I feel the same way too - in my teens and twenties i did a lot of drugs, alcohol, ecstasy, speed, acid, mushrooms, coke, weed...
I'd be lying if i said it wasn't fun. Like the guy in Trainspotting says - the thing about drugs is that they are enjoyable - that's why people do them.
I do feel i learned a lot, there was a sense of experimenting with consciousness and experience. And just good old partying too of course.
But along the way, the fun and good times got less, and the chaos and carnage got more.
That's where i did a bit of a geographical and moved away from all my drug friends, and reconnected with my old friends from school.
I realised it had got to a point where i couldn't really enjoy things without a drug, and also was wanting a drug to cope with bad things in life. Basically i was an addict.
I found giving up all the drugs pretty easy - except one- alcohol.
This is because i just transferred all my drug addiction onto that one. The socially acceptable legal one with easy to find dealers.