ok, seriously, from everything i've read / heard drugs, smoking and alcohol all decrease somewhat the chances of getting pregnant because they can interfere with your girl's reproductive cycle. the flip side is people have sex when they're fucked up, and that's also when they forget about being safe. if she's on the pill, just have her ask her doctor. if he's not cool enough to answer her straight up and make her feel comfortable, she should get a new one...