Diet Pills are available in three different varieties – prescription, over the counter (OTC) and herbal supplements. The only way to buy prescription diet pills is with a medical doctor’s prescription. Prescription diet pills are tested and consistently monitored by the Center for Drug Evaluation and Research at the Food and Drug Administration (FDA). You can buy OTC diet pills at a drugstore, pharmacy, health food or vitamin store. OTC diet pills are still watched by the FDA Center for Drug Evaluation and Research. To buy herbal diet pills or dietary supplements at drugstores, supermarkets, vitamin and health food stores. The FDA considers herbal diet pills to be food products, which belong to the control of the Center for Food Safety and Applied Nutrition which is subject to different guidelines than the Center for Drug Evaluation and Research.