OBJECTIVE: Estimates of prevalence and burden of treatment-resistant depression (TRD) vary widely in the literature. This study evaluated the prevalence and burden of TRD and the share of TRD in the burden of medication-treated major depressive disorder (MDD) using the most commonly accepted definition of TRD and a novel bottom-up approach. METHODS: Prevalence and health care burden of TRD were estimated by synthetizing inputs across 4 similarly designed claims studies in adults covered by Medicare, Medicaid, commercial plans, and the US Veterans Health Administration (VHA). Productivity (absenteeism and presenteeism) and unemployment burden were estimated based on inputs from a study conducted with data from the Kantar National Health and Wellness Survey (NHWS; 2017). A targeted literature search for additional inputs was performed. A cost model was developed to estimate the burden of TRD and medication-treated DSM-5-defined MDD in the United States. Study outcomes were the 12-month prevalence of TRD and the annual health care, productivity, and unemployment burden of TRD and medication-treated MDD in the United States. RESULTS: The estimated 12-month prevalence of medication-treated MDD in the United States was 8.9 million adults, and 2.8 million (30.9%) had TRD. The total annual burden of medication-treated MDD among the US population was $92.7 billion, with $43.8 billion (47.2%) attributable to TRD. The share of TRD was 56.6% ($25.8 billion) of the health care burden, 47.7% ($8.7 billion) of the unemployment burden, and 32.2% ($9.3 billion) of the productivity burden of medication-treated MDD. CONCLUSIONS: TRD is associated with disproportionate health care costs and unemployment, suggesting potentially large economic and societal gains with effective management.