Hethcliff, I'd say 8 weeks, if you use 10+ g/day. If you use smaller doses, you could go longer. Drink a lot of water and you may not even have to worry. It seems to run in families. Creatine citrate is a form that is nice to the kidneys, but I get UTI's after about 6 weeks, so I always use it for shorter periods. Most guys don't have any prob if they stay well hydrated.