You say that you`re mates are all happy to do it, how do you know, have you tried to talking to them ? ( I know how hard that is )
Maybe for some of them, it`s situational peer pressure, same as it is for you ?
I don`t know how old you are mate, but sometimes you have to make some very hard life decisions for your own well being.
If your mates won`t accept you, unless you`re taking coke, then they`re not really your mates, as all you doing is enabling each other.
I had all this crap off some of my " mates " when I cut down massively on the ale, years ago, due to the meds I was on at the time and the fact that the hangovers were turbo charging my anxiety.
The lads I`m still mates with now, fully accept and understand that I can`t drink like them, because of what it does to me the following day.