My best friend ignores me what should i do?

in my opinion, I would say this "friendship" is a lost cause. You say neither of you have much in common, and that she's always making up excuses to why she can't hang out...it seems that she's found her set of friends and you've found yours. I would recommend you to continue focusing on your studies, and not associate with this girl whose new habits are likely to bring you down...you seem like a smart cookie, and shouldn't get involved with someone who's trying drugs and can interfere with your education. Boy I wish I wouldve taken my own advice haha...but seriously, friends come and go. Even the ones who you've known for a lifetime. Its not worth getting upset over, but you should just treat it how it really is: an ordinary cycle in life. Unlike your wayward friends, the knowledge you've devoted yourself to will stick with you for your entire life, and never leave you or bring you down like a friend could. Just cut off all contact and keep your nose in the books! :)