I used and abused codeine for years and years before legislators changed it to prescription only. When it changed, I ended up using heroin. I only used heroin for about two weeks before I sought opiate replacement therapy for the whole addiction (first suboxone, then subutex, then methadone). None of them made me feel like heroin did - all of them gave me a nausea that rendered me unable to leave the house because whenever I'd move, I'd vomit. Heroin made that constant suicidal ideation that nags in the background just fade away.
So now I just smoke weed, and take a tiny bit of codeine each day that I get prescribed. The heroin was short-lived, but it's fucked me. I think about heroin every day. It's the only time I have ever felt completely at ease in an existential sense.