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?

There seems to be no advice or information on the subject of alcohol poisoning that I can find on your web site. Recently I had a very bad experience that I think must have involved alcohol poisoning, and would like to have some information on the causes and signs of alcohol poisoning. Does beer before liquor have anything to do with it?

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.