BACKGROUND: Little is known about medication adherence patterns and their association with effectiveness and safety among patients with venous thromboembolism (VTE) receiving direct oral anticoagulant (DOAC) therapy beyond 3-6 months of initial treatment. OBJECTIVE: To examine the associations between adherence trajectories of extended treatment with DOAC and the risks of recurrent VTE and major bleeding among patients with VTE. METHODS: We conducted a retrospective cohort study of patients with incident VTE who completed 6 months of initial anticoagulant treatment and received either DOAC extended therapy or no extended therapy using MarketScan Commercial and Medicare Supplemental databases (2013-2019). We used group-based trajectory models to identify distinct adherence patterns during extended treatment. Using inverse probability treatment weighted Cox proportional hazards models, we examined the association between the adherence trajectories and the risks of recurrent VTE and major bleeding. RESULTS: Among 10,960 patients with extended treatment with DOACs (rivaroxaban, apixaban, dabigatran, edoxaban) and 5,133 patients with no extended treatment, we identified 4 distinct trajectories (consistently high, gradually declining, rapidly declining, and no extended treatment). Compared with the no extended treatment group, the groups with consistently high adherence (hazard ratio = 0.09, 95% CI = 0.05-0.17) and with gradually declining adherence (0.13, 0.03-0.53) showed decreased recurrent VTE risk without increased major bleeding risk (consistently high adherence 1.19, 0.71-1.99; gradually declining adherence 1.96, 0.81-4.70). There was no difference in the risk of recurrent VTE (0.34, 0.10-1.16) for the group with rapidly declining adherence, but this group was associated with increased major bleeding risk (2.65, 1.01-6.92). CONCLUSIONS: Our findings underscore the clinical importance of continuing and remaining adherent to extended DOAC treatment without increased major bleeding risk for patients with VTE. DISCLOSURES: This research was supported by the BMS/Pfizer Alliance American Thrombosis Investigator Initiated Research Program. The funding source had no role in the design, collection, analysis, or interpretation of the data or the decision to submit the article for publication. Dr Lo-Ciganic reported receiving research funding from Merck Sharp & Dohme Corp. Dr Dietrich reported receiving honorarium for training and education from BMS/Pfizer. Dr DeRemer is a stockholder of Portola Pharmaceuticals and reported receiving personal fees for advisory board meeting from BMS. No other disclosures were reported.