Background:Recent studies have raised concerns about hazardous effect of proton pump inhibitors (PPI) in clopidogrel users with acute coronary syndrome (ACS) after percutaneous coronary intervention (PCI). However, limited data are available regarding the impact of the duration of PPI when concurrently used with clopidogrel after PCI. Methods: A total of 2396 patients diagnosed stable angina or ACS underwent PCI were included from March 2003 through June 2008. 219 patients had taken PPI with clopidogrel after PCI. Among them, 156 patients had taken PPI with clopidogrel for initial 6 months after discharge. The 1-year incidences of major adverse cardiac events (MACE), including death, myocardial infarction (MI), target vessel revascularization (TVR) and stent thrombosis (ST) were evaluated Results:Patients treated with PPI and clopidogrel had higher myocardial infarction (non-PPI group vs. PPI group, 1% vs. 3.2%). There was no significant difference in death, TVR, ST and MACE between non-PPI group and PPI group. However the patients treated with clopidogrel and PPI as long as 6 months had higher MI (non-PPI group vs. 6 months PPI group, 1% vs. 3.8%), MACE (non-PPI group vs. 6 months PPI group, 7.9% vs 14.7%). Furthermore, 6 months of PPI treatment with clopidogrel had an independent predictive power in multivariate analysis (Hazard ratio 2.07, 95% CI 1.29-3.33, p=0.002). There was no significant difference between patients treated with clopidogrel and PPI less than 6 months and those with no PPI. Conclusions:In patients underwent PCI following stable angina or ACS, concomitant use of PPI with clopidogrel for more than 6 months is independent risk factor of adverse clinical outcome.