Abstract: Objective To ravel out the concept,connotation and significance of ‘serious’ and ‘severe’ adverse drug reactions (ADRs) /adverse events (AEs), clear out the differences and correlation between the two concepts, and lay a foundation for accurate use in the actual work. Methods Literature research and comparative analysis were introduced to compare and summarize the differences and relationship between the concepts and connotation. Results ‘Serious’ ADR/AE is based on outcome, it is a guidance in determining responsibility in drug safety monitoring, ‘severe’ adverse drug reaction/event is a class of ADR/ADE marked as ‘severe’. Conclusion ‘Serious’ and ‘severe’ ADRs/AEs are not the same and often confused in use, the former is more likely a concept of administration, and the latter is more likely a technical concept. The existence of the two plays a different role, it should be paid attention when use.

Key words: adverse drug reaction, adverse event, classification