Well, I was one of the few unfortunate ones who had a near-deadly reaction to it, called 5-FU toxicity. Thanks to a Mayo Genetic Oncologist quite a few years back, there's now an antidote, but I warn everyone using it to just pay close attention to any sudden severe symptoms. It actually destroyed my liver and I'm now on the transplant list. Mine is a rare case, though. My husband and two neighbors have used it and had very successful results. Mine is apparently a genetic issue.