The study of the properties of drugs, medicines, and poisons is an old pastime that was originally practiced by the purveyors of medicaments and by professional poisoners. Until the end of the last century drugs were naturally occurring substances, organic or inorganic, most often obtained from plants so that the craft of materia medica (the collection and preparation of such drugs) was closely allied to the science of botany. Large formularies and specifications of such medicines were prepared (pharmacopoeias). The rapid expansion of the chemical industry during the last century has, however, resulted in the introduction of drugs whose numbers far exceed those entered in ancient pharmacopoeias.

Interest in pharmacology has expanded quite amazingly in the twentieth century, and its current growth rate has divided the subject matter into several separate but mutually dependent disciplines. These subdivisions include:

Several other specialized areas of pharmacology have now appeared and have received benediction in the form of journals to publish their conclusions. Such disciplines include: