The active ingredients that promote weight loss (the ingredients included in virtually all weight loss drugs) are more damaging to the body than they are beneficial, that is certain. These are drugs in a group of drugs classified as anoretics. Anoretics, or "anorexigenics" come from the same root word as the disease known as anorexia. These, the active drugs / ingredients included in any number of specific brand-name, over the counter drugs, do many things. Most importantly for the market, they suppress the desire to eat. The curbing of someone's hunger is not a bad thing - especially if someone wants to loose weight to get healthy. But suppressing your appetite will only make you feel the need to eat less.
You still require certain nourishment to sustain yourself, but with hunger suppressants--time will sail by and there is a great tendency to ignore if not completely forget the need to eat. Malnourishment is bad for anyone, and can lead to a large number of mental as well as physical complications. Therefore, simply not eating is risky enough with the possible development of malnourishment - with or without weight loss pills. But realize that this is only one horribly damaging possibility in addition to all of the other potential dangers that come with the regular use of weight loss pills. Risks such as pulmonary disease, strokes, and heart failure are all too common side effects for someone trying to treat a weight problem (real or imagined) with fast-acting diet pills.