Medicine Adverse Effect: Undesired harmful effect resulting from a medication or other medical intervention

An adverse effect may be called a "side-effect" (when it is less important than the therapeutic effect).

It may result from an unsuitable or incorrect dosage or procedure (which could be caused by medical error). Some adverse effects happen only at the beginning or a change of a treatment. Medical error was the third most common cause of death in the United States in 2019.

In many countries, adverse effects have to be reported and researched in clinical trials and included into the patient information accompanying medical devices and drugs for sale to the public. This is called pharmacovigilance.

• Toxicology

• Patient Safety Network. An extremely useful site, with a glossary and articles on all kinds of threats to patient safety, including adverse effects, drug reactions, medical error, iatrogenesis, etc.
• Australian Adverse Drug Reactions Bulletin Archived 2005-07-28 at the Wayback Machine - published bimonthly by ADRAC
• Drugs of Concern Archived 2005-12-14 at the Wayback Machine DrugIntel.com site for tort lawyers with up-to-date information on drugs that cause severe adverse effects)
• Medication Errors a FDA site.
• Medical Product Safety Information. MedWatch, a useful page from Food and Drug Administration, listing safety alerts for drugs, biologics, devices and dietary supplements, recalls, market withdrawals, public health advisories, links to the VAERS and MAUDE databases, etc.)
• Medical Devices Safety National Library of Medicine (Medline Plus, useful lists of conventional drug and medical device articles and websites)
• When Medicine Hurts Instead of Helps Archived 2008-07-05 at the Wayback Machine - A special report by the Alliance for Aging Research on ADRs.