"Splenda (sucralose) is the best selling artificial sweetener. It is made by substituting three chlorine molecules for three hydrogen-oxygen groups on the sugar molecule. This changes sugar into an artificial sweetener that can't be metabolized, meaning our bodies can't digest it or derive energy from it.
The safety of Splenda has been controversial for some time. Citizens for Health, a nonprofit group, maintains that adverse effects ranging from stomach pains to headaches and skin rashes have been reported by users. In April 2007, the group petitioned the FDA to withdraw approval until more is known about the sweetener's safety. To the best of my knowledge, studies on Splenda – those attesting to its safety and those warning of dangers – have all been done in animals. I can find no human data demonstrating that Splenda can cause any health problems; nor can I find human data proving its safety. I would follow the precautionary principle here and avoid it.
If you use artificial sweeteners, there's no proof that I've been able to locate that these products will actually help you lose weight. In fact, circumstantial evidence suggests that they may make matters worse: the number of Americans consuming artificially sweetened food and drink rose from 70 million in 1987 to 160 million in 2000. During that same period, obesity rates rose dramatically." -http://www.drweil.com/drw/u/QAA400414/Sweet-and-Natural.html