The kidneys are normally able to filter out a large amount of craetinine on a daily basis.
There is, still, no scientific proof about kidney damage due to creatinine used in large amounts as a supllement.
However, the kidneys in that case will need to work harder to excrete the excessive amounts of creatinine.
Forming frequent kidney stones is complication of using supplemental creatinine.
Suppression of the body's ability to synthesize its own creatine is one of the most serious complication of using creatinine as a supplement.