Are there any side effects of oral creatine supplements?

Yes: The most common side effects are stomach pain and diarrhea. There is also weight gain, and many athletes who use it have muscle spasms. Used in recommended doses, it appears to be generally safe.

There are some: Side effects of creatine supplementation are: abdominal pain, heart rhythm problem, dehydration, diarrhea, high blood pressure, muscle cramps, nausea, renal dysfunction, rhabdomyolysis, weigh gain, seizures, .. (source: medscape).