To aid the fighting against weight gain, many drugs or herbal preparations have been used since 1940s. Some of them are withdrawn from the market because of the serious side effects. Fen-Phen preparations contained fenfluramine and phentermine while usnic acid preparations had sodium usniate, phenylpropanolamine, yohimbine, caffeine and 3,5-diiodithyroinine as ingredients. Fen-Phen usage caused cardiac valvulopathy while preparations with usnic acid caused serious liver toxicity. Furthermore, there were several reports of deaths in patients taking these two kinds of preparations. Although fenfluramine is no longer available, physicians can still prescribe phentermine and preparations of usnic acid are still available on internet sales. This review will focus on Fen-Phen and usnic acid preparations and the possible toxicological outcomes in the usage of these two kinds of preparations.