Clearly, your wife has a problem. A massive one. She may think its all fun to do drugs for a night out but you can't just get on and off drugs whenever you want, the addiction will stay for life and only get worse over time, unless she seeks help! Yeah, maybe all her friends are doing it and its great fun for a couple of hours or a night out but think long term.... is this how she sees herself in another 5 years time? Would this be the biggest achievement of her life in her younger years when she could have done so much more?? I think you should really push her to think it over or consider leaving her otherwise.... it could be she feels she can do whatever she wants as long as she has someone to come back to at the end of the night.
And don't do drugs just for her sake, you are just showing her its ok to do it, which its not!! It wouldnt help matters if you got addicted yourself coz then you're both well screwed.