This code system http://terminology.hl7.org/CodeSystem/adverse-event-causality-assess defines the following codes:
| Code | Display | Definition |
| certain | Certain | i) Event or laboratory test abnormality, with plausible time relationship to drug intake; ii) Cannot be explained by disease or other drugs; iii) Response to withdrawal plausible (pharmacologically, pathologically); iv) Event definitive pharmacologically or phenomenologically (i.e. an objective and specific medical disorder or a recognized pharmacological phenomenon); or v) Re-challenge satisfactory, if necessary. |
| probably-likely | Probably/Likely | i) Event or laboratory test abnormality, with reasonable time relationship to drug intake; ii) Unlikely to be attributed to disease or other drugs; iii) Response to withdrawal clinically reasonable; or iv) Re-challenge not required. |
| possible | Possible | i) Event or laboratory test abnormality, with reasonable time relationship to drug intake; ii) Could also be explained by disease or other drugs; or iii) Information on drug withdrawal may be lacking or unclear. |
| unlikely | Unlikely | i) Event or laboratory test abnormality, with a time to drug intake that makes a relationship improbable (but not impossible); or ii) Disease or other drugs provide plausible explanations. |
| conditional-classified | Conditional/Classified | i) Event or laboratory test abnormality; ii) More data for proper assessment needed; or iii) Additional data under examination. |
| unassessable-unclassifiable | Unassessable/Unclassifiable | i) Report suggesting an adverse reaction; ii) Cannot be judged because information is insufficient or contradictory; or iii) Data cannot be supplemented or verified. |