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[Pharmacology](https://durgical.com/en/pharmacology/) · Topic

# Pharmacovigilance and post-marketing safety

How adverse effects are detected, reported and acted on after a medicine is approved, and how health workers and patients can report them.

Updated 2026-11-01

WHO defines pharmacovigilance as the science and activities concerned with detecting, assessing, understanding and preventing adverse effects and other medicine-related problems. Clinical trials cannot find every risk, so countries collect reports of suspected reactions, look for signals, and update labels or restrict use when needed. WHO hosts the Programme for International Drug Monitoring, which links national centres.

## Key points

- Spontaneous reporting of suspected adverse reactions is the core of pharmacovigilance; a report does not have to prove causation.
- A signal is a new possible link between a drug and an event, or a new aspect of a known one, that deserves checking.
- Outcomes include label changes (new warnings, boxed warnings), restricted use, risk-management programmes and, rarely, withdrawal.
- Colombia: INVIMA runs the national reporting system and the Red Nacional de Farmacovigilancia; health professionals report through VigiFlow.
- United States: the FDA's MedWatch receives reports from health professionals, patients and consumers.

## Why trials are not enough

Trials enrol a limited number of selected people for a limited time. Rare reactions, reactions after long use, effects in children, older adults, pregnancy or people with many illnesses, and interactions often appear only after many people start using the drug.

## From report to action

- Report: who, which drug, what happened, when, outcome
- Signal detection: national centres and WHO compare reports across countries
- Assessment: causality, frequency, severity, other data (studies, mechanisms)
- Action: label update, safety communication, restrictions, monitoring programmes, withdrawal

## Examples of label changes

Several pharmacogenetic warnings came from post-marketing experience and later studies: the clopidogrel boxed warning on CYP2C19 poor metabolisers, and the HLA-B*15:02 warning for carbamazepine and severe skin reactions. The FDA table of pharmacogenomic biomarkers shows which labels now carry such information.

## What to report and how

Serious, unexpected or new reactions, reactions to new medicines, medication errors, lack of effect and suspected quality problems are worth reporting. In Colombia, health professionals report to INVIMA through VigiFlow and institutions join the Red Nacional de Farmacovigilancia; manufacturers have their own reporting duties.

## Memory aid

Suspect it, report it: one report can be the first dot of a signal.

## Test yourself

Think of the answer, then tap the question to see it.

## How does WHO define pharmacovigilance?

As the science and activities relating to detecting, assessing, understanding and preventing adverse effects and other medicine-related problems.

## Does a clinician need to be sure a drug caused a reaction before reporting it?

No. A suspicion is enough; spontaneous reports are pooled and assessed to detect signals.

## Through which system do health professionals in Colombia report adverse drug reactions to INVIMA?

Through VigiFlow, as part of INVIMA's national pharmacovigilance reporting system.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/topics/pharmacovigilance-and-post-marketing-safety/)

## Related classes

- [Antiplatelet drugs](https://durgical.com/en/pharmacology/classes/antiplatelet-drugs/)
- [Vitamin K antagonists](https://durgical.com/en/pharmacology/classes/vitamin-k-antagonists/)

## Example drugs

- [Clopidogrel](https://durgical.com/en/pharmacology/clopidogrel/)
- [Warfarin](https://durgical.com/en/pharmacology/warfarin/)
- [Carbamazepine](https://durgical.com/en/pharmacology/carbamazepine/)
- [Abacavir](https://durgical.com/en/pharmacology/abacavir/)

[← All of pharmacology](https://durgical.com/en/pharmacology/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Pharmacovigilance](https://www.who.int/teams/regulation-prequalification/regulation-and-safety/pharmacovigilance) (World Health Organization, 2026); [Servicios en Línea Farmacovigilancia - INVIMA](https://www.invima.gov.co/farmacovigilancia) (Instituto Nacional de Vigilancia de Medicamentos y Alimentos (INVIMA), Colombia, 2026); [MedWatch: The FDA Safety Information and Adverse Event Reporting Program](https://www.fda.gov/safety/medwatch-fda-safety-information-and-adverse-event-reporting-program) (U.S. Food and Drug Administration, 2026); [Table of Pharmacogenomic Biomarkers in Drug Labeling](https://www.fda.gov/drugs/science-and-research-drugs/table-pharmacogenomic-biomarkers-drug-labeling) (U.S. Food and Drug Administration, 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/topics/pharmacovigilance-and-post-marketing-safety/