ObjectivesTo systematically review the safety and efficacy of aspirin in primary prevention of cardiovascular diseases.MethodsPubMed, EMbase, Web of Science, The Cochrane Library, CBM, WanFang Data, CNKI and VIP databases were electronically searched to collect randomized controlled trials (RCTs) of aspirin for primary prevention of cardiovascular diseases from inception to November 2018. Two reviewers independently screened literature, extracted data and assessed the risk of bias of included studies, and then, meta-analysis was performed by RevMan 5.3 software.ResultsA total of 13 RCTs involving 164 225 participants were included. The results of meta-analysis showed that: aspirin reduced the risk of myocardial infarction (RR=0.85, 95%CI 0.75 to 0.97, P=0.01), ischemic stroke (RR=0.86, 95%CI 0.79 to 0.95, P=0.002) and risk of major adverse cardiovascular events (RR=0.90, 95%CI 0.86 to 0.94, P<0.000 1). However, all-cause mortality (RR=0.97, 95%CI 0.93 to 1.02, P=0.22) and cardiovascular mortality (RR=0.93, 95%CI 0.85 to 1.02, P=0.11) were not reduced. Additionally, it increased risk of hemorrhagic stroke (RR=1.29, 95%CI 1.02 to 1.64, P=0.03), major bleeding (RR=1.43, 95%CI 1.31 to 1.56, P<0.000 01) and gastrointestinal bleeding (RR=1.59, 95%CI 1.33 to 1.90, P<0.000 01).ConclusionCurrent evidence shows that aspirin can reduce the incidence of major adverse cardiovascular events and myocardial infarction during primary prevention of cardiovascular disease, while increase the risk of bleeding, especially gastrointestinal bleeding. Therefore, its potential benefits may be offset. Due to limited quality and quantity of the included studies, more high-quality studies are required to verify the above conclusion.