Simha - I think the usual guidance is to be mindful when drinking, because alcohol can make bloods erratic. They usually drop, then depending on the type of alcohol - wine, beer, spirits, will likely rise a little (maybe back to where the person started, or higher if it was a sweeter wine or beer.
Personally, I don't drink much and can have periods of weeks or months when I just don't bother with alcohol. When I have a glass of wine or a G&T after that, I find my tolerance has fallen away a bit. Some folks also find if they lose weight their alcohol tolerance changes.
I appreciate that the Metformin information leaflet talks about no alcohol, but I have read of many members questioning this with their doctors, who have been content, provided it's in moderation.