Drugs seems a pretty good route.
It's not... I recently had a discussion with an ex pongo who had admitted to using drugs when he didn't in order to get out of the Army when he was 19. Now he's older and far more worldly he'd like to get back in... He may or may not be able to depending on circumstances.
Doing drugs or pretending you did is burning all your boats for the future.
As an ex gunner myself albeit a long time ago my opinion is that a quick get-out after 18 months is a no go... Suck it up, make the best of it and learn from it. It will stand you in great stead for the future. I'm lead to believe a previously enlisted Rock is currently in charge of security for the Olympics - you'd be surprised what Rocks go on to do.