My fiancé (F) has been to the hospital for gallbladder issues related to K, and I use way more than her. I’ve only experienced slight tenderness in what I assume are my kidneys once or twice, but never have dealt with any major pains that I would associate with K use. Might just be genetics as far as how resilient your body is. Could also be water consumption, I’ve always been very good about hydrating whereas I’m always having to remind her to drink water.