Yeah, I heard the kidney problem before.

But it can also give permanent water retention if used heavily over-time.

I loaded on it once, and I found

- weak bladder...needed a piss twice as often
- water retention

So now I take it only before my weight training workouts, and it's great, no problems. It's like NOS for your muscles, you really notice it working when you get to the end of your workout and you don't feel so tired.