Glossary of pharmacovigilance terms

Definitions are important in any scientific field to ensure that everyone is talking about exactly the same thing. On this page, we offer definitions of the major concepts and terms used in pharmacovigilance, many of which you will find in context on this website. Definitions evolve over time and this list reflects changes that have been happening and are in progress. Many terms are used variously across the world, and some are used loosely or even inaccurately; old terms linger on when new thinking has superseded them. We hope you will find this is a useful and sensible guide for the time being; we will value your contributions to refine and update the content.

Absolute risk: The probability of an event affecting members of a particular population (e.g.1 in 1,000).

Adherence: A patient’s careful and willing observance of the guidelines for taking a medicine or managing a therapy. This term has largely replaced the term compliance.

Adverse drug reaction (ADR): A harmful effect suspected to be caused by a drug. This term has been used quite loosely to include all kinds of adverse events, many of which are not ‘reactions’ in the strict sense at all, and have not been subject to any assessment of causality. The term is properly reserved for late-stage analysis when the association between a medicine and an adverse effect has moved beyond 'unmeasurable' or 'uncertain'.

Adverse effect: A negative or harmful patient outcome that seems to be associated with treatment, including there being no effect at all.

Adverse event: Any negative or harmful occurrence that takes place during treatment, that may or may not be associated with a medicine. Note. A fall could be such an event that may – or may not – have any association with a medicine.

Association: Events associated in time but not necessarily linked as cause and effect (temporal association).

Attributable risk: Difference between the risk in an exposed population (absolute risk) and the risk in an unexposed population (reference risk); the difference from the absolute risk in the probability of an event happening, attributable to a drug or other variable

Benefit: (a) positive therapeutic effects of treatment in an individual; (b) positive health, social or psychological effects of treatment from the patient’s perspective. 

Benefit-harm: A description or assessment of both positive and negative effects of a medicine (not necessarily expressed in quantitative terms) as far as they are known, and as perceived by an individual. This is the critical information that health professionals and patients need to make wise therapeutic decisions. The perspectives of professionals and patients on the issues may differ.

Benefit-risk: ‘Benefit-risk’ is a logically mismatched pair, the more accurate, benefit-harm, is preferable. See also effectiveness-risk.

Causal relationship: Where there is a demonstrable cause-effect association between two events. Standardised case causality assessment (pdf)

Common: In pharmacovigilance, an event with a probability between 1 in 100 and 1 in 10, or 1%-10%.

Compliance: Faithful obedience by the patient to the prescriber’s instructions. This term has lost favour because of its implication of a passive, compliant patient, as opposed to a willing partner in the process. See adherence, the currently preferred alternative.

Conditional market authorisation: Approval with constraints, e.g. time limitation, of a medicine on the basis of less comprehensive data than normally required, allowing for more rapid access to novel medicines.

Consumer: The use of the term consumer can be misleading. A person may or may not be an actual consumer of health care or medicines at a given time, but all members of the general public are potential patients/consumers. For the latter group the term general public is preferred. The term patient is normally used when referring to actual consumers of medical or health care.

Control group: The comparison group in medicine-trials not being given the studied medicine.

Drug: See medicinal product/medicine: commonly used as a synonym for these terms, drug is falling out of favour in professional medical circles because of the prevalence of its use to describe illicit substances.

Effectiveness: A measure of the chances or odds (probability) of a medicine working positively as expected for patients.

Effectiveness-risk: A comparison of the statistical chances (probability) of a medicine working as expected and/or causing harm. This is the correct term for this comparison, not ‘benefit-risk’, which is a logically mismatched pair.

Efficacy: A measure of the extent to which a chemical substance or medicine works positively under laboratory conditions and in a selected group of patients.

Epidemiology: The study of disease in populations.

Event: A specific, identifiable happening or occurrence, e.g. the taking of a medicine; the experience of an adverse effect.

Excipients: Materials included to make a pharmaceutical formulation (e.g. a tablet) apart from the active drug substance, e.g. fillers, stabilisers, flavouring agents, colouring agents.

General public/the public: People collectively as members of the community.

Generics: Medicinal products containing the same, or near-identical, active ingredients as the originally approved branded (innovator) product. Dosage form, safety, strength, route of administration, quality, performance characteristics and intended use should be equivalent; but excipients may differ.

Harm: The damage or injury that is or might be caused by a medicine, including death. The concept extends to social and psychological damage or impairment, especially from the patient’s perspective.

Hazard: The intrinsic chemical or biological characteristics of a medicine or its use that have the potential to cause harm. 

Health professional/healthcare professional: Person who is trained and licensed to provide health care to humans. Includes: doctor, nurse, dentist, pharmacist, midwife; excludes: veterinarian.

Herbal medicine: The use of plants for medicinal purposes; also known as botanical medicine or phytomedicine. See also Traditional medicine.

Homeopathy: A treatment system based on the belief that disease symptoms can be cured by small doses of substances which produce similar symptoms in healthy people. 

Incidence: Number of new cases of an outcome which develop over a defined time period in a defined population at risk. Note. Incidence is a frequency measurement of outcome development over time (compare prevalence).

Indication: Symptoms or disease for which a remedy or treatment is advisable or necessary. The concept ‘reason for use’ is broader and may include off-label use, misuse etc. In pharmacovigilance, the actual reason for use should ideally be recorded.

Individual case safety report (ICSR): Reports sent by health professionals or patients when an adverse effect has occurred in a patient taking one or more medicines. These have also been referred to as adverse drug reaction (ADR) reports or adverse event (AE) reports. See also Pharmacovigilance reporting systems.

Media: Means of communication. Note. This term includes any channel of communication, and may also refer to those engaged in them.

Mass media: Main channels of communication to the general public. Includes: newspapers, radio, television and internet. Includes journalists, editors, bloggers etc., engaged in such communication. See also Social media.

Medicinal product/medicine: Product intended to be administered to humans for treating or preventing disease; with the view to making a medical diagnosis; or to restore, correct or modify physiological functions.

Member countries: Countries that have joined the WHO Programme for International Drug Monitoring, fulfilling the membership criteria.

National centres: Organisations or entities recognised by government to represent their country in relation to pharmacovigilance in the WHO Programme for International Drug Monitoring.

Odds: Probability of an occurrence p divided by the probability of its non-occurrence (1-p).

Odds ratio: Ratio of the odds in a given population and the odds in another population. Note. In case-control studies the odds ratio is the odds of exposure (to a medicinal product) in cases (e.g. individuals with an adverse effect) divided by the odds of exposure in controls (e.g. individuals without the adverse effect). The odds ratio provides an estimate of the relative risk.

Over the counter (OTC): A medicine available for sale without a prescription

Patient: Person awaiting or under medical or health care treatment. This concept includes anyone taking medicines, also those who are self-medicating.

Pharmacoepidemiology: Branch of epidemiology (see above) dealing with the effects of medicines in populations.

Pharmacology: Study of the uses, effects and modes of action of drugs.

Pharmacovigilance: The science and activities relating to the detection, assessment, understanding and prevention of adverse effects or any other possible drug-related problems. [WHO 2002]

Pharmacovigilance reporting systems: The core data-generating system of pharmacovigilance, relying on healthcare professionals and patients to identify and report any suspected adverse effects from medicines to their local or national pharmacovigilance centre or to the manufacturer. Also referred to as postmarketing/safety surveillance/spontaneous reporting systems.

Phocomelia: Characteristic deformity caused by exposure to thalidomide in the womb, also very rarely occurring spontaneously. Means: limbs like a seal.

Phytotherapy: Western-style, scientific treatment with plant extracts or materials.

Placebo: An inactive substance (often called a sugar pill) given to a group being studied to compare results with the effects of an active substance.

Pre-marketing: The developmental stage before a drug is approved and available for prescription or sale to the public.

Post-marketing: The stage when a drug is approved and generally available on the market. See also Conditional market authorisation.  

Prescriber: Health professional licensed by law to prescribe. Note. A prescriber may have a limited licence, for instance allowing prescription of certain categories of medicinal products, e.g. in some countries midwives are licensed to prescribe only oral contraceptives.

Prescription only medicine (POM): A drug licensed for use only by prescription.

Prevalence: Number of existing cases of an outcome in a defined population at a given point in time. Note. Prevalence is calculated as a proportion (cases divided by total in population), often expressed as a percentage.

Prophylaxis: Prevention or protection.

Proportion: Number of cases of an outcome divided by the total number of individuals in the studied population. Note. A percentage is the proportion (cases divided by total in population) multiplied by 100.

Rare: In pharmacovigilance, an event with a probability between 1 in 10,000 and 1 in 1,000, or 0.01% and 0.1%.

Rate: Number of cases of an outcome divided by the total person-time of observation. Note. A rate figure normally has a large whole number as a multiplier, reflecting the actual, or a scaled-up, population (e.g. 1,000, 10,000, 20,000).

Rational drug use: A visionary concept implying the achievement of optimal prescribing and use of drugs.

Reference risk: Risk in a population of unexposed persons. Synonyms: Baseline risk, background risk. Note. The unexposed population refers to a reference group, as closely comparable to the exposed population as possible, apart from the exposure.

Regulatory authority: The legal authority in any country with the responsibility for regulating all matters relating to drugs.

Relative risk: Ratio (comparison) of the risk in an exposed population (absolute risk) and the risk in an unexposed population (reference risk). Note. Relative risk is the result of a relative comparison between outcome frequency measurements, e.g. incidences.

Risk: The probability of harm being caused; the probability (chance, odds) of an occurrence. Note 1. The term risk normally, but not always, refers to a negative outcome. Note 2. Contrary to harm, the concept of risk does not involve any reference to the nature or severity of an outcome.

Serious: An adverse event or reaction that results in death; requires hospitalisation or extension of hospital stay; results in persistent or significant disability or incapacity; is life-threatening. Note. This contrasts with severe, which is used to indicate intensity (as in severe headache).

Side effect: Any unintended outcome that seems to be associated with treatment, including negative or positive effects. This term has come to be used exclusively in the sense of adverse effect; this loses the important dimension of potential reference to unintended positive effects as well as linguistically masking the adverse element of a negative side effect.

Signal: There are several definitions of signal, such as that by CIOMS and that by WHO (see What is a signal?). In essence, a signal is a hypothesis of a risk with a medicine, with various levels of evidence and arguments to support it. The complexity of the signal detection process cannot easily be captured in a single, precise definition. In addition to detecting previously unknown risks with medicines, signal detection should aim to find and communicate any important and relevant information that adds to previous safety knowledge about a medicine, including also risk factors/at risk groups, details of severity, time at risk, and duration of adverse effects.

SSFFCs: There is currently no universally agreed definition of what used to be widely known as Counterfeit medicine. Since the 70th World Health Assembly in 2017, WHO is using the term Substandard and Falsified (SF) medical products. For more information see the WHO website

Stakeholder: Individual, or group of individuals, with a legitimate interest and responsibility in a human endeavour, e.g. pharmacovigilance. Their interest may be because they will have a role in implementing decisions, or because they will be affected by actions taken.

Thalidomide: Drug prescribed in the 1950s and early 1960s as a mild sleeping pill and remedy for morning sickness in pregnant women. Led to serious birth defects (see Phocomelia). The disaster was the catalyst for the formation of the WHO Programme for International Drug Monitoring. Thalidomide has returned as a treatment of certain cancers and a complication of leprosy.

Traditional medicine: The sum total of the knowledge, skills, and practices based on the theories, beliefs, and experiences indigenous to different cultures, whether explicable or not, used in the maintenance of health as well as in the prevention, diagnosis, improvement or treatment of physical and mental illness. [WHO]

Last modified on: November 10, 2020