I have a fairly good tolerance. I've never been buzzed off a single bar-sized mixed drink (unlike alot of girls I know), but then I don't chug and I make sure to eat beforehand. And I'm 5'9" and average build, so it's got places to go. It's all a matter of being smart: if you're going to drive, have one drink with food and give it about an hour to get out of your system, and then you know for sure you're safe.
If you're just curious about your tolerance and what certain levels of alcohol can do to you, start out slow. Pick one drink for the night, sip it slowly, chug water in between, and see how far you get before you start to feel gross. Don't do five different shots in 10 minutes and then wonder why you're puking everywhere. I try to find that point where I'm nicely buzzed and maintain it over the course of the night--I like being silly, but not stumbly. Be wary of sugary drinks that mask the alcohol; it's easy to chug a bunch of those without thinking, and all the sudden you're trashed.
As far as alcohol and meds go:
here's the FDA warning regarding ibuprofen, and it looks like you don't have to worry about that unless you're planning on becoming a heavy drinker. Liver damage and stomach bleeding happen when your system is consistently overloaded. What you should check before you drink is the alcohol interaction with any prescription drug you're taking. Anti-anxiety meds and sleep aids are usually bad to mix with alcohol--since they're both depressants, the mixture can slow down your system too much and send you into a coma or kill you. You can find that sort of info on the large folded pieces of paper they stick in the prescription bags, or by doing a search online.
I've read about studies that have actually found that the longer a woman has been a heavy drinker, the less her tolerance is.
It is my belief that a good amount of being drunk is in your head. I start to act and feel goofy like I'm drunk when I'm around alot of drunk people, even if I've had literally nothing to drink. When I am drinking, I make more of a conscious effort to be in control, so I often end up behaving less drunk when I am drinking than when I'm not (unless of course I'm completely trashed and not just buzzed). I actually read about another study (how nerdy am I) where they gave half the group regular beer and half the group non-alcoholic beer, and everyone acted (and thought they were) completely drunk. (I have doubts as to this study though, since the non-alcoholic beer I've tried is clearly non-alkie and tastes like shit to boot).
The other thing about alcohol: people start behaving more like themselves when they're drunk. Someone who's obnoxious sober is going to be
really obnoxious drunk. Take away the inhibitions and you start finding out who people really are, which can be fun but also can be a problem if you're not in the right setting. Getting naked and dancing around drunkenly is great when you're at home, not so great when you're at an office party, you know?
Jam it back in, in the dark.