What is Pharmacology?: Definition, Basic Concept & Branches

Pharmacology is one of the most important subjects in the Pharmacy and medical field. Pharmacology is the cornerstone of modern pharmacy practice.

In this article, you will learn what is Pharmacology, Its basic concept, definition, what is a drug and how it works, what are the branches of pharmacology.

Let’s have a look;


What is Pharmacology?

The word pharmacology is derived from two Greek words, pharmacon meaning a “drug” and logy meaning “study.”

  • Pharmacology is the study of how medicinal substances interact with living systems.
  • Pharmacology is the branch of medical and pharmaceutical science that deals with the study of drugs, their nature, their sources, and their properties, absorption, distribution, biotransformation, elimination, interactions, toxicology, and therapeutic applications.
  • Pharmacology is the study of the body’s reaction to drugs.
  • Pharmacology is the study of Pharmacokinetics and Pharmacodynamics of a drug. These are also the two main areas of pharmacology.

Pharmacology looks at how drugs work (a mechanism), their side effects, and their interaction with other drugs in a broader sense.

Pharmacology is at the centre of biomedical science, combining chemistry, physiology, and pathology.

The person who is an expert in pharmacology is known as Pharmacologist. They work closely with several other fields that make modern biomedical sciences, including neuroscience, molecular and cellular biology, immunology, and cancer biology.

This subject explains what the drugs are, what they do for physiological functions, and what the body does with the drug.

Pharmacology also explains each drug’s dosage,  why a person may experience side effects when consuming drugs, and why there is such a broad view of the difference between drug actions among different people.

Pharmacology provides the research to understand the safety and efficacy of these drugs.

Pharmacology vs Pharmacy

As we have discussed above the Pharmacology is actually the branch of medical science in which we study the drugs research, discovery, the function of cellular and organic functions of these chemical products.

While Pharmacy is a health care professional and is the application of the principles learned from pharmacology.

Pharmacology vs Pharmacist

Pharmacology is a subject and discipline while Pharmacists is a person who formulates and dispenses medicine. Pharmacists study this in the doctor of pharmacy degree as a subject, and this is the basic and cornerstone of modern pharmacy practice.

To know what exactly is pharmacology, you need to understand the drug first.

What is a Drug?

Any chemical substance that is used for the diagnosis, prevention and treatment of diseases.


A drug is any chemical entity that causes a change in biological function in a living organism.

Some drugs are formed naturally inside the body, such as insulin and noradrenaline, etc. Drugs that are human-made or natural and introduced into the body from outside are called Xenobiotics. For example, are all those medicines such as paracetamol and all other drugs we take orally or on other routes?

How do drugs work?

Drugs generally work by interacting with receptors on the surface of cells or enzymes within cells. Receptor and enzyme molecules have a specific three-dimensional structure that allows only substances that precisely attach to them.

What is a Receptor?

A drug receptor is a specific target macromolecule that binds to a drug and mediates its pharmacological process. These receptors can be enzymes, nucleic acids, or proteins that are bound to special membranes.

The formation of drug-receptor complexes leads to biological reactions. The intensity of the reaction is proportional to the number of drug-receptor complexes. A common way to show the relationship between drug concentration and the biological response is to use a concentration or a dose-response curve.

Protein is present in many different forms in the body and has many different functions. Each protein has a specific function and is specific to the type of cell on which it functions.

For example, there are certain types of proteins called receptors. Receptors embed in cell surfaces; there are different receptors for different types of cells. Liver cells have different receptors than heart cells. The receptor binds to other proteins and chemicals outside the cell, which, in turn, changes how the cell functions.

Proteins also work on drug targets. For a drug to take effect, it must be protein-bound. It can be considered a lock and key system. Once the drug is attached to the receptor, it can have two important effects on the cell. It can produce a change in the response or stop a normal response from the cell.

If it produces a change in the response, this will be called agonist, and if it stops, it will be known as antagonists.

Dose-Response Curve

The concept of the dose-response curve is one of the most important concepts of pharmacology. A dose-response curve refers to the relationship between a drug’s effect and the amount of drug given.

The dose response curves relationship is important for understanding the drug’s safe and dangerous levels. The treatment index can be determined and dosing guidelines established.

The dose response curves are drawn on a simple x/y-axis, the drug dose is usually on the x-axis, and the drug response is usually on the y axis. Most are presented on a logometric scale as opposed to the curvature of the drug response. The Y-axis is often represented by a percentage to indicate the percentage of people who will respond to the drug. When reviewing dose response curves, an important feature of curves is that it is a graduated relationship. This means that the response of drug increase with the amount of drug administered. This classification of dose response curves allows your doctor to adapt the person taking the drug to the prescription.

If you increase the dose, the response will also be increased, but at a certain level, the effect and the curve plateau at the top will stop even if you further increase the dose.  This is the point where your body’s ability to detoxify a drug or repair toxic injury has been exceeded.

Effective Dose Vs Lethal Dose

The effective dose (ED50) is the amount of drug that shows a biological response in the body while the Lethal dose (LD50) is the amount of a drug or toxin that causes death in 50% of the test animals. [1]

⇒ What are potency and efficacy?

The drug’s potency means the dose of a drug that shows 50% of the effect, while the efficacy is the dose of a drug by which it shows a response.

  • The potency is the concentration or dose of a drug required to produce 50% of that drug’s maximal effect.
  • Efficacy is the maximum effect expected from a drug (i.e., when this magnitude of the effect is reached, increasing the dose will not produce a greater effect).
  • For example, one medication (med A) treats disease at a dose of 10 mg. A subsequent medication (Med B) treat that disease at a dose of 20 mg. In this manner, the two medications have similar efficacy, yet “Med A” is more potent than drug B. It takes less of medication A to create a similar impact.

⇒ What is a first-pass effect?

This is one of the most commonly used terms among pharmacist and pharmacy students, and many Pharmacy students are confused about this terminology.

Your liver is actually a metabolic machine, and it often inactivates drugs on their way from the gastric Intestinal tract to the body. This is called the first-pass effect.

There are other concepts about pharmacology, like what is pharmacokinetics and pharmacodynamics?

Branches of Pharmacology

Following are the important branches of Pharmacology:

Pharmacology has 2 main branches.

  • Pharmacodynamics
  • Pharmacokinetics

Other branches of pharmacology include

  • Therapeutics
  • Clinical Pharmacology
  • Pharmacogenetics
  • Pharmacognosy
  • Toxicology
  • Pharmacoepidemiology
  • Animal Pharmacology
  • Posology
  • Pharmacoeconomics
  • Chemotherapy
  • Comparative Pharmacology
  • Neuropharmacology
  • Psychopharmacology
  • Cardiovascular pharmacology
  • Pharmacovigilance

1. Pharmacokinetics

Pharmacokinetics refers to the movement of drugs inside, through, and on the body. The nature of an individual’s response to a particular drug depends on the drug’s intrinsic pharmacological properties at its site of action.

Pharmacokinetics investigates how the body absorbs, metabolizes, and excretes drugs.

A drug can be administered orally, parenterally (for example, by injection), or intravenously.

The kidney is the main organ that filters drugs out of the body, but also the lungs and sweat glands play a minor role.

However, the rate of occurrence, intensity, and duration of the response generally depends on the following parameters:

  • The rate and extent of drug absorption.
  • The rate and extent of distribution of the drug in different tissues, including the site of action;
  • The rate of excretion of the drug from the body.
2. Pharmacodynamics

Pharmacodynamics is defined as the body’s response to the drug. It refers to the relationship between the drug concentration at the site of action and any effect, namely the intensity and the time course of the effect and the side effects.

Pharmacodynamics is influenced by receptor binding and sensitivity, post-receptor effects, and chemical interactions.

Pharmacodynamics and pharmacokinetics explain the effects of the drug, such as the relationship between dose and response.

The pharmacological response depends on the binding of the drug to its target. The concentration of the drug at the receptor site influences its effect.

The pharmacodynamics of a drug may be influenced by physiological changes due to diseases, genetic mutations, ageing, or other drugs. These changes are due to the disorders’ ability to modify receptor binding, alter the number of binding proteins, or decrease the receptor’s sensitivity.

3. Chemotherapy

Chemotherapy is the pharmacology field that deals with the medicines used to treat cancer and malignancies with cytotoxic and other drugs.

4.  Therapeutics

Therapy is the branch of pharmacology specialized in treating diseases and in the art and science of healing. Therefore, in pharmacology, the treatments refer to drugs and their administration method to treat diseases.

5. Clinical Pharmacology

Clinical pharmacology promotes the rational use of drugs in humans by examining their corrective effects to increase the drug’s effect and reduce side effects.

This is pharmacology with an added emphasis on applying pharmacological principles and methods in the real world. This ranges from the discovery of new target molecules to the effects of drug use in the population.

6. Pharmacogenetics

Pharmacogenetic is the study of variability in drug response due to heredity. It is the study of the role of the genome in drug response. Pharmacogenomics analyzes how the genetic composition of an individual influences their response to medication.

7. Pharmacognosy

Pharmacognosy is the study of drugs derived from natural sources. This deals with the pharmacodynamics and the mechanisms by which substances, mainly from natural sources, directly or indirectly influence living systems changes.

8. Toxicology

Toxicology is a branch of pharmacology devoted to the scientific study of the harmful effects of drugs on living organisms. This involves observing and reporting the symptoms, mechanisms, detection, and treatment of toxic substances, particularly in humans’ poisoning.

Includes environmental agents and natural chemical compounds, as well as synthesized pharmaceutical compounds for medical use. These substances can have toxic effects on living organisms, including growth disorders, discomfort, illness, and death.

9. Pharmacoepidemiology

Pharmacoepidemiology is the branch of pharmacology that deals with studying the use and effects of drugs in many people. It provides an estimate of the likelihood of a drug’s beneficial effects in a population and its adverse effects. This can be called a bridge science that encompasses both clinical pharmacology and epidemiology.

10. Animal Pharmacology

Animal pharmacology deals with the different properties of drugs in animals. A wide variety of animals are used, including rabbits, mice, guinea pigs, etc. The drugs are administered to the animals, and all the parameters (behaviour, activity, vital signs, etc.) are recorded. Each change is noted below. If it is useful in animals, the drug is tested in humans.

11. Posology

It is the branch of pharmacology and the therapies concern with determining the doses of the remedies; It is the science of dosage. For example, ibuprofen’s usual dose in adults and adolescents over 12 years is 200 mg to 400 mg three to four times a day.

12 Pharmacoeconomics

Pharmacoeconomics is the scientific discipline that concerns the cost and value of drugs, often intending to optimize health resource allocation. For example, pharmacoeconomic studies can compare the costs of various drugs with results, such as the benefits for patients receiving drugs and the savings made by health systems through effective treatment or disease prevention.

13. Comparative pharmacology

It is a pharmacology branch that compares one drug to another, belonging to the same group or the other.

14. Neuropharmacology

Neuropharmacology is a branch of neuroscience that studies the effects of drugs on the nervous system, including the brain, spinal cord, and nerves that carry information to and from different parts of the body. The goal of neuropharmacology, in general, is to understand the basic function of impulses and signals in the brain to determine the effects of drugs on the treatment of neurological disorders and dependence.

15. Psychopharmacology

Psychopharmacology is the scientific study of the effects of drugs on mood, sensation, reflection, and behaviour. It is distinct from neuropsychopharmacology, which focuses on the correlation between drug-induced nervous system function changes and changes in consciousness and behaviour.

16. Cardiovascular pharmacology

Cardiovascular pharmacology is the study of the effects of drugs on the entire cardiovascular system. Cardiovascular Relative to the circulatory system, which includes the heart and blood vessels, transports nutrients and oxygen to body tissues and removes carbon dioxide and other wastes. Cardiovascular diseases are disorders of the heart and blood vessels. They include arteriosclerosis, coronary artery disease, heart valve arrhythmia, arrhythmia, heart failure, hypertension, orthostatic hypotension, shock, endocarditis, diseases of the aorta and its branches, disorders of the peripheral vascular system, and congenital heart disease.

17. Pharmacovigilance

According to the World Health Organization,  “Science and activities related to the identification, evaluation, understanding, and prevention of adverse effects or any other possible problem related to drugs.”

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This Article is Written & Reviewed By A Registered Pharmacist: Manzoor Ahmad


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