With drinking, it wasn't so much a bad experience (and there were plenty of those) as fatigue. I just got fed up with horrible hangovers, talking about stuff instead of doing stuff, repeating myself over and over again and having conversations that don't mean anything and that no one remembers. Plus, blackouts seriously worried me. I felt like I was becoming a bore, a danger to myself and just really, really tired.
With drugs, I had a few rough experiences, last was an MDMA OD a few years ago. I'm very reluctant to 'let go' so I ended up feeling like I was barely holding on to my consciousness, which was scary. I recovered from that but then again overdid hash butter on toast. If I hit cannabis too hard, I start telling people horrible things about them, which terrifies me and I have to self-isolate. These were all my mistakes of bad dosing, but they still left me feeling very 'meh' about drugs.
Leonard Cohen (Bird on a Wire): I have tried in my own way to be free
Mrs Hudson (BBC Sherlock): Sherlock! The mess you've made!