Lipid-lowering therapy (LLT) is the cornerstone for secondary prevention of atherosclerotic cardiovascular disease (ASCVD); however, many patients exhibit low adherence to therapy and fail to achieve low-density lipoprotein cholesterol (LDL-C) goals. This retrospective cohort study used 2 nationally representative closed administrative claims databases (PharMetrics Plus and Medicare Fee-for-Service Research Identifiable Files) to identify commercial and Medicare enrollees with ASCVD between 2014 and 2019. Patients were stratified by exposure to statin therapy, ezetimibe, and proprotein convertase subtilisin/kexin type 9 inhibitor monoclonal antibodies (PCSK9i mAb) regimens. Outcomes included LLT adherence (proportion of days covered ≥0.8), persistence, and discontinuation at 12 months. For patients with LDL-C test results, the percentage of patients achieving LDL-C <70 mg/100 ml during follow-up was evaluated. We identified 4.6 million patients with ASCVD (commercial: 945,704; Medicare: 3,659,011), with the majority having ischemic or coronary heart disease. Of these, 66.4% commercial and 71.4% Medicare patients were on at least 1 LLT, including 69.8% commercial and 71.4% Medicare patients on statin therapy, 2.7% commercial and 1.7% Medicare patients on ezetimibe, and 0.2% commercial and 0.04% Medicare patients on a PCSK9i mAb. By 12 months, medication discontinuation was as follows: 30.4% commercial and 34.1% Medicare for statin therapy, 35.5% commercial and 46.1% Medicare for ezetimibe, and 41.5% commercial and 55.8% Medicare for PCSK9i mAb. Approximately half of the treated patients remained adherent after 12 months. Of patients with LDL-C data available (n = 381,160), <20% achieved an LDL-C <70 mg/100 ml. In conclusion, medication discontinuation and low adherence to statin, ezetimibe, and PCSK9i mAb therapies were observed in both populations. Increased efforts are needed to ensure persistence and adherence to LLT in patients with ASCVD to attain LDL-C targets.