Any undesired medical effect in a patient or clinical investigation subject following the administration of a pharmaceutical product which does not necessarily have to have a causal relationship with the administered treatment.

An adverse event (AE) can be any unfavourable and unintended event, abnormal laboratory finding, symptom or disease temporally associated with the use of a medicinal product, regardless of whether the event is considered related to the medicinal product or not.

In the pre-approval clinical period of a new medicinal product or new application for an existing medicinal product, particularly as the therapeutic dose may not yet be established, all unintended responses related to any dose are considered adverse drug events.

A ‘severe’ adverse event may be of relatively minor clinical significance, e.g. severe headache. This term describes the intensity. Conversely, a ‘serious’ adverse event is based on outcome or action criteria, usually associated with events threatening a patient’s life or functioning. Seriousness (not severity) serves as a guide for defining regulatory reporting obligations.

Expedited reporting of adverse drug events is a regulatory obligation and is intended to make regulators, investigators, and other appropriate parties aware of new, important information on serious reactions to a drug and on a drug itself. These adverse events tend to be described as ‘unexpected’ or ‘expected’, depending on if the phenomena have been previously observed.