Naranjo ADR Probability Scale

Scores ten standardized yes/no/unknown questions on an observed adverse event to estimate the probability that a drug actually caused it, banding causality from doubtful to definite.

1. Are there previous conclusive reports on this reaction?

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

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

4. Did the adverse event reappear when the drug was readministered? (answer "No" only if rechallenge was actually done and the event did not recur; otherwise "Do not know")

5. Are there alternative causes (other than the drug) that could on their own have caused the reaction?

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

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

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

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

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