[egfr]

Careful.

Creatine metabolizes into creatinine which is major indicator of kidney function because not being able to clear creatinine means your kidneys aren’t working. Adding more creatinine to your system decreases your ability to clear it leading to fatigue, edema, high blood pressure etc.

So it isn’t bad for your kidneys: it is bad for everything else.

[nerevarthelame]

Creatinine can be an indicator that your kidneys are not working well. It's a cheap red flag that can be screened for in a common blood test. But if heightened creatinine is a result of one's creatine supplementation, then there are none of the downsides associated with kidney disease.

Creatinine itself doesn't cause fatigue, edema, or high blood pressure. Kidney disease does.

[tensor]

Except many many many decades of research has not shown any of that to be true.