My girlfriend is throwing her life away and I want to tell her that.
Why do you feel that way?
Because she is delaying a lot of things in her life
I feel worried about some of my family members and friends as well, so I understand your need to tell your girlfriend that she is throwing her life away. But I would tell her very calmly and politely, so that instead of her being angry at you she would feel that she has someone that cares for her.
It's ok I just want to tell her that she should stay away from drugs.
You're right that you should let her know this, you sound like you are being very supportive. That's nice!