In order for a chemical to be considered a drug it must have the capacity to affect how the body works--to be biologically active. No substance that has the power to do this is completely safe, and drugs are approved only after they demonstrate that they are relatively safe when used as directed, and when the benefits outweigh their risks. Thus, some very dangerous drugs are approved because they are necessary to treat serious illness. Digitalis, which causes the heart muscle to contract, is a dangerous drug, but doctors are permitted to use i ....