Background: Deutetrabenazine is a vesicular monoamine transporter 2 inhibitor approved for the treatment of tardive dyskinesia (TD) in adults. In two 12-week pivotal studies, deutetrabenazine demonstrated statistically significant improvements in Abnormal Involuntary Movement Scale (AIMS) scores, with favorable safety/tolerability in TD patients. This study reports long-term efficacy and safety of deutetrabenazine in a 3-year, single-arm, open-label extension (OLE) study., Methods: Patients who completed the pivotal studies could enroll in this single-arm OLE study, titrating up to 48 mg/day based on dyskinesia control and tolerability. Efficacy was assessed based on change from baseline in total motor AIMS score, Clinical Global Impression of Change (CGIC) and Patient Global Impression of Change (PGIC), and quality of life (QOL) assessments. Safety evaluation included adverse event (AE) incidence, reported using exposure-adjusted incidence rates, and safety scales., Results: 343 patients enrolled in the study (6 patients were excluded). At Week 145 (mean dose: 39.4 ± 0.83 mg/day), mean ± SE change from baseline in total motor AIMS score was -6.6 ± 0.37 and 67% of patients achieved ≥50% improvement in total motor AIMS score. Based on CGIC and PGIC, 73% and 63% of patients achieved treatment success, respectively. QOL improvements were also observed. Deutetrabenazine was generally well tolerated, with low rates of mild-to-moderate AEs and no new safety signals; most safety scales remained unchanged over time., Conclusions: Long-term deutetrabenazine treatment was associated with sustained improvement in AIMS scores, indicative of clinically meaningful long-term benefit, and was generally well tolerated. Results suggest deutetrabenazine may provide increasing benefit over time without increases in dose., Competing Interests: RH has served as a consultant for Teva Pharmaceutical Industries, AbbVie Inc., Acorda Therapeutics, Adamas Pharmaceuticals, AstraZeneca, Biotie Therapies, Cynapsus Therapeutics, Impax Laboratories, Inc., Lundbeck LLC, the Michael J. Fox Foundation, Neurocrine Biosciences, Neuropore Therapies, Pfizer Inc., Prexton Therapeutics, US WorldMeds, Guidepoint Global, Gerson Lehrman Group, LCN Consulting, Putnam Associates, National Parkinson Foundation, eResearch Technology, Inc., Sarepta Therapeutics, Back Bay Life Science, National Institutes of Health (NIH), Projects in Knowledge, Vista Research, LifeMax, PeerView Press, ClinicalMind Medical and Therapeutic Communications, Sunovion Pharmaceuticals, Academy for Continued Healthcare Learning, Outcomes Insights, Expert Connect, HealthLOGIX, Cowen and Company, Pharma Two B Ltd., RMEI Medical Education for Better Outcomes, ClearView Healthcare Partners, Health Advances, Kyowa Kirin Pharmaceutical Development, Inc., Quintiles, and Eli Lilly and Company. HB is an employee of Teva Pharmaceutical Industries. HF has received honoraria from Prime Education, Inc., International Parkinson and Movement Disorders Society, Carling Communications, Medscape (speaker in CME events), AbbVie Inc., Biogen, GE Healthcare, inVentiv, Kyowa Hakko Kirin, Lundbeck LLC, Merz Pharmaceuticals, Voyager, Sunovion Pharmaceuticals, and Pfizer Inc. (as a consultant); grant and research support from AbbVie Inc., Acadia, Teva Pharmaceutical Industries, Biotie Therapies/Acorda Therapeutics, Civitas, Kyowa/ProStrakan, the Michael J. Fox Foundation, International Parkinson and Movement Disorders Society, NIH/NINDS, Parkinson Study Group, Rhythm, and Synosia; royalties from Demos Publishing (serving as a book author/editor); and a stipend from the International Parkinson and Movement Disorders Society (MDS) for serving as a medical editor of the MDS website. The Cleveland Clinic has a contract with Teva Pharmaceutical Industries for Dr. Fernandez's role as a co-principal investigator in SD-809 tardive dyskinesia global studies. HF also serves as a member of the publication committee for Acorda Therapeutics but does not receive any personal compensation for this work. HF has no owner interest in any pharmaceutical company. SF has received honoraria from Neurocrine Biosciences, Lundbeck LLC, Teva Pharmaceutical Industries, Avanir, UCB, US WorldMeds, Sunovion Pharmaceuticals, and Adamas Pharmaceuticals; research support from Ipsen, Medtronic, Auspex, US WorldMeds, Pharm-Olam, Cynapsus Therapeutics/Sunovion Pharmaceuticals, Vaccinex, Solstice, CHDI Foundation, the Michael J. Fox Foundation, and the NIH; and royalties from Demos and Blackwell Futura. JJ-S has received consulting fees from Medtronic, St. Jude Medical, Boston Scientific, Blue Rock Therapeutics, Bracket Global, Teva, Nuvelution, CNS Ratings, AbbVie, Spark Therapeutics, Revance, Amneal, and Impel. NG is an employee of Teva Pharmaceutical Industries. LM is an employee of Teva Pharmaceutical Industries. AW is a former employee of Teva Pharmaceutical Industries. JA is a former employee of Teva Pharmaceutical Industries. MG is an employee of Teva Pharmaceutical Industries. J-MS is a former employee of Teva Pharmaceutical Industries. KA has served as a scientific advisor for LEGATO-HD, AIM-TD, ARM-TD, ENROLL-HD, and Prana; site principal investigator for PRIDE-HD, First-HD, ARC-HD, ENROLL-HD, and Vaccinex; and consultant for the NeuroNEXT 105 study. KA has received salary support from the Griffin Foundation and honoraria from Vindico Medical Education. The authors declare that this study received funding from Teva Pharmaceutical Industries Ltd., Tel Aviv, Israel. The funder had the following involvement in the study: design, collection of data, analysis and interpretation of the data, review and drafting of the manuscript., (Copyright © 2022 Hauser, Barkay, Fernandez, Factor, Jimenez-Shahed, Gross, Marinelli, Wilhelm, Alexander, Gordon, Savola and Anderson.)