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This glossary gives definitions for the main regulatory terms used on this website and in European Medicines Agency (EMA) documents.

Click on a letter below to see terms beginning with that letter.

Disclaimer: EMA has developed the definitions in this glossary to help this website's users understand regulatory terminology. Definitions may differ from those given in European Union legislation.


accelerated assessment

Rapid assessment of medicines in the centralised procedure that are of major interest for public health, especially ones that are therapeutic innovations. Accelerated assessment usually takes 150 evaluation days, rather than 210.

For more information, see: accelerated assessment.

access to documents

Activities relating to public access to European Medicines Agency documents.

For more information, see access to documents.

active substance

The substance responsible for the activity of a medicine.

active substance master file

Documentation providing detailed information on the manufacturing of the active substance of a medicine.

For more information, see Electronic Active Substance Master Files (eASMF).


An ingredient in a medicine that increases or modifies the activity of the other ingredients. Adjuvants are often included in vaccines to enhance the body’s immune response.

advanced therapy medicinal product

A medicine for human use that is based on genes, cells or tissue engineering.

For more information, see advanced therapies.

adverse drug reaction

A noxious and unintended response to a medicine.

adverse event

An untoward medical occurrence after exposure to a medicine, which is not necessarily caused by that medicine.

ancillary human blood derivative

A medicine derived from human blood or plasma that is incorporated within a medical device, where the main mode of action is due to the device.

ancillary medicinal substance

A medicine that is incorporated within a medical device where the main mode of action is due to the device.

For more information, see ancillary medicinal substances.

annual re-assessment

An annual review of the benefits and risks of a medicine that has been authorised under exceptional circumstances. As part of the process, the specific obligations imposed on the marketing-authorisation holder are also reviewed.

For more information, see questions and answers: annual re-assessment.

Article-58 application

An application for a scientific opinion on the use of a human medicine intended exclusively for markets outside of the European Union. Medicines eligible for this procedure are used to prevent or treat diseases of major public health interest.

For more information, see Article-58 applications: regulatory and procedural guidance.

ATC code

The Anatomical Therapeutic Chemical code: a unique code assigned to a medicine according to the organ or system it works on and how it works. The classification system is maintained by the World Health Organization (WHO).

For more information, see WHO Collaborating Centre for Drug Statistics Methodology.