You're entitled to privacy, too
keeping personal things private isn't lying. And it sounds like you're making sure that while you're not exactly sharing the reason you don't drink, you're also not crossing the line and downright lying to them, either. This is really admirable.
The choice to share anything personal (not just stuff like OCD) should be based on what your goal is in sharing, as well as the listener's ability to accept what you have to say. A lot of people feel they have to share things with their friends, but do not take into consideration how that info might affect them, because they are sharing for themselves, not necessarily for the benefit of their friends. So, you might want to be clear that you can trust your friends to receive this info and be okay with both it, and you. And, make sure this info will help them in some way (as in accept why you do not share their elbow bending at the local pub). If they're already ok with this, then you might want to ask yourself why it is you actually want to tell them, and what you hope to gain.
You're entitled to privacy, and that circle of privacy might be best to widen only when it helps both you and them.