Study Objectives: Solriamfetol, a dopamine/norepinephrine reuptake inhibitor, is approved in the United States and European Union for excessive daytime sleepiness in adults with narcolepsy (75-150 mg/day) or obstructive sleep apnea (OSA; 37.5-150 mg/day). In 12-week studies, solriamfetol was associated with improvements in quality of life in participants with narcolepsy or OSA. These analyses evaluated the long-term effects of solriamfetol on quality of life. Methods: Participants with narcolepsy or OSA who completed previous solriamfetol studies were eligible. A 2-week titration was followed by a maintenance phase ≤ 50weeks (stable doses: 75, 150,or 300mg/day). Quality oflife assessments included Functional Outcomes of Sleep Questionnaireshort version, WorkProductivity and Activity Impairment Questionnaire: Specific Health Problem, and 36-Item Short Form Health Survey version 2. Mean (standard deviation) changes from baseline to end of study were evaluated. Data were summarized descriptively. Adverse events were assessed. Results: Safety population comprised 643 participants (417 OSA, 226 narcolepsy). Solriamfetol improved Functional Outcomes of Sleep Questionnaire short version Total scores (mean change [standard deviation], 3.7 [3.0]) and 36-Item Short Form Health Survey version 2 Physical and Mental Component Summary scores (3.1 [6.9] and4.3 [8.4], respectively); improvements were sustained throughout treatment. On WorkProductivity and Activity Impairment Questionnaire: Specific Health Problem, solriamfetol reduced (improved) % presenteeism, % overall work impairment, and % activity impairment by a minimum of 25%. Common adverse events (≥ 5%): headache, nausea, nasopharyngitis, insomnia, dry mouth, anxiety, decreased appetite, and upper respiratory tract infection. Conclusions: Long-term solriamfetol treatment was associated with clinically meaningful, sustained improvements in functional status, work productivity, and quality of life for up to 52 weeks. Adverse events were similar between narcolepsy and OSA.