No amount of peer pressure is worth what little so called respect you may gain from the people around you. Most of us will have been in a similar situation when friends may be smoking dope etc.
It's their choice, worry about them second look after yourself first.
Having studied pharmacology (well partially!) at uni I got shown the lists and lists of adverse effects from so called 'safe drugs' such as paracetamol.
There's a reason why drugs are illegal, its not to stop people having fun, its because it can destroy you. Some drugs are cut with glass, sand and all sorts, one of the biggest risks with drugs is that you never know what you're getting.
Rant over, sorry if I sound like a stupid mare with little sympathy...I'm not!Stick to your guns over this one, in my opinion nothing is worth the risk of not.