Everyone responds differently. Depending on how long and how much damage was done can make a difference. What form of B12 are you taking? Cyno or Methyl? You can easily go up to 5000mcg/day. Methyl form would be my choice. You should probably also consider a B Complex. Chances are other nutrients are off too.

Regarding drinking. How much are you talking about? One or two beers, you should be fine. Please know that heavy use of alcohol will deplete the B vitamins. To play it safe, stick with soda water while out with your friends.

Do you know the reason for your B12 deficiency?