Table 2. WHO-UMC causality assessment scale.
WHO-UMC: World Health Organization-Uppsala Monitoring Centre
| Causality term | Causality term |
| Certain | · Event or laboratory test abnormality, with a plausible time relationship to drug intake |
| · Cannot be explained by disease or other drugs | |
| · Response to withdrawal plausible (pharmacologically, pathologically) | |
| · Event definitive pharmacologically or phenomenologically (i.e., an objective and specific medical disorder or a recognised pharmacological phenomenon) | |
| · Rechallenge satisfactory, if necessary | |
| Probable / Likely | · Event or laboratory test abnormality, with reasonable time relationship to drug intake |
| · Unlikely to be attributed to disease or other drugs | |
| · Response to withdrawal clinically reasonable | |
| · Rechallenge not required | |
| Possible | · Event or laboratory test abnormality, with reasonable time relationship to drug intake |
| · Could also be explained by disease or other drugs | |
| · Information on drug withdrawal may be lacking or unclear | |
| Unlikely | · Event or laboratory test abnormality, with a time to drug intake that makes a relationship improbable (but not impossible) |
| · Disease or other drugs provide plausible explanations | |
| Conditional / Unclassified | · Event or laboratory test abnormality |
| · More data for proper assessment needed, or | |
| · Additional data under examination | |
| Un-assessable / Unclassifiable | · Report suggesting an adverse reaction |
| · Cannot be judged because the information is insufficient or contradictory | |
| · Data cannot be supplemented or verified |