Female Speaker: Are diet pills safe? Tracee Yablon Brenner: That's a tricky question because there are some diet pills that are on the market and are approved by the FDA but, I don t really think that's the best way to lose weight. They have some terrible side effects like diarrhea, they can cause your heart rate to increase, you really better off not going that route and if you do, you need to consult the doctor about that.