• Janelle M Guirguis-Blake, Corinne V Evans, Leslie A Perdue, Sarah I Bean, and Caitlyn A Senger.
• Kaiser Permanente Evidence-based Practice Center, Center for Health Research, Kaiser Permanente, Portland, Oregon.
• JAMA. 2022 Apr 26; 327 (16): 1585-1597.

ImportanceLow-dose aspirin is used for primary cardiovascular disease prevention and may have benefits for colorectal cancer prevention.ObjectiveTo review the benefits and harms of aspirin in primary cardiovascular disease prevention and colorectal cancer prevention to inform the US Preventive Services Task Force.Data SourcesMEDLINE, PubMed, Embase, and the Cochrane Central Register of Controlled Trials through January 2021; literature surveillance through January 21, 2022.Study SelectionEnglish-language randomized clinical trials (RCTs) of low-dose aspirin (≤100 mg/d) compared with placebo or no intervention in primary prevention populations.Data Extraction And SynthesisSingle extraction, verified by a second reviewer. Quantitative synthesis using Peto fixed-effects meta-analysis.Main Outcomes And MeasuresCardiovascular disease events and mortality, all-cause mortality, colorectal cancer incidence and mortality, major bleeding, and hemorrhagic stroke.ResultsEleven RCTs (N = 134 470) and 1 pilot trial (N = 400) of low-dose aspirin for primary cardiovascular disease prevention were included. Low-dose aspirin was associated with a significant decrease in major cardiovascular disease events (odds ratio [OR], 0.90 [95% CI, 0.85-0.95]; 11 RCTs [n = 134 470]; I2 = 0%; range in absolute effects, -2.5% to 0.1%). Results for individual cardiovascular disease outcomes were significant, with similar magnitude of benefit. Aspirin was not significantly associated with reductions in cardiovascular disease mortality or all-cause mortality. There was limited trial evidence on benefits for colorectal cancer, with the findings highly variable by length of follow-up and statistically significant only when considering long-term observational follow-up beyond randomized trial periods. Low-dose aspirin was associated with significant increases in total major bleeding (OR, 1.44 [95% CI, 1.32-1.57]; 10 RCTs [n = 133 194]; I2 = 4.7%; range in absolute effects, 0.1% to 1.0%) and in site-specific bleeding, with similar magnitude.Conclusions And RelevanceLow-dose aspirin was associated with small absolute risk reductions in major cardiovascular disease events and small absolute increases in major bleeding. Colorectal cancer results were less robust and highly variable.

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