# Naranjo algorithm

The Naranjo algorithm, Naranjo Scale, or Naranjo Nomogram is a questionnaire designed by Naranjo et al. for determining the likelihood of whether an ADR (adverse drug reaction) is actually due to the drug rather than the result of other factors. Probability is assigned via a score termed definite, probable, possible or doubtful. Values obtained from this algorithm are sometimes used in peer reviews to verify the validity of author's conclusions regarding adverse drug reactions. It is also called the Naranjo Scale or Naranjo Score.

## Questionnaire

1. Are there previous conclusive reports on this reaction?

Yes (+1) No (0) Do not know or not done (0)

2. Did the adverse events appear after the suspected drug was given?

Yes (+2) No (-1) Do not know or not done (0)

3. Did the adverse reaction improve when the drug was discontinued or a specific antagonist was given?

Yes (+1) No (0) Do not know or not done (0)

4. Did the adverse reaction appear when the drug was readministered?

Yes (+2) No (-1) Do not know or not done (0)

5. Are there alternative causes that could have caused the reaction?

Yes (-1) No (+2) Do not know or not done (0)

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

Yes (-1) No (+1) Do not know or not done (0)

7. Was the drug detected in any body fluid in toxic concentrations?

Yes (+1) No (0) Do not know or not done (0)

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

Yes (+1) No (0) Do not know or not done (0)

9. Did the patient have a similar reaction to the same or similar drugs in any previous exposure?

Yes (+1) No (0) Do not know or not done (0)

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

Yes (+1) No (0) Do not know or not done (0)

Scoring

• ≥ 9 = definite ADR
• 5-8 = probable ADR
• 1-4 = possible ADR
• 0 = doubtful ADR

## References

• Naranjo CA, Busto U, Sellers EM, et al. (1981). "A method for estimating the probability of adverse drug reactions". Clin. Pharmacol. Ther. 30 (2): 239–45. doi:10.1038/clpt.1981.154. PMID 7249508.