Buying any type of pills over the net can be dangerous, as some are made up in countries which don't control the contents - or, you simply don't get what you think you're buying.
The amphetamine-based ones which were popular in the 70's and 80's, were discontinued here because of people abusing them. They also caused heart problems and other body malfunctions. As the others've said, a controlled diet with exercise, is the best, providing a medical condition hasn't been diagnosed.