I used kratom to get off Suboxone after my doctor retired and I couldn't find an alternate quickly. Since then, I've been using some kratom most days before I can sleep as I have pretty bad muscle spasms in my legs. I don't know exactly how much I'm taking as I don't have a gram scale. I use a rounded teaspoon in a plastic spoon that's a little smaller than a regular teaspoon, down from a heaping teaspoon three times a day.
I have cirrhosis from Hepatitis C. I did the Harvoni treatment two years ago. They didn't know how much improvement I'd get with the cirrhosis from treating me and primarily did it to lengthen my life. Due to end-stage COPD/emphysema, I'd been de-listed from the transplant list as it's thought that I can't survive any surgery. My liver has recovered somewhat, and my last several blood tests have been mostly normal.
That includes while I've been taking kratom, so if kratom was liver toxic, I would probably know by now. It hasn't affected my bloodwork or any of the other tests that I still have at least twice a year--ultrasound, sometimes CAT scan, upper endoscopy. In fact, those test results have improved even after I began using kratom daily. So I feel pretty safe with it. Obviously, it doesn't affect everybody. That's not saying that it's not going to harm some people. BTW, I haven't had problems with my kidneys either before kratom or now, so at least for me, it's pretty safe. The problems with my lungs are mainly from 50 years if hard-core continuous smoking and possibly some years of injecting Ritalin pills. I'd be interested to know if the Ritalin shooting has anything to do with my lung disease, but it probably will only be detected if I'm autopsied. And then I won't care, because I'll be dead!%)