What is Pharmacology?

WHAT IS A DRUG?

For the purposes of this book, a drug can be defined as a chemical substance of known structure, other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect.

A few points are worth noting. Drugs may be synthetic chemicals, chemicals obtained from plants or animals, or products of genetic engineering. A medicine is a chemical preparation, which usually but not necessarily contains one or more drugs, administered with the intention of producing a therapeutic effect. Medicines usually contain other substances (excipients, stabilisers, solvents, etc.) besides the active drug, to make them more convenient to use. To count as a drug, the substance must be administered as such, rather than released by physiological mechanisms. Many substances, such as insulin or thyroxine, are endogenous hormones but are also drugs when they are administered intentionally. Many drugs are not used in medicines but are nevertheless useful research tools. In everyday parlance, the word drug is often associated with addictive, narcotic or mind-altering substances-an unfortunate negative connotation that tends to bias opinion against any form of chemical therapy. In this book, we focus mainly on drugs used for therapeutic purposes but also describe important examples of drugs used as experimental tools.