An adverse event (AE), which is also known as an adverse effect, is an undesirable, though not necessarily unexpected, medical occurrence in a patient in reaction to a substance that is administered. The substance could be any type of pharmaceutical drug, vaccine, or therapy. An adverse event may not be the result of the treatment itself, however if a reaction occurs in the patient following the treatment, the case must be investigated. Such reactions can range in severity from mild to fatal.
It is critical that adverse events are reported when they occur. Adverse events are typically graded as:
- Grade 1: Mild AE
- Grade 2: Moderate AE
- Grade 3: Severe AE
- Grade 4: Life-threatening or disabling AE
- Grade 5: Death related to AE
Adverse events are also classified into five categories:
- Negative and accidental reaction: This can include irregular lab results, symptoms, or disease correlated with the treatment.
- A reaction that “causally” corresponds to medication used during clinical trials.
- Serious: An AE that leads to disability, hospitalization, or death.
- Suspected: Any adverse event for which there is a reasonable possibility that the drug caused the adverse event.
- Suspected unexpected: An adverse event that is thought to be caused by a drug, but not necessarily consistent with the drug.