What are some negative effects of creatine?

Generally, Few. Creatine can cause an increase in water weight. It has been associated with stomach pain, nausea, diarrhea, and muscle cramping. There is some concern that it could harm the kidney, liver, or heart function. Drink extra water. If you are taking creatine, don't exercise in the heat. It might cause you to become dehydrated. Do not use if you have kidney disease, diabetes, or may be pregnant.