1
GENERAL PRINCIPLES SECTION 1
What is pharmacology? 1
OVERVIEW
In this introductory chapter we explain how phar-
macology came into being and evolved as a scientific
discipline, and describe the present-day structure
of the subject and its links to other biomedical sciences.
The structure that has emerged forms the basis of
the organisation of the rest of the book. Readers in
a hurry to get to the here-and-now of pharmacology
can safely skip this chapter.
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,1 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 biotechnology (biopharmaceuticals). 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 commonly in
medicine but are nevertheless useful research tools. The
definition of drug also covers toxins, which again are not
usually administered in the clinic but nonetheless are critical
pharmacological tools. In everyday parlance, the word drug
is often associated with psychoactive substances and addic-
tion – unfortunate negative connotations that tend to bias
uninformed opinion against any form of chemical therapy.
In this book we focus mainly on drugs used for therapeutic
purposes but also describe psychoactive drugs and provide
important examples of drugs used as experimental tools.
Poisons fall strictly within the definition of drugs, and
indeed ‘all drugs are poisons… it is only the dose which
makes a thing poison’ (an aphorism credited to Paracelsus,
a 16th century Swiss physician); conversely, poisons may be
effective therapeutic agents when administered in sub-toxic
doses. Botulinum toxin (Ch. 14) provides a striking example:
it is the most potent poison known in terms of its lethal
dose, but is widely used both medically and cosmetically.
General aspects of harmful effects of drugs are considered
in Chapter 58. Toxicology is the study of toxic effects of
chemical substances (including drugs), and toxicological
testing is undertaken on new chemical entities during their
development as potential medicinal products (Ch. 60), but
the subject is not otherwise covered in this book.
ORIGINS AND ANTECEDENTS
Pharmacology can be defined as the study of the effects of
drugs on the function of living systems. As a science, it
was born in the mid-19th century, one of a host of new
biomedical sciences based on principles of experimentation
rather than dogma that came into being in that remarkable
period. Long before that – indeed from the dawn of civilisa-
tion – herbal remedies were widely used, pharmacopoeias
were written, and the apothecaries’ trade flourished.
However, nothing resembling scientific principles was
applied to therapeutics, which was known at that time as
materia medica.2 Even Robert Boyle, who laid the scientific
foundations of chemistry in the middle of the 17th century,
was content, when dealing with therapeutics (A Collection
of Choice Remedies, 1692), to recommend concoctions of
worms, dung, urine and the moss from a dead man’s skull.
The impetus for pharmacology came from the need to
improve the outcome of therapeutic intervention by doctors,
who were at that time skilled at clinical observation and
diagnosis but broadly ineffectual when it came to treatment.3
Until the late 19th century, knowledge of the normal and
abnormal functioning of the body was too rudimentary to
provide even a rough basis for understanding drug effects;
at the same time, disease and death were regarded as
semi-sacred subjects, appropriately dealt with by authoritar-
ian, rather than scientific, doctrines. Clinical practice often
displayed an obedience to authority and ignored what
appear to be easily ascertainable facts. For example, cinchona
bark was recognised as a specific and effective treatment
for malaria, and a sound protocol for its use was laid down
by Lind in 1765. In 1804, however, Johnson declared it to
be unsafe until the fever had subsided, and he recommended
instead the use of large doses of calomel (mercurous
chloride) in the early stages – a murderous piece of advice
that was slavishly followed for the next 40 years.
1Like most definitions, this one has its limits. For example, there are a
number of essential dietary constituents, such as iron and various
vitamins, that are used as medicines. Furthermore, some biological
products (e.g. epoietin) show batch-to-batch variation in their chemical
constitution that significantly affects their properties. There is also the
study of pharmaceutical-grade nutrients or ‘nutraceuticals’.
2The name persists today in some ancient universities, being attached to
chairs of what we would call clinical pharmacology.
3Oliver Wendell Holmes, an eminent physician, wrote in 1860: ‘[I]
firmly believe that if the whole materia medica, as now used, could be
sunk to the bottom of the sea, it would be all the better for mankind
and the worse for the fishes’ (see Porter, 1997).
