first off u don't need to make an announcement re not drinking. in a drinking situation how bout just saying you're off the stuff right now? if they respect and care for u they won't take it further.
word of caution-i will admit tho that some drinkers-your friends, etc- might get antsy cause they may be secretly worrying bout their own drinking consumption and/or they won't want to lose their "drinking partner". don't buy in to their encouragement for u to drink.