Wasn't that big a deal to me. I had a bad headache for a day, and the shits for a few days. The more healthy you are the less you'll feel the detox I guess. Some people get REALLY sick though taking too much at first. It's nothing harmful, just uncomfortable. Which is why it's a good idea to start with 500mg and increase by 500mg weekly until you are at the dose you want. You'll still remove toxins just at a slower rate.