Assessing likelihood of an adverse drug reaction
How to judge whether a drug caused an adverse event, using the Naranjo scale (10 questions, score bands) with a worked example, the WHO-UMC categories, drug-specific tools (RUCAM, ALDEN), their limitations, and when to report to the TGA.
Tier 2Topic overview
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Causality assessment asks how likely it is that this drug caused this event in this patient. It is separate from severity (how bad) and preventability.
- The core clinical evidence is the same in every tool: timing, dechallenge (improvement on stopping), rechallenge (recurrence on re-exposure), alternative causes, previous reports, dose response and objective confirmation such as a drug level.
- The Naranjo scale (1981) is the tool most often examined. The WHO-UMC system is the standard in pharmacovigilance. Event-specific tools exist for liver injury (RUCAM) and SJS/TEN (ALDEN).
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Sources
- Naranjo CA et al. A method for estimating the probability of adverse drug reactions. Clin Pharmacol Ther 1981;30:239-45Clinical Pharmacology and Therapeutics, 1981
- The use of the WHO-UMC system for standardised case causality assessmentUppsala Monitoring Centre
- Reporting adverse eventsAU/NZTherapeutic Goods Administration
- Gallagher RM et al. Development and inter-rater reliability of the Liverpool adverse drug reaction causality assessment tool. PLoS One 2011;6:e28096PLoS One, 2011
- Danan G, Teschke R. RUCAM in drug and herb induced liver injury: the update. Int J Mol Sci 2016;17:14International Journal of Molecular Sciences, 2016
- Sassolas B et al. ALDEN, an algorithm for assessment of drug causality in Stevens-Johnson syndrome and toxic epidermal necrolysis. Clin Pharmacol Ther 2010;88:60-8Clinical Pharmacology and Therapeutics, 2010
- Aronson JK, Ferner RE. Joining the DoTS: new approach to classifying adverse drug reactions. BMJ 2003;327:1222-5BMJ, 2003
- Last updated
- 14 November 2026
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