Table 3: Naranjo’s classification criteria.

Question Yes No Do not know
Are there previous conclusion reports on this reaction? +1 0 0
Did the adverse event appear after the suspect drug was administered? +2 –1 0
Did the adverse reaction improve when the drug was discontinued or a specific antagonist was administered? +1 0 0
Did the adverse reaction reappear when drug was re-administered? +2 –1 0
Are there alternate causes [other than the drug] that could solely have caused the reaction? –1 +2 0
Did the reaction reappear when a placebo was given? –1 +1 0
Was the drug detected in the blood [or other fluids] in a concentration known to be toxic? +1 0 0
Was the reaction more severe when the dose was increased or less severe when the dose was decreased? +1 0 0
Did the patient have a similar reaction to the same or similar drugs in any previous exposure? +1 0 0
Was the adverse event confirmed by objective evidence? +1 0 0

Scoring for Naranjo algorithm: >9 = definite ADR; 5–8 = probable ADR; 1–4 = possible ADR; 0 = doubtful ADR.