Emergency Medicine General Medicine Pharmacology Moderate — widely used standardised causality assessment tool

Naranjo Adverse Drug Reaction Scale

Standardised questionnaire to assess the probability that an adverse drug reaction (ADR) is caused by a specific drug

1. Previous conclusive reports of this reaction?*

2. Did the adverse event appear after the drug was given?*

3. Did the reaction improve when the drug was stopped or an antagonist given?*

4. Did the reaction reappear when the drug was re-administered?*

5. Alternative causes that could solely have caused the reaction?*

6. Did the reaction reappear when a placebo was given?*

7. Was the drug detected in the blood (or other fluids) in toxic concentrations?*

8. Was the reaction more severe when the dose was increased, or less severe when decreased?*

9. Did the patient have a similar reaction to the same or similar drug before?*

10. Was the adverse event confirmed by objective evidence?*

Score interpretation

Doubtful ADR -4–0

Score ≤ 0: Unlikely to be a drug reaction.

→ Explore alternative diagnoses. Cautious re-challenge may be considered.

Possible ADR 1–4

Score 1–4: Possible adverse drug reaction.

→ Document reaction. Review drug appropriateness. Monitor closely.

Probable ADR 5–8

Score 5–8: Probable adverse drug reaction.

→ Discontinue or change offending drug. Report to Yellow Card (UK MHRA).

Definite ADR 9–13

Score ≥ 9: Definite adverse drug reaction.

→ Discontinue drug immediately. Report Yellow Card. Document allergy/ADR clearly in notes.

Interpretation bands for the Naranjo ADR. Apply clinical judgement and local guidance.

References

Naranjo CA, et al. A method for estimating the probability of adverse drug reactions. Clin Pharmacol Ther. 1981;30(2):239–245.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Pathways

📚 MRCEM Revision

Featured in these MRCEM clinical pathways

The Naranjo ADR is covered in detail — with RCEM/NICE evidence base, indications and pitfalls — in the following exam-focused pathways on our sister siteReviseMRCEM.

Toxidromes

MRCEM Primary / Intermediate / OSCE candidates: each pathway includes exam-style questions, RCEM/NICE citations, and FAQ summaries.

Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.

Score interpretation

References

Related