No sure about brain harm. But I used creatine for a few months and I got cramps in an intensity like I never experienced before.
I then decided it was not worth it for a few watts of cycling FTP increase. So I would not consider it harmless for everbody, but this sideeffect seems pretty rare.
I wasn't while cycling, it was when resting or at night sleeping. Could have been dehydration related, but i usually drink a LOT during and afterwards.
