I read a good sentence somewhere recently about what to say when offered a drink and it was along these lines...
Thanks but I feel better when I don't drink alcohol. A sparkling water/lime and soda/whatever would be lovely though.
Say it with a big smile and it's non confrontational or judgemental, to the point and doesn't leave much room for arm-twisting.
There is always the driving/medication route aswell or the I did Dry January and felt so good that I've carried on line too.