Are fake doctors giving you drugs in the form of medicine to cut on weight?

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I just saw the movie " Requiem For A Dream " and was horrified to see how a sound old lady turns insane, after she visits an unqualified doctor, who gives her some pills to cut weight, those pills have huge side effects and disturbs the lady's mental balance! Is this something happening in real life? Do we need to recheck on what pills are we given?