Any possible side effects when doing a colon cleanse?

Can any side effects be expected during the cleansing process? I am using Sculpt N Cleanse by Health Direct and started breaking out with hives since starting the program (been on it for 3 days now). Not sure though, if the hives are caused by the product or if its just coincidence. I have a history of breaking out with hives, but the last time was about 6-7 years ago, and at that time it seemed like it was because I was getting overweight, which happens to be the case right now. Any info would be helpful.