Ok, I know it's bad to mix meds with alcohol (I mean it says right on the label). But HOW bad -- I mean is it more damaging internally; or just worse for your disorder stability?

I'm guessing that most people on meds will have a drink or two, occasionally (at the least). I'm not a big drinker anyhow, but I don't abstain altogether either. My current meds are Lamictal and Adderall. I notice that if I take Lamictal IMMEDIATELY before I drink, that I feel much more intoxicated and extremely sleepy ( this only happened once).

Also, anybody know about damage caused by mixing benzodiazepines w/ alcohol? Obviously, would be fatal in high doses (of either when combined). I'm not planning on doing it, but I was just wanting some facts on the long term, or medical repercussions (yes, did it in past, but figured it MUST be bad, so stopped). My grandma actually has a bad habit of mixing these/sleeping pills with alcohol, so I'm also wondering about how it's affecting her health.
Thanks,
Jessie