People who become addicts don't like the highs and lows of the emotional roller coaster they're on, but it's the only way they know to cope with their emotional/physiological angst.
I've met someone who'd used cocaine 'recreationally'. His attitude was "been there, done that, don't need to use again."
Most of the street pharmacy's customers are self-medicating emotional pain. My mom didn't get hooked on the opiates her doctor recently gave her for her broken arm because she has a supportive environment.
The friend (who I've written about here before) relapsed on cocaine because she was depressed. Then she relapsed on heroin, supposedly to treat the high blood pressure cocaine gave her (but probably more because she needed something to 'numb' emotional pain). This was the summer before she met me.
Really I think she just must've been lonely. This week I found a copy of a book she gave me for my birthday after we met. She inscribed it, in part, "my heart melted the moment I first heard you speak."
I think I've successfully bullied her current court-ordered mental health providers into recognizing the mistaken diagnosis made by their colleagues in the other county. The earlier psychiatrists just thought she was "persistently disabled" because they didn't try to figure out why she'd become psychotic in the first place (doctor-administered depo provera birth control injections made her suicidal -> street pharmacy -> psychosis).