The Naranjo algorithm is a questionnaire designed by Naranjo et al[1] for determining the likelihood of whether an ADR (drug-related side effects and adverse reactions) is actually due to the medication rather than the result of other factors. Probability is assigned via a score termed definite, probable, possible or doubtful.
An alternative, simpler scale has been proposed by the World Health Organization (WHO).[2][3]
1. Are there previous conclusive reports on this reaction?
Yes (+1) No (0) Do not know or not done (0)
2. Did the adverse event 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)
Scoring