^^ I think they definitely do. Both through directly impacting your health, but also indirectly - through worse nutrition, higher stress, and a higher risk of accidents/violence just by being in the drug world...
They definately impact your health but I'm not too sure about the worse nutrition and higher stress part of it.
I'm probably what you'd call a heavy user of MDMA, almost every weekend for the past few years or so, with months off here and there, using base and coke occasionally and drinking a lot on weekends.
However, I'm as fit as I've ever been due to sport and gym all week and the only stress I'm facing is from uni exams this week, so I did have this weekend off the gear.
But my nutrition is excellent and I'm very healthy.
What I'm saying is that just because I use drugs doesn't mean it is negatively impacting the rest of my life. During the week I'm a different person, but on weekends I just love to party. I have never increased my drug use to during the week, I don't even drink during the week, too much stuff to do, but on weekends I definately let loose.
It is a lot about self control and knowing what you want. I'm using drugs the same now as I was 3 or 4 yrs ago when I started. Probably the main thing I've noticed is that my short term memory has been affected a bit, but I'm currently taking piracetam and choline bitrate to help combat that.
This is just my personal opinion on it, of course not everyone is the same!