Skip to Main Content


Pharmacology may be defined as the study of substances that interact with living systems through chemical processes, especially by binding to regulatory molecules and activating or inhibiting normal body processes. In this book, these substances will be referred to as drugs. Drugs are administered to achieve a beneficial therapeutic effect on some process within the patient or for their toxic effects on regulatory processes in organisms infecting the patient. Such deliberate therapeutic applications may be considered the proper role of pharmacotherapeutics, which is often defined as medical pharmacology (i.e., drugs used to prevent, diagnose, and treat diseases). Pharmacotherapeutics may be further subdivided into pharmacodynamics and pharmacokinetics. Pharmacodynamics evaluates the effect of the substance on biologic processes, and will be discussed in Chapter 2. Pharmacokinetics examines the absorption, distribution, and elimination of substances, and will be discussed in Chapter 3. Toxicology is the branch of pharmacology that deals with the undesirable effects of chemicals on living systems, from individual cells to complex ecosystems.


The use of substances for their medicinal value has occurred throughout history. Prehistoric people undoubtedly recognized the beneficial or toxic effects of many plant and animal materials. The earliest written records from China and Egypt list remedies of many types, including a few still recognized today as useful drugs. Most, however, were of limited clinical value or were actually harmful. Around the end of the 17th century, reliance on observation and experimentation began to replace theorizing in medicine. In the late 18th and early 19th centuries, methods for experimental animal physiology and advances in chemistry further increased the understanding of these chemical substances. This understanding resulted in the concept of drug selectivity, and that drugs may be grouped together into pharmacologic classes based on their physiologic effect or chemical structure. About 50 years ago, there began a major expansion of research efforts in all areas of biology. This expansion coincided with the development of controlled clinical trials that allowed accurate evaluation of the therapeutic value of drugs. As new concepts and new techniques were introduced, information accumulated about the action of drugs on the biologic substrate. During the last half century, many fundamentally new pharmacologic classes and new members of old classes were introduced.


The extension of scientific principles into everyday pharmacotherapeutics is still ongoing. Unfortunately, the drug-consuming public is still exposed to vast amounts of inaccurate, incomplete, or unscientific information regarding the pharmacologic effects of drugs. This has resulted in the faddish use of innumerable expensive, ineffective, and sometimes harmful remedies and the growth of a huge “alternative health-care” industry. Conversely, lack of understanding of basic scientific principles and the investigative process has led to rejection of medical science by a segment of the public, and a common tendency to assume that all adverse drug effects are the result of malpractice. Two general principles should form the basis of understanding for the evidence-based use of drugs. First, all substances may, under certain circumstances, be toxic. ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.


About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessPhysiotherapy Full Site: One-Year Subscription

Connect to the full suite of AccessPhysiotherapy content and resources including interactive NPTE review, more than 500 videos, Anatomy & Physiology Revealed, 20+ leading textbooks, and more.

$595 USD
Buy Now

Pay Per View: Timed Access to all of AccessPhysiotherapy

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.