your own gatherings state there will be no drugs at parties you host.
You are clearly very mature so I'm sure you will pull through this phase and your real good friends will follow you, I can guarantee.