The only diet pill that I know of that is "safe" is alli. It works by blocking some of the fat you eat and adding to your weight loss. It won't make you lose weight on your own but it will help you lose more weight then you would without it. It's important that you follow the alli plan accordingly because it can give you treatment effects. Also if you decide to take it, make sure you take a multivitamin. (removed outbound link)
Good luck and follow the instructions exactly if you decide to take it.