Naranjo Adverse Drug Reaction Probability Scale

Estimates the probability that a clinical event was caused by a drug from 10 questions (definite / probable / possible / doubtful).

Evidence tier: Validated instrument.

Formula / logic

Sum of 10 weighted yes/no/unknown items (range −4 to +13). Causality: ≥9 definite; 5-8 probable; 1-4 possible; ≤0 doubtful.

Interpretation

A general ADR-causality instrument applicable to drug allergy and any suspected drug-induced event. "Do not know" scores 0 for every item.

Evidence & citations

  1. Naranjo CA, Busto U, Sellers EM, et al. A method for estimating the probability of adverse drug reactions. Clin Pharmacol Ther. 1981;30(2):239-245. PMID 7249508

Clinician decision support. Verify against the cited source. Not a substitute for clinical judgment. 100% on-device; no patient data is stored or transmitted.