She might use drugs in her private time.. I don't know, don't WANT to know, and above all don't care.
But all the people saying she uses drugs on stage or during photoshoots?! That cannot be true. Drugs leave certain marks. Physical marks, like needle bruises or big eyes (you know what I mean), or other signs like drowziness or other weirdness. Ayu always seems very focussed, concentrated and she knows exactly what she's doing on stage. Not the signs of a drug-addict at all.
I trust her and don't believe this story