Depending on what you drink, they may go up intially - ie alcopops, fizzy rose wine etc and beer is quite carby too. I drink spirits and diet mixer, and red wine is ok diabetically wise in terms of bg.
However, it does, as quite rightly pointed out, lower it some hours later. So my advice would be (depending on how much you drink) test test test. I try to start testing regularly about 4 hours after I start drinking and do it regularly from then on in. Also, before bed ALWAYS ALWAYS ALWAYS.
I tend to snack whilst drinking but this can have you a bit higher than youd like but for example, I went to bed on a 9.3, didnt snack, thought Id be ok and woke up at 2.3
Of course, hypos and hangovers are very similar so never a good mix!