Pharmacology is the branch of biology concerned with the study of drug action,[1] where a drug can be broadly defined as any man-made, natural, or endogenous (from within the body) molecule which exerts a biochemical or physiological effect on the cell, tissue, organ, or organism (sometimes the word pharmacon is used as a term to encompass these endogenous and exogenous bioactive species). More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function. If substances have medicinal properties, they are considered pharmaceuticals.

The field encompasses drug composition and properties, synthesis and drug design, molecular and cellular mechanisms, organ/systems mechanisms, signal transduction/cellular communication, molecular diagnostics, interactions, toxicology, chemical biology, therapy, and medical applications and antipathogenic capabilities. The two main areas of pharmacology are pharmacodynamics and pharmacokinetics. Pharmacodynamics studies the effects of a drug on biological systems, and Pharmacokinetics studies the effects of biological systems on a drug. In broad terms, pharmacodynamics discusses the chemicals with biological receptors, and pharmacokinetics discusses the absorption, distribution, metabolism, and excretion (ADME) of chemicals from the biological systems. Pharmacology is not synonymous with pharmacy and the two terms are frequently confused. Pharmacology, a biomedical science, deals with the research, discovery, and characterization of chemicals which show biological effects and the elucidation of cellular and organismal function in relation to these chemicals. In contrast, pharmacy, a health services profession, is concerned with application of the principles learned from pharmacology in its clinical settings; whether it be in a dispensing or clinical care role. In either field, the primary contrast between the two are their distinctions between direct-patient care, for pharmacy practice, and the science-oriented research field, driven by pharmacology.

The origins of clinical pharmacology date back to the Middle Ages in Avicenna's The Canon of Medicine, Peter of Spain's Commentary on Isaac, and John of St Amand's Commentary on the Antedotary of Nicholas.[2] Clinical pharmacology owes much of its foundation to the work of William Withering.[3] Pharmacology as a scientific discipline did not further advance until the mid-19th century amid the great biomedical resurgence of that period.[4] Before the second half of the nineteenth century, the remarkable potency and specificity of the actions of drugs such as morphine, quinine and digitalis were explained vaguely and with reference to extraordinary chemical powers and affinities to certain organs or tissues.[5] The first pharmacology department was set up by Rudolf Buchheim in 1847, in recognition of the need to understand how therapeutic drugs and poisons produced their effects.[4]

Early pharmacologists focused on natural substances, mainly plant extracts. Pharmacology developed in the 19th century as a biomedical science that applied the principles of scientific experimentation to therapeutic contexts.[6] Today pharmacologists use genetics, molecular biology, biochemistry, and other advanced tools to transform information about molecular mechanisms and targets into therapies directed against disease, defects or pathogens, and create methods for preventative care, diagnostics, and ultimately personalized medicine.

Constant tempertature bath for isolated organs Wellcome M0013241
Diagrammatic representation of organ bath used for studying the effect of isolated tissues
MeSH Unique IDD010600


The word "pharmacology" is derived from Greek φάρμακον, pharmakon, "drug, poison, spell" and -λογία, -logia "study of", "knowledge of"[7][8] (cf. the etymology of pharmacy).


A variety of topics involved with pharmacology, including neuropharmacology, renal pharmacology, human metabolism, intracellular metabolism, and intracellular regulation

The discipline of pharmacology can be divided into many sub disciplines each with a specific focus.

Clinical pharmacology

Clinical pharmacology is the basic science of pharmacology with an added focus on the application of pharmacological principles and methods in the medical clinic and towards patient care and outcomes.


Neuropharmacology is the study of the effects of medication on central and peripheral nervous system functioning.


Psychopharmacology, also known as behavioral pharmacology, is the study of the effects of medication on the psyche (psychology), observing changed behaviors of the body and mind, and how molecular events are manifest in a measurable behavioral form. Psychopharmacology is an interdisciplinary field which studies behavioral effects of psychoactive drugs. It incorporates approaches and techniques from neuropharmacology, animal behavior and behavioral neuroscience, and is interested in the behavioral and neurobiological mechanisms of action of psychoactive drugs. Another goal of behavioral pharmacology is to develop animal behavioral models to screen chemical compounds with therapeutic potentials. People in this field (called behavioral pharmacologists) typically use small animals (e.g. rodents) to study psychotherapeutic drugs such as antipsychotics, antidepressants and anxiolytics, and drugs of abuse such as nicotine, cocaine and methamphetamine. Ethopharmacology (not to be confused with ethnopharmacology) is a term which has been in use since the 1960s[9] and derives from the Greek word ἦθος ethos meaning character and "pharmacology" the study of drug actions and mechanism.

Cardiovascular pharmacology

Cardiovascular pharmacology is the study of the effects of drugs on the entire cardiovascular system, including the heart and blood vessels.


Pharmacogenetics is clinical testing of genetic variation that gives rise to differing response to drugs.


Pharmacogenomics is the application of genomic technologies to drug discovery and further characterization of older drugs.


Pharmacoepidemiology is the study of the effects of drugs in large numbers of people.

Safety pharmacology

Safety pharmacology specialises in detecting and investigating potential undesirable pharmacodynamic effects of new chemical entities (NCEs) on physiological functions in relation to exposure in the therapeutic range and above.

Systems pharmacology

Systems pharmacology is the application of systems biology principles in the field of pharmacology.


Toxicology is the study of the adverse effects, molecular targets, and characterization of drugs or any chemical substance in excess (including those beneficial in lower doses).

Theoretical pharmacology

Theoretical pharmacology is a relatively new and rapidly expanding field of research activity in which many of the techniques of computational chemistry, in particular computational quantum chemistry and the method of molecular mechanics, are proving to be of great value. Theoretical pharmacologists aim at rationalizing the relation between the activity of a particular drug, as observed experimentally, and its structural features as derived from computer experiments. They aim to find structure—activity relations. Furthermore, on the basis of the structure of a given organic molecule, the theoretical pharmacologist aims at predicting the biological activity of new drugs that are of the same general type as existing drugs. More ambitiously, it aims to predict entirely new classes of drugs, tailor-made for specific purposes.


Posology is the study of how medicines are dosed. This depends upon various factors including age, climate, weight, sex, elimination rate of drug, genetic polymorphism and time of administration. It is derived from the Greek words πόσος posos meaning "how much?" and -λογία -logia "study of".[10]

Environmental pharmacology

Environmental pharmacology is a new discipline.[11] Focus is being given to understand gene–environment interaction, drug-environment interaction and toxin-environment interaction. There is a close collaboration between environmental science and medicine in addressing these issues, as healthcare itself can be a cause of environmental damage or remediation. Human health and ecology are intimately related. Demand for more pharmaceutical products may place the public at risk through the destruction of species. The entry of chemicals and drugs into the aquatic ecosystem is a more serious concern today. In addition, the production of some illegal drugs pollutes drinking water supply by releasing carcinogens.[12] This field is intimately linked with Public Health fields.

Experimental pharmacology

Experimental pharmacology involves the study of pharmacology through bioassay, to test the efficacy and potency of a drug.

Scientific background

The study of chemicals requires intimate knowledge of the biological system affected. With the knowledge of cell biology and biochemistry increasing, the field of pharmacology has also changed substantially. It has become possible, through molecular analysis of receptors, to design chemicals that act on specific cellular signaling or metabolic pathways by affecting sites directly on cell-surface receptors (which modulate and mediate cellular signaling pathways controlling cellular function).

A chemical has, from the pharmacological point-of-view, various properties. Pharmacokinetics describes the effect of the body on the chemical (e.g. half-life and volume of distribution), and pharmacodynamics describes the chemical's effect on the body (desired or toxic).

When describing the pharmacokinetic properties of the chemical that is the active ingredient or active pharmaceutical ingredient (API), pharmacologists are often interested in L-ADME:

  • Liberation – How is the API disintegrated (for solid oral forms (breaking down into smaller particles)), dispersed, or dissolved from the medication?
  • Absorption – How is the API absorbed (through the skin, the intestine, the oral mucosa)?
  • Distribution – How does the API spread through the organism?
  • Metabolism – Is the API converted chemically inside the body, and into which substances. Are these active (as well)? Could they be toxic?
  • Excretion – How is the API excreted (through the bile, urine, breath, skin)?

Medication is said to have a narrow or wide therapeutic index or therapeutic window. This describes the ratio of desired effect to toxic effect. A compound with a narrow therapeutic index (close to one) exerts its desired effect at a dose close to its toxic dose. A compound with a wide therapeutic index (greater than five) exerts its desired effect at a dose substantially below its toxic dose. Those with a narrow margin are more difficult to dose and administer, and may require therapeutic drug monitoring (examples are warfarin, some antiepileptics, aminoglycoside antibiotics). Most anti-cancer drugs have a narrow therapeutic margin: toxic side-effects are almost always encountered at doses used to kill tumors.

Medicine development and safety testing

Development of medication is a vital concern to medicine, but also has strong economical and political implications. To protect the consumer and prevent abuse, many governments regulate the manufacture, sale, and administration of medication. In the United States, the main body that regulates pharmaceuticals is the Food and Drug Administration and they enforce standards set by the United States Pharmacopoeia. In the European Union, the main body that regulates pharmaceuticals is the EMA and they enforce standards set by the European Pharmacopoeia.

The metabolic stability and the reactivity of a library of candidate drug compounds have to be assessed for drug metabolism and toxicological studies. Many methods have been proposed for quantitative predictions in drug metabolism; one example of a recent computational method is SPORCalc.[13] If the chemical structure of a medicinal compound is altered slightly, this could slightly or dramatically alter the medicinal properties of the compound depending on the level of alteration as it relates to the structural composition of the substrate or receptor site on which it exerts its medicinal effect, a concept referred to as the structural activity relationship (SAR). This means that when a useful activity has been identified, chemists will make many similar compounds called analogues, in an attempt to maximize the desired medicinal effect(s) of the compound. This development phase can take anywhere from a few years to a decade or more and is very expensive.[14]

These new analogues need to be developed. It needs to be determined how safe the medicine is for human consumption, its stability in the human body and the best form for delivery to the desired organ system, like tablet or aerosol. After extensive testing, which can take up to 6 years, the new medicine is ready for marketing and selling.[14]

As a result of the long time required to develop analogues and test a new medicine and the fact that of every 5000 potential new medicines typically only one will ever reach the open market, this is an expensive way of doing things, often costing over 1 billion dollars. To recoup this outlay pharmaceutical companies may do a number of things:[14]

  • Carefully research the demand for their potential new product before spending an outlay of company funds.[14]
  • Obtain a patent on the new medicine preventing other companies from producing that medicine for a certain allocation of time.[14]

Drug legislation and safety

In the United States, the Food and Drug Administration (FDA) is responsible for creating guidelines for the approval and use of drugs. The FDA requires that all approved drugs fulfill two requirements:

  1. The drug must be found to be effective against the disease for which it is seeking approval (where 'effective' means only that the drug performed better than placebo or competitors in at least two trials).
  2. The drug must meet safety criteria by being subject to animal and controlled human testing.

Gaining FDA approval usually takes several years. Testing done on animals must be extensive and must include several species to help in the evaluation of both the effectiveness and toxicity of the drug. The dosage of any drug approved for use is intended to fall within a range in which the drug produces a therapeutic effect or desired outcome.[15]

The safety and effectiveness of prescription drugs in the U.S. is regulated by the federal Prescription Drug Marketing Act of 1987.

The Medicines and Healthcare products Regulatory Agency (MHRA) has a similar role in the UK.


Students of pharmacology are trained as biomedical scientists, studying the effects of drugs on living organisms. This can lead to new drug discoveries, as well as a better understanding of the way in which the human body works.

Students of pharmacology must have detailed working knowledge of aspects in physiology, pathology and chemistry. During a typical degree they will cover areas such as (but not limited to) biochemistry, cell biology, basic physiology, genetics and the Central Dogma, medical microbiology, neuroscience, and depending on the department's interests, bio-organic chemistry, or chemical biology.

Modern Pharmacology is highly interdisciplinary. Graduate programs accept students from most biological and chemical backgrounds. With the increasing drive towards biophysical and computational research to describe systems, pharmacologists may even consider themselves mainly physical scientists. In many instances, Analytical Chemistry is closely related to the studies and needs of pharmacological research. Therefore, many institutions will include pharmacology under a Chemistry or Biochemistry Department, especially if a separate Pharmacology Dept. does not exist. What makes an institutional department independent of another, or exist in the first place, is usually an artifact of historical times.[16]

Whereas a pharmacy student will eventually work in a pharmacy dispensing medications, a pharmacologist will typically work within a laboratory setting. Careers for a pharmacologist include academic positions (medical and non-medical), governmental positions, private industrial positions, science writing, scientific patents and law, consultation, biotech and pharmaceutical employment, the alcohol industry, food industry, forensics/law enforcement, public health, and environmental/ecological sciences.

See also


  1. ^ Vallance P, Smart TG (January 2006). "The future of pharmacology". British Journal of Pharmacology. 147 Suppl 1 (S1): S304–7. doi:10.1038/sj.bjp.0706454. PMC 1760753. PMID 16402118.
  2. ^ Brater DC, Daly WJ (May 2000). "Clinical pharmacology in the Middle Ages: principles that presage the 21st century". Clin. Pharmacol. Ther. 67 (5): 447–50. doi:10.1067/mcp.2000.106465. PMID 10824622.
  3. ^ Mannfred A. Hollinger (2003)."Introduction to pharmacology". CRC Press. p.4. ISBN 0-415-28033-8
  4. ^ a b Rang HP (January 2006). "The receptor concept: pharmacology's big idea". Br. J. Pharmacol. 147 Suppl 1 (S1): S9–16. doi:10.1038/sj.bjp.0706457. PMC 1760743. PMID 16402126.
  5. ^ Maehle AH, Prüll CR, Halliwell RF (August 2002). "The emergence of the drug receptor theory". Nat Rev Drug Discov. 1 (8): 637–41. doi:10.1038/nrd875. PMID 12402503.
  6. ^ Rang, H.P.; M.M. Dale; J.M. Ritter; R.J. Flower (2007). Pharmacology. China: Elsevier. ISBN 0-443-06911-5.
  7. ^ Pharmacy (n.) - Online Etymology Dictionary
  8. ^ Pharmacology - Online Etymology Dictionary
  9. ^ Krsiak, M (1991). "Ethopharmacology: A historical perspective". Neuroscience and Biobehavioral Reviews. 15 (4): 439–45. doi:10.1016/s0149-7634(05)80124-1. PMID 1792005.
  10. ^ "posology". Random House Webster's Unabridged Dictionary.
  11. ^ Rahman, SZ; Khan, RA (December 2006). "Environmental pharmacology: A new discipline". Indian J. Pharmacol. 38 (4): 229–30. doi:10.4103/0253-7613.27017.
  12. ^ Sue Ruhoy Ilene; Daughton Christian G (2008). "Beyond the medicine cabinet: An analysis of where and why medications accumulate". Environment International. 34 (8): 1157–1169. doi:10.1016/j.envint.2008.05.002.
  13. ^ James Smith; Viktor Stein (2009). "SPORCalc: A development of a database analysis that provides putative metabolic enzyme reactions for ligand-based drug design". Computational Biology and Chemistry. 33 (2): 149–159. doi:10.1016/j.compbiolchem.2008.11.002. PMID 19157988.
  14. ^ a b c d e Newton, David; Alasdair Thorpe; Chris Otter (2004). Revise A2 Chemistry. Heinemann Educational Publishers. p. 1. ISBN 0-435-58347-6.
  15. ^ Nagle, Hinter; Barbara Nagle (2005). Pharmacology: An Introduction. Boston: McGraw Hill. ISBN 0-07-312275-0.
  16. ^ "Examinations In Pharmacology". The British Medical Journal. 1 (1833): 418–418. 1896. JSTOR 20234917.

External links

BioMed Central

BioMed Central (BMC) is a United Kingdom-based, for-profit scientific open access publisher. BioMed Central publishes over 250 scientific journals. All BioMed Central journals are only published online. BioMed Central describes itself as the first and largest open access science publisher. It is owned by Springer Nature.


In pharmacology, bioavailability (BA or F) is a subcategory of absorption and is the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered intravenously, its bioavailability is 100%. However, when a medication is administered via other routes (such as orally), its bioavailability generally decreases (due to incomplete absorption and first-pass metabolism) or may vary from patient to patient. Bioavailability is one of the essential tools in pharmacokinetics, as bioavailability must be considered when calculating dosages for non-intravenous routes of administration.

For dietary supplements, herbs and other nutrients in which the route of administration is nearly always oral, bioavailability generally designates simply the quantity or fraction of the ingested dose that is absorbed.Bioavailability is defined slightly differently for drugs as opposed to dietary supplements primarily due to the method of administration and Food and Drug Administration regulations.

Clinical pharmacology

Clinical pharmacology is the science of drugs in humans and their optimal clinical use in patients. It is underpinned by the basic science of pharmacology, with an added focus on the application of pharmacological principles and quantitative methods in the real human patient's population. It has a broad scope, from the discovery of new target molecules to the effects of drug usage in whole populations.Clinical pharmacologists usually have a rigorous medical and scientific training that enables them to evaluate evidence and produce new data through well-designed studies. Clinical pharmacologists must have access to enough outpatients for clinical care, teaching and education, and research as well as be supervised by medical specialists. Their responsibilities to patients include, but are not limited to, analyzing adverse drug effects, therapeutics, and toxicology including reproductive toxicology, cardiovascular risks, perioperative drug management and psychopharmacology.

Clinical pharmacology also connects the gap between medical practice and laboratory science. The main objective is to promote the safety of prescription, maximize the drug effects and minimize the side effects. In this aspect, there can be an association with pharmacists skilled in areas of drug information, medication safety and other aspects of pharmacy practice related to clinical pharmacology. In fact, in countries such as USA, Netherlands, and France, pharmacists can be trained to become clinical pharmacists, to improve optimal drug therapy with clinical pharmacology related knowledge.

In addition, the application of genetic, biochemical, or virotherapeutic techniques has led to a clear appreciation of the mechanisms involved in drug action.

A bachelor's degree, in a clinical, health science or bioscience related field is typically required for enrollment on a master's degree level course in pharmacology. Institutions may also hold specific coursework and credit requirements for enrollment on advanced degrees in pharmacology.

Computational biology

Computational biology involves the development and application of data-analytical and theoretical methods, mathematical modeling and computational simulation techniques to the study of biological, ecological, behavioral, and social systems. The field is broadly defined and includes foundations in biology, applied mathematics, statistics, biochemistry, chemistry, biophysics, molecular biology, genetics, genomics, computer science and evolution.Computational biology is different from biological computing, which is a subfield of computer science and computer engineering using bioengineering and biology to build computers, but is similar to bioinformatics, which is an interdisciplinary science using computers to store and process biological data.

Drug metabolism

Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, such as any drug or poison. These pathways are a form of biotransformation present in all major groups of organisms, and are considered to be of ancient origin. These reactions often act to detoxify poisonous compounds (although in some cases the intermediates in xenobiotic metabolism can themselves cause toxic effects). The study of drug metabolism is called pharmacokinetics.

The metabolism of pharmaceutical drugs is an important aspect of pharmacology and medicine. For example, the rate of metabolism determines the duration and intensity of a drug's pharmacologic action. Drug metabolism also affects multidrug resistance in infectious diseases and in chemotherapy for cancer, and the actions of some drugs as substrates or inhibitors of enzymes involved in xenobiotic metabolism are a common reason for hazardous drug interactions. These pathways are also important in environmental science, with the xenobiotic metabolism of microorganisms determining whether a pollutant will be broken down during bioremediation, or persist in the environment. The enzymes of xenobiotic metabolism, particularly the glutathione S-transferases are also important in agriculture, since they may produce resistance to pesticides and herbicides.

Drug metabolism is divided into three phases. In phase I, enzymes such as cytochrome P450 oxidases introduce reactive or polar groups into xenobiotics. These modified compounds are then conjugated to polar compounds in phase II reactions. These reactions are catalysed by transferase enzymes such as glutathione S-transferases. Finally, in phase III, the conjugated xenobiotics may be further processed, before being recognised by efflux transporters and pumped out of cells. Drug metabolism often converts lipophilic compounds into hydrophilic products that are more readily excreted.


Efaroxan is an α2-adrenergic receptor antagonist and antagonist of the imidazoline receptor.


Efficacy is the ability to get a job done satisfactorily. The word comes from the same roots as effectiveness, and it has often been used synonymously, although in pharmacology a distinction is now often made between efficacy and effectiveness. The word efficacy is used in pharmacology and medicine to refer both to the maximum response achievable from a pharmaceutical drug in research settings, and to the capacity for sufficient therapeutic effect or beneficial change in clinical settings.

Guide to Pharmacology

The IUPHAR/BPS Guide to PHARMACOLOGY is an open-access website, acting as a portal to information on the biological targets of licensed drugs and other small molecules. The Guide to PHARMACOLOGY (with GtoPdb being the standard abbreviation) is developed as a joint venture between the International Union of Basic and Clinical Pharmacology (IUPHAR) and the British Pharmacological Society (BPS). This replaces and expands upon the original 2009 IUPHAR Database (standard abbreviation IUPHAR-DB) . The Guide to PHARMACOLOGY aims to provide a concise overview of all pharmacological targets, accessible to all members of the scientific and clinical communities and the interested public, with links to details on a selected set of targets. The information featured includes pharmacological data, target and gene nomenclature, as well as curated chemical information for ligands. Overviews and commentaries on each target family are included, with links to key references.

International Union of Basic and Clinical Pharmacology

The International Union of Basic and Clinical Pharmacology (IUPHAR) is a voluntary, non-profit association representing the interests of scientists in pharmacology-related fields to facilitate Better Medicines through Global Education and Research around the world.

Ligand (biochemistry)

In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In protein-ligand binding, the ligand is usually a molecule which produces a signal by binding to a site on a target protein. The binding typically results in a change of conformational isomerism (conformation) of the target protein. In DNA-ligand binding studies, the ligand can be a small molecule, ion, or protein which binds to the DNA double helix. The relationship between ligand and binding partner is a function of charge, hydrophobicity, and molecular structure. The instance of binding occurs over an infinitesimal range of time and space, so the rate constant is usually a very small number.

Binding occurs by intermolecular forces, such as ionic bonds, hydrogen bonds and Van der Waals forces. The association of docking is actually reversible through dissociation. Measurably irreversible covalent bonding between a ligand and target molecule is atypical in biological systems. In contrast to the definition of ligand in metalorganic and inorganic chemistry, in biochemistry it is ambiguous whether the ligand generally binds at a metal site, as is the case in hemoglobin. In general, the interpretation of ligand is contextual with regards to what sort of binding has been observed. The etymology stems from ligare, which means 'to bind'.

Ligand binding to a receptor protein alters the conformation by affecting the three-dimensional shape orientation. The conformation of a receptor protein composes the functional state. Ligands include substrates, inhibitors, activators, and neurotransmitters. The rate of binding is called affinity, and this measurement typifies a tendency or strength of the effect. Binding affinity is actualized not only by host–guest interactions, but also by solvent effects that can play a dominant, steric role which drives non-covalent binding in solution. The solvent provides a chemical environment for the ligand and receptor to adapt, and thus accept or reject each other as partners.

Radioligands are radioisotope labeled compounds used in vivo as tracers in PET studies and for in vitro binding studies.

Lithium (medication)

Lithium compounds, also known as lithium salts, are primarily used as a psychiatric medication. This includes the treatment of major depressive disorder that does not improve following the use of other antidepressants, and bipolar disorder. In these disorders, it reduces the risk of suicide. Lithium is taken by mouth.Common side effects include increased urination, shakiness of the hands, and increased thirst. Serious side effects include hypothyroidism, diabetes insipidus, and lithium toxicity. Blood level monitoring is recommended to decrease the risk of potential toxicity. If levels become too high, diarrhea, vomiting, poor coordination, sleepiness, and ringing in the ears may occur. If used during pregnancy, lithium can cause problems in the baby. It appears to be safe to use while breastfeeding. Lithium salts are classified as mood stabilizers. How lithium works is not specifically known.In the nineteenth century, lithium was used in people who had gout, epilepsy, and cancer. Its use in the treatment of mental disorder began in 1948 by John Cade in Australia. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. It is available as a generic medication. The wholesale cost in the developing world in 2014 was between 0.12 and 0.20 USD per day. In the United States at usual doses it costs about 0.90 to 1.20 USD per day. In 2016 it was the 222nd most prescribed medication in the United States with more than 2 million prescriptions.


A medication (also referred to as medicine, pharmaceutical drug, or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and relies on the science of pharmacology for continual advancement and on pharmacy for appropriate management.

Drugs are classified in various ways. One of the key divisions is by level of control, which distinguishes prescription drugs (those that a pharmacist dispenses only on the order of a physician, physician assistant, or qualified nurse) from over-the-counter drugs (those that consumers can order for themselves). Another key distinction is between traditional small-molecule drugs, usually derived from chemical synthesis, and biopharmaceuticals, which include recombinant proteins, vaccines, blood products used therapeutically (such as IVIG), gene therapy, monoclonal antibodies and cell therapy (for instance, stem-cell therapies). Other ways to classify medicines are by mode of action, route of administration, biological system affected, or therapeutic effects. An elaborate and widely used classification system is the Anatomical Therapeutic Chemical Classification System (ATC system). The World Health Organization keeps a list of essential medicines.

Drug discovery and drug development are complex and expensive endeavors undertaken by pharmaceutical companies, academic scientists, and governments. As a result of this complex path from discovery to commercialization, partnering has become a standard practice for advancing drug candidates through development pipelines. Governments generally regulate what drugs can be marketed, how drugs are marketed, and in some jurisdictions, drug pricing. Controversies have arisen over drug pricing and disposal of used drugs.

Partial agonist

In pharmacology, partial agonists are drugs that bind to and activate a given receptor, but have only partial efficacy at the receptor relative to a full agonist. They may also be considered ligands which display both agonistic and antagonistic effects—when both a full agonist and partial agonist are present, the partial agonist actually acts as a competitive antagonist, competing with the full agonist for receptor occupancy and producing a net decrease in the receptor activation observed with the full agonist alone. Clinically, partial agonists can be used to activate receptors to give a desired submaximal response when inadequate amounts of the endogenous ligand are present, or they can reduce the overstimulation of receptors when excess amounts of the endogenous ligand are present.Some currently common drugs that have been classed as partial agonists at particular receptors include buspirone, aripiprazole, buprenorphine, nalmefene and norclozapine. Examples of ligands activating peroxisome proliferator-activated receptor gamma as partial agonists are honokiol and falcarindiol. Delta 9-tetrahydrocannabivarin (THCV) is a partial agonist at CB2 receptors and this activity might be implicated in ∆9-THCV-mediated anti-inflammatory effects.

Potency (pharmacology)

In the field of pharmacology, potency is a measure of drug activity expressed in terms of the amount required to produce an effect of given intensity. A highly potent drug (e.g., fentanyl, alprazolam, risperidone) evokes a given response at low concentrations, while a drug of lower potency (meperidine, diazepam, ziprasidone) evokes the same response only at higher concentrations. Higher potency does not necessarily mean more side effects.

The IUPHAR has stated that 'potency' is "an imprecise term that should always be further defined", for instance as EC 50 {\displaystyle {\ce {EC_{50}}}} , IC 50 {\displaystyle {\ce {IC_{50}}}} , ED50, LD50 and so on.

Protease inhibitor (pharmacology)

Protease inhibitors (PIs) are a class of antiviral drugs that are widely used to treat HIV/AIDS and hepatitis C. Protease inhibitors prevent viral replication by selectively binding to viral proteases (e.g. HIV-1 protease) and blocking proteolytic cleavage of protein precursors that are necessary for the production of infectious viral particles.

Protease inhibitors that have been developed and are currently used in clinical practice include:

Given the specificity of the target of these drugs there is the risk, as in antibiotics, of the development of drug-resistant mutated viruses. To reduce this risk it is common to use several different drugs together that are each aimed at different targets.

Receptor antagonist

A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist. They are sometimes called blockers; examples include alpha blockers, beta blockers, and calcium channel blockers. In pharmacology, antagonists have affinity but no efficacy for their cognate receptors, and binding will disrupt the interaction and inhibit the function of an agonist or inverse agonist at receptors. Antagonists mediate their effects by binding to the active site or to the allosteric site on a receptor, or they may interact at unique binding sites not normally involved in the biological regulation of the receptor's activity. Antagonist activity may be reversible or irreversible depending on the longevity of the antagonist–receptor complex, which, in turn, depends on the nature of antagonist–receptor binding. The majority of drug antagonists achieve their potency by competing with endogenous ligands or substrates at structurally defined binding sites on receptors.

Receptor modulator

A receptor modulator, or receptor ligand, is a type of drug which binds to and modulates receptors. They are ligands and include receptor agonists and receptor antagonists, as well as receptor partial agonists, inverse agonists, and allosteric modulators.

Science in the medieval Islamic world

Science in the medieval Islamic world was the science developed and practised during the Islamic Golden Age under the Umayyads of Córdoba, the Abbadids of Seville, the Samanids, the Ziyarids, the Buyids in Persia, the Abbasid Caliphate and beyond, spanning the period c. 800 to 1250. Islamic scientific achievements encompassed a wide range of subject areas, especially astronomy, mathematics, and medicine. Other subjects of scientific inquiry included alchemy and chemistry, botany, geography and cartography, ophthalmology, pharmacology, physics, and zoology.

Medieval Islamic science had practical purposes as well as the goal of understanding. For example, astronomy was useful for determining the Qibla, the direction in which to pray, botany had practical application in agriculture, as in the works of Ibn Bassal and Ibn al-'Awwam, and geography enabled Abu Zayd al-Balkhi to make accurate maps. Islamic mathematicians such as Al-Khwarizmi, Avicenna and Jamshīd al-Kāshī made advances in algebra, trigonometry, geometry and Arabic numerals. Islamic doctors described diseases like smallpox and measles, and challenged classical Greek medical theory. Al-Biruni, Avicenna and others described the preparation of hundreds of drugs made from medicinal plants and chemical compounds. Islamic physicists such as Ibn Al-Haytham, Al-Bīrūnī and others studied optics and mechanics as well as astronomy, criticised Aristotle's view of motion.

The significance of medieval Islamic science has been debated by historians. The traditionalist view holds that it lacked innovation, and was mainly important for handing on ancient knowledge to medieval Europe. The revisionist view holds that it constituted a scientific revolution. Whatever the case, science flourished across a wide area around the Mediterranean and further afield, for several centuries, in a wide range of institutions.

Unique Ingredient Identifier

The Unique Ingredient Identifier (UNII) is a non-proprietary, free, unique, unambiguous, non-semantic, alphanumeric identifier linked to a substance's molecular structure or descriptive information by the Substance Registration System (SRS) of the Food and Drug Administration (FDA) and the United States Pharmacopeia (USP).

The SRS is used to generate permanent, unique identifiers for substances in regulated products, such as ingredients in drug and biologic products. The SRS uses molecular structure and descriptive information to define a substance and generate the UNII. The primary means for defining a substance is by its molecular structure as represented on a two-dimensional plane. When a molecular structure is not available (e.g., botanicals), the UNII is defined by descriptive information.The procedures and management of the SRS is provided by the SRS Board which includes experts from both FDA and the United States Pharmacopoeia (USP).

Overview of Pharmacology
Pharmacology: major drug groups
Gastrointestinal tract/
metabolism (A)
Blood and blood
forming organs (B)
Skin (D)
Infections and
infestations (J, P, QI)
Malignant disease
Immune disease
Muscles, bones,
and joints (M)
Brain and
nervous system (N)
Sensory organs (S)
Other ATC (V)
Branches of chemistry
See also
Branches of life science and biology

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