Combined antiplatelet treatment with aspirin and clopidogrel is pivotal to minimize periprocedural adverse events in patients who undergo percutaneous coronary intervention. However, there is debate on the best clopidogrel loading dose. The investigators performed a systematic review and meta-analysis of the optimal clopidogrel loading dose. Pertinent trials comparing high (>300 mg) and standard (300 mg) clopidogrel loading doses in patients scheduled for catheterization and/or percutaneous coronary intervention were systematically searched in BioMedCentral, CENTRAL, Google Scholar, and PubMed (December 2006). The primary end point was the 1-month rate of death or myocardial infarction. Secondary end points included other ischemic and bleeding adverse effects. Peto odds ratios were computed. A total of 10 studies (7 randomized, 3 nonrandomized) were included, enrolling 1,567 patients (712 loaded with 300 mg, 11 with 450 mg, 790 with 600 mg, and 54 with 900 mg). Overall, a high loading dose proved significantly superior to a standard loading dose in preventing cardiac death or nonfatal myocardial infarction (odds ratio 0.54, 95% confidence interval 0.32 to 0.90, p = 0.02), without any statistically significant increase in major or minor bleedings (p = 0.55 and p = 0.98, respectively). Sensitivity analysis restricted to randomized trials confirmed the superiority of a high loading dose regimen (p = 0.0031). Meta-regression disclosed a significant interaction between event rate and the benefits of high loading doses (p = 0.005), suggesting that the greater the underlying risk, the greater the favorable impact of a high loading dose. In conclusion, a high clopidogrel loading dose (>300 mg) significantly reduces early ischemic events in patients scheduled for percutaneous coronary intervention.