Drug users use a lot of drugs
You can find a bunch of papers like Ketamine: An Important Drug With A Serious Adverse Effect, where they say that ketamine is potentially great for depression, but that the risk of bladder injury needs to be taken really seriously. A standard psychiatric dose of ketamine might be 0.5 mg/kg IV, 2x/week, for four weeks. Drug users use a lot of drugs! So why don't psychiatric patients get bladder injuries? It's because you get bladder injuries when you're taking more like 90,000 mg of ketamine a month, and not when you're taking 280 mg. There is one case report in the literature of somebody getting a bladder injury after taking prescription ketamine in a clinical setting. See eg Controversies of the effect of ketamine on cognition, which is speaking for the psychiatric consensus when it says that "Although ketamine might seem like a promising antidepressant that could relieve treatment refractory depressive symptoms, the induction of memory impairments in the longer term is of concern". The most important reason meth makes your teeth fall out and ruins your life but Adderall just makes you study a little harder is that the meth users are taking 50x higher doses. Don't go out and take a mix of ketamine and amphetamine, then tell the cops that it was "Just a clinical dose" and "This blog on the Internet told me it was okay".