What is, overall, safer for your body: alcohol or marijuana?

My dad requires me to take weekly drug tests since he found out that I was smoking marijuana. My first test came back positive for marijuana and cocaine. I was not surprised about the marijuana because I had only been clean for five weeks, but I have never done cocaine. Is there anything that could have triggered a positive result? Could opium or mushrooms or any other drug possibly trigger this positive result?

1) I found a white powder in my friend's car and I think it might be cocaine. I'm not sure if it is or not. I don't know if I should confront him with it or what I should do. I don't want to see my friend get hurt, but if I'm wrong, I don't want to falsely accuse him of something like this. How should I go about handling the situation?

2) I am a first-year business student and have a little sister who is a junior. I think she is doing cocaine because I found some "paraphernalia" in her room last week. What can I do without damaging my relationship with her?

Do different kinds of alcohol (specifically liquor) actually make you different kinds of drunk? Or is it a cultural/psychological thing? I've noticed that I feel different when drinking wine vs. vodka vs. tequila, and I'm wondering if there's a physiological reason.

My 21st birthday is coming up. I've already had two sets of friends and my mom's boyfriend offer to take me to the bar for drinks. The problem is, I have never been drunk before, let alone consumed alcohol. I chose not to drink for a few different reasons and am not sure if I should change anything for my birthday. On the other hand, I feel that I am obliged to go out drinking on this "special occasion."

I am a healthy, fit, 18-year-old male. I have tried both ways: consuming small amounts of alcohol regularly (one standard drink a day) and consuming a lot of alcohol irregularly (10 to 20 standard drinks in one night, but only two days a month, or thereabouts).

I have tended towards drinking a lot irregularly because I have found that I can't notice any effects until I have had at least four or five drinks, 80 to 100 proof shots, usually mixed with soft drink.

I was wondering if either way was less healthy or more of a risk as the same amount of alcohol is ultimately consumed. Also, I noticed that I got a bit more of a 'beer gut' when I had one-a-day than 15 at once; is that likely or just my imagination?

I have ADHD and am prescribed 30 mg of Ritalin a day. However I also smoke pot at least once a week. Is it okay to be smoking while on Ritalin?

Recently (the last six months or so) I've been getting really tired after a couple of drinks (let's say three or four). By eleven at night, I'm ready to call it quits. My friends and boyfriend poke fun at me because I usually head home before they do. How can I last longer in a healthy way? I definitely try to drink water throughout the night, but is there anything else?