Abstract: OBJECTIVE To improve the ADEs reporting by developing medication event trigger tools to detect ADEs.METHODS The present study was a multi-center, retrospective study in 3 tertiary teaching hospitals in Zhejiang province in 2015. Patients were monitored using electronic trigger tools designed to detect patients with over-anticoagulationUsing laboratory test results of International Normalized Ratio (INR) values ≥ 6 if warfarin was concurrently prescribed or potential opioid overdose (administration of naloxone as a signal of over-sedation caused by opioid analgesics). Case note review removed the duplicates and the false positive ADEs. And medical incident reports were also reviewed. RESULTS The INR ≥ 6 electronic trigger identified 39 potential ADEs and the naloxone electronic trigger identified 11 potential ADEs. The available case note review identified 9 ADEs for the INR ≥ 6 triggerpositive predictive value (PPV) was 23.1% and 4 ADEs (PPV 36.4%) for the naloxone trigger. No serious ADEs over-coagulation with warfarin and over-sedation with opioid medication were newly discovered using the trigger tools. Nearly all of the ADEs (12/13) discovered by the trigger tools had not been voluntarily reported to the hospital's event reporting program. CONCLUSION It's showed that the trigger tools is useful to discover ADEs that has not been voluntarily reported or evaluated. Incorporating electronic trigger tools with prescription and laboratory test data can improve the detection of ADEs, and potentially lead to methods to avoid underreporting them.