A drug refers to a chemical which interacts with the proteins in the person’s body for affecting a physiological function. This is, however, the general idea behind all the medicines. Hence, a drug and medicine mean the same thing. Once a person ingests a drug, it gets absorbed into the systemic circulation. It then binds with specific proteins which change the functioning of the cells to an extent. Consider, for example, the anticancer drugs tend to bind to the surface of the cancerous cells, which stimulates these harmful cells to die. So, in this case, the physiological action of this drug is cell death.