Do Diet Pills and/or Fat Burning Pills work?

Do they work? My local drug store has diet pills, and fat burning pills. Do they really work? and if they do, which is the best to get? Fat Burning Pills? or Diet Pills? and which brand is the best?
Update: I mean do they like help or give me a boost. Like if I'm on a diet and excersise, do they help out like give me a boost to lose a little bit more weight?
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