Naranjo Adverse Drug Reaction Probability Scale
Naranjo Adverse Drug Reaction Probability Scale: ten weighted yes/no/unknown questions summing −4 to +13, banded doubtful / possible / probable / definite.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Previous conclusive reports
- Yes
- Event after the drug was given
- Yes
- Improved on dechallenge/antagonist
- Yes
- Reappeared on rechallenge
- unknown
- Alternative causes present
- No
- Reappeared with placebo
- unknown
- Drug in toxic blood concentration
- unknown
- Dose-response relationship
- unknown
- Prior similar reaction
- unknown
- Confirmed by objective evidence
- unknown
Result: Naranjo 6 — probable adverse drug reaction.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Bands
- ≤ 0 doubtful, 1–4 possible, 5–8 probable, ≥ 9 definite.
What you enter
- Previous conclusive reports
- Event after the drug was given
- Improved on dechallenge/antagonist
- Reappeared on rechallenge
- Alternative causes present
- Reappeared with placebo
- Drug in toxic blood concentration
- Dose-response relationship
- Prior similar reaction
- Confirmed by objective evidence
How this is calculated
- Weights
- ten yes/no/don’t-know questions; the event appearing after the drug is +2 but a No is −1, a No on rechallenge is −1, an alternative cause present is −1, placebo reaction +1/−1. Total −4 to +13.
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. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.