I will however give you two pieces of advice. The first is to open up communication with your daughter. Ask her – If you are open and honest without being judgemental you may well find that she tells you the truth and this can only be a good thing for your relationship.
My second piece of advice is not to fear drugs. Whether we like it or not drugs are endemic in modern culture. There are many different types of recreational drugs and drug taking lacks the stigma that it used to have. Chemical recreation is certainly not something I would encourage but nor is it an indication that your daughter is on any kind of downward spiral to throwing her life away. Again, I wouldn’t say all kids do it but a good many do and I’ve known plenty who have gone through drug taking as a phase and moved onto more socially acceptable pastures new.
Image http://www.sxc.hu/browse.phtml?f=view&id=489545 (rotorhead)