Afaik does street ket often contain non-reacted precursors. They shouldn't be overly harmful but might contribute to the strain on the bladder, a phenomenon which got wide attention as of recently and it's not sure why it happens more these days, because of people doing more ket in shorter amounts of time or because of cuts/synthesis leftovers. Yeah, and fentanyl unfortunately the threat is real, even in meth it's found some times.
I'd suggest ordering from a deep web marketplace with reviews if you don't have a reliable dealer or to use the ketamine/methoxetamine derivates sold as research chemicals, it somewhat sucks that substances with less research behind them are more likely to be pure these days but it's how it is. Of course, my only official suggestion is not to use drugs, but you know what I mean xD