What are Drug Interaction Severity Ratings?

Both professional and consumer drug interaction reports use the same 4-level drug interaction severity rating system detailed below.

Level 1 (Contraindicated)

The use of these medications together is contraindicated. Rare exceptions may exist. Drug interactions identified as contraindicated in the FDA-approved prescribing information are included, regardless of other clinical data.

Level 2 (Major)

The use of these medications together is expected to result in a major drug interaction; action should be taken before the drugs are coadministered or at the time of initiation. Dosage adjustments, increased monitoring, and/or consideration of alternative therapy are recommended. The use of these medications together may be contraindicated in a select group of patients.

Level 3 (Moderate)

The use of these medications together may result in unintended clinical effects. While preemptive action is not usually required, the patient should be monitored and counseled about possible manifestations of the interaction and when to seek medical attention; therapy adjustments may be necessary if a clinically relevant interaction occurs. Recommendations to separate administration times to avoid an interaction are included.

Level 4 (Minor)

Data suggest that the use of these medications together does not usually result in a clinically significant interaction in most patients; however, the possibility of an interaction cannot be dismissed.