Creatine tends to draw water into the intestines, causing some to get an upset stomach after taking it. This can be minimized or even prevented in one of four ways:
By mixing creatine in hot water to increase its solubility
By eating creatine with meals
By spreading the dose throughout the day rather than taking it all at once
By switching from creatine monohydrate to either "micronized" creatine monohydrate, or other more water-soluble forms such as creatine HCL or creatine nitrate.