Table 5.

Adverse drug reaction (ADR)

Unrelated	An adverse event (AE) that is not related to drug use
Unlikely	An AE for which an alternative explanation is more likely (e.g., concomitant drugs and diseases), or the relationship in time suggests that a causal relationship is unlikely
Possible	An AE that might be caused by drug use. An alternative explanation (e.g., concomitant drugs and diseases) is inconclusive. The relationship in time is reasonable; therefore, the causal relationship cannot be excluded
Probable or likely	An AE that might be due to drug use. The relationship in time is suggestive (e.g., confirmed by a dechallenge). An alternative explanation is less likely (e.g., concomitant drugs or diseases)
Certain	An AE that is listed as a possible ADR and cannot be reasonably explained by an alternative explanation (e.g., concomitant drugs and diseases). The relationship in time is highly suggestive; it is confirmed by a dechallenge and rechallenge