I would have to say, its your life, so live it.
She is probably on an Ecstasy honeymoon, no matter how hard you try, she aint gonna give that up.
Sounds like she is old enough to know what shes doing, it would be different if she wasnt and you would be wise to intervene.
Trust me if shes on cookies or charlie she will be doing them weather you are with her or not, weather you try to stop her or just let her get on with it. Just hope she has enough grey matter to never let her self get on the smack. if she does its her fault not yours.
Most importantly you must realise that life is what you make it, and in most respects its too short, so get on with yours and let her get on with hers and learn her own lessons. The best advise you could give her if shes still crazy about you is, theres plenty more fish in the sea, my guess is if shes taking Class A drugs, and going out alot shes probably already had a few salmon fillets etc.