BACKGROUND: Although metformin is generally universally recommended as a first-line pharmacologic therapy for most people living with type 2 diabetes, second-line and third-line choices can require a tailored approach to achieve optimal blood glucose and glycated hemoglobin levels. OBJECTIVE: To examine national trends in second- and third-line antihyperglycemic medications following metformin monotherapy, comparing 2015 and 2019. METHODS: This retrospective cohort analysis of deidentified pharmacy claims from a large national pharmacy benefits manager from January 1, 2015, to December 31, 2015, and again in January 1, 2019, to December 31, 2019, included adults (aged ≥ 18 years) continuously enrolled in commercial or Medicare insurance plans who filled an index metformin prescription in either year. Proportions of patients by second-line and third-line antihyperglycemic class were calculated. RESULTS: Second-line use of sulfonylureas (-10.1%; P < 0.001), combination drugs (-3.0%; P < 0.001), and dipeptidyl peptidase-4 inhibitors (-2.0%; P = 0.031) significantly declined, whereas second-line use of sodium-glucose cotransporter 2 inhibitors (SGLT2is) (+4.9%; P < 0.001) and glucagon-like peptide-1 receptor agonists (GLP-1Ras) (+10.0%; P < 0.001) significantly increased. Similarly, third-line use of sulfonylureas declined (-5.5%; P = 0.005), whereas third-line use of SGLT2is (+3.4%; P = 0.005) and GLP-1RAs (+8.3%; P < 0.001) increased. Similar trends between 2015 and 2019 were found in commercial and Medicare subgroups. Among all groups in 2015 compared with 2019, sulfonylureas were the most prescribed second-line class and insulins the most common third-line class. Although SGLT2i and GLP-1RA together represented more than one-third of second-line and third-line prescriptions for commercially insured patients in 2019 (34.3% and 35.0%, respectively), these classes were less frequently prescribed in the Medicare subgroup (18% and 25.6%, respectively). CONCLUSIONS: This report provides updated second-line and third-line antihyperglycemic medication prescribing trends in the United States, which suggests that evidence-based guidelines are being used in practice to prevent complications and individualize diabetes care. DISCLOSURES: Ms Swart and Drs Peasah and Good are employed by UPMC Health Plan. Dr Neilson was employed by UPMC Health Plan at the time of the study. Drs Munshi and Henderson were employed by Evernorth at the time of the study.