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Practice Clinical updates

Adverse drug reactions

BMJ 2018; 363 doi: (Published 06 November 2018) Cite this as: BMJ 2018;363:k4051

Linked opinion

Helping patients understand adverse drug reactions

This article has a correction. Please see:

  1. Robin E Ferner, honorary professor of clinical pharmacology1,
  2. Patricia McGettigan, reader in clinical pharmacology and medical education2
  1. 1West Midlands Centre for Adverse Drug Reactions, City Hospital, Birmingham B18 7QH, UK
  2. 2William Harvey Research Institute, Queen Mary University of London, London EC1M 6BQ, UK
  1. Correspondence to: R E Ferner r.e.ferner{at}

What you need to know

  • Prescribers need to balance the possibility of causing harm against the probability of benefit

  • Some drugs cause characteristic adverse reactions, whereas others cause non-specific or bizarre effects

  • Some adverse drug reactions occur within minutes of administration, whereas others can present years after treatment

  • The dose of the drug, time since starting treatment, and potential susceptibility of the patient can help determine if adverse drug reactions enter the differential diagnosis

  • Report suspected serious or unusual adverse drug reactions to the national medicines regulator; you don’t have to be certain in order to report

No medicine is entirely safe, so the therapeutic benefit needs to be balanced against the risk of an adverse drug reaction. The pharmacovigilance environment has changed in the past two decades, with biological therapies, complex multidrug regimens, genetic testing, “big data,” and new regulation for drug safety.1 In this clinical update we describe some principles that guide prevention, recognition, and response to adverse drug reactions.

Sources and selection criteria

We searched Medline for “exp drug-related side effects and adverse reactions/”, which gave 103 893 hits. We limited the search to 2008 onwards; to “exp drug-related side effects and adverse reactions/classification, diagnosis, diagnostic imaging, etiology, genetics, prevention, and control”; and to core medical journals, which gave 1236 titles to look through. We also used the UK Medicines and Healthcare products Regulatory Agency’s Drug Safety Update, the US Food and Drug Administration’s MedWatch alerts, the journal Reactions Weekly, Meyler’s Side Effects of Drugs Annual, and our own reference collections to identify relevant articles.

What is an adverse drug reaction?

Medicines have unintended side effects, and if any of these is harmful, the patient has an adverse drug reaction.2 The European Medicines Agency (EMA) defines an adverse drug reaction as “a response to a medicinal product which is noxious and unintended.”3 This definition now extends beyond …

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