Does excessive use of illicit drugs eventually mean that the brain stops functioning properly?

I myself have taken many drugs in my time and I can now say that part of my life is over. While I don’t regret going through those experiences I can’t help thinking that the long term effects of such behaviour have been detrimental to my well-being and Mental state.
I am on medication because of it and just wondered if anyone agrees that you don’t need to use drugs in order to achieve transcendental states of mind.
Do the negatives of drug use outweigh the positives?