What are strategies for drinking less in a social situation or for avoiding driving while impaired?

Recently, many of my friends have been doing methamphetamines. Often when they start to come down, want to come down, want to "level" out their high, etc. they take Xanax!!! Now I know Xanax is an anti-anxiety drug, and meth speeds your heart up. So can mixing the two ("reds" with "blues") be especially bad? I keep trying to tell them that it doesn't sound like a good idea...but they know that I hate pills so they DON'T listen. "They know better!" But I haven't been able to find any info specific to my question in other places. CAN YOU HELP?

I have a history of "experimentation" (infrequent or occasional use of ecstasy, 'shrooms, and other drugs — mostly prescription pills). I am completely sober now, but am worried about long-term damage to my brain. I used drugs infrequently (no more than three to five times for each substance), but drank regularly. How worried should I be? Is there anything I can do to combat long-term effects?

I just started taking Zoloft today. I am going on vacation next week and am wondering if it is safe to drink while on this medication. I can't seem to get a straight answer from anyone. I'm not talking about drinking to oblivion; I'm talking about having a couple of drinks by the campfire. Is this okay?