Table 2. Naranjo score for the identification of adverse drug reactions.

Question (score depends on answer)	Patient history is usually sufficient to answer the question
1. Is the adverse event (AE) a known adverse drug reaction (ADR)? (yes: +1; no: 0; unknown: 0)	Yes
2. Did the AE occur following administration of the suspected drug? (yes: +2; no: –1; unknown: 0)	Yes
3. Did the AE improve following discontinuation of the suspected precipitating drug or administration of a specific antagonist? (yes: +1; no: 0; unknown: 0)	No
4. Did the AE reoccur following resumption of the suspected precipitating drug? (yes: +2; no: –1; unknown: 0)	No
5. Are there alternative causes for the AE? (yes: –1; no: +2; unknown: 0)	Yes
6. In the case that a placebo was given: did the AE reoccur? (yes: –1; no: +1; unknown: 0)	No
7. Was there a toxic concentration in body fluids? (yes: +1; no: 0; unknown: 0)	No
8. Did a dose escalation exacerbate, or a dose reduction improve, symptoms? (yes: +1; no: 0; unknown: 0)	No
9. Have similar drugs caused the patient to experience similar AEs in the past? (yes: +1; no: 0; unknown: 0)	Yes
10. Can the AE be objectively confirmed? (yes: +1; no: 0; unknown: 0)	Yes
Probability that the AE is an ADR …	Point score
… Definite	≥ 9
… Probable	5–8
… Possible	1–4
… Doubtful	≤ 0
Maximum achievable score, assuming that…	Point score
… all information is available	13
… only patient history is available	6
… only patient history is available and question 5 was answered with “yes,” question 7 with “unknown,” and question 9 with “no” or “unknown”	3