Background: Olpasiran, a small interfering RNA (siRNA), blocks lipoprotein(a) (Lp(a)) production by preventing translation of apolipoprotein(a) mRNA. In phase 2, higher doses of olpasiran every 12 weeks (Q12W) reduced circulating Lp(a) by >95%., Objectives: This study sought to assess the timing of return of Lp(a) to baseline after discontinuation of olpasiran, as well as longer-term safety., Methods: OCEAN(a)-DOSE (Olpasiran Trials of Cardiovascular Events And LipoproteiN[a] Reduction-DOSE Finding Study) was a phase 2, dose-finding trial that enrolled 281 participants with atherosclerotic cardiovascular disease and Lp(a) >150 nmol/L to 1 of 4 active doses of olpasiran vs placebo (10 mg, 75 mg, 225 mg Q12W, or an exploratory dose of 225 mg Q24W given subcutaneously). The last dose of olpasiran was administered at week 36; after week 48, there was an extended off-treatment follow-up period for a minimum of 24 weeks., Results: A total of 276 (98.2%) participants entered the off-treatment follow-up period. The median study exposure (treatment combined with off-treatment phases) was 86 weeks (Q1-Q3: 79-99 weeks). For the 75 mg Q12W dose, the off-treatment placebo-adjusted mean percent change from baseline in Lp(a) was -76.2%, -53.0%, -44.0%, and -27.9% at 60, 72, 84, and 96 weeks, respectively (all P < 0.001). The respective off-treatment changes in Lp(a) for the 225 mg Q12W dose were -84.4%, -61.6%, -52.2%, and -36.4% (all P < 0.001). During the extension follow-up phase, no new safety concerns were identified., Conclusions: Olpasiran is a potent siRNA with prolonged effects on Lp(a) lowering. Participants receiving doses ≥75 mg Q12W sustained a ∼40% to 50% reduction in Lp(a) levels close to 1 year after the last dose. (Olpasiran Trials of Cardiovascular Events And LipoproteiN[a] Reduction-DOSE Finding Study [OCEAN(a)-DOSE]; NCT04270760)., Competing Interests: Funding Support and Author Disclosures The OCEAN(a)-DOSE study was funded by Amgen. Dr O’Donoghue has received grant funding through Brigham and Women’s Hospital from Novartis, Amgen, AstraZeneca, and Janssen; and has received honoraria from Novartis, Amgen, AstraZeneca, and Janssen. Dr Rosenson has received institutional grant funding from Amgen, Arrowhead, Lilly, Novartis, and Regeneron; has received consulting fees from Amgen, Arrowhead, CRISPER Therapeutics, Lilly, Novartis, Precision Biosciences, Regeneron, and Ultragenyx; has received nonpromotional speaker fees from Amgen and Kowa; and has held stock in MediMergent. Dr López is an employee of Amgen; and/or has owned Amgen stock or stock options. Dr Lepor has received grant support from Amgen, Novartis, Regeneron, New Amsterdam, Merck, Arrowhead, and AstraZeneca; and has received speaker and/or consulting fees from Amgen, Novartis, Regeneron, Merck, AstraZeneca, and Boehringer Ingelheim. Dr Baum has received consulting fees from Altimmune, Amgen, Axcella, Boehringer Ingelheim, Lilly, Esperion, Ionis, Madrigal, Merck, Novartis, and Regeneron; and has received speaker fees from Amgen, Lilly, and Regeneron. Dr Gaudet has received grants and personal fees from Amgen during the conduct of the study; has received grants from Acasti, Kowa, Uniqure, Sanofi, Aegerion, Applied Therapeutics, AstraZeneca, Boehringer Ingelheim, Ceapro, Dalcor, Esperion, Arrowhead, Regeneron, Akcea, Allergan, Amryt, Ionis, Novartis, Novo Nordisk, Pfizer, Lilly, and The Medicine Company, outside the submitted work; and has received personal fees from Arrowhead, Regeneron, Akcea, Allergan, Amryt, Ionis, Novartis, Novo Nordisk, Pfizer, Lilly, CRISPR Therapeutics, Saliogen, and Ceapro, outside the submitted work. Dr Knusel is an employee of Amgen; and/or has owned Amgen stock or stock options. Ms Kuder has served as a member of the TIMI Study Group, which has received institutional research grant support through Brigham and Women’s Hospital from Abbott, Amgen, Anthos Therapeutics, AstraZeneca, Bayer HealthCare Pharmaceuticals, Daiichi-Sankyo, Eisai, Intarcia, MedImmune, Merck, Novartis, Pfizer, Quark Pharmaceuticals, Regeneron, Roche, Siemens Healthcare Diagnostics, The Medicines Company, and Zora Biosciences. Ms Murphy has served as a member of the TIMI Study Group, which has received institutional research grant support through Brigham and Women’s Hospital from Abbott, Amgen, Anthos Therapeutics, AstraZeneca, Bayer HealthCare Pharmaceuticals, Daiichi-Sankyo, Eisai, Intarcia, MedImmune, Merck, Novartis, Pfizer, Quark Pharmaceuticals, Regeneron, Roche, Siemens Healthcare Diagnostics, The Medicines Company, and Zora Biosciences. Dr H. Wang is an employee of Amgen; and/or has owned Amgen stock or stock options. Dr Wu is an employee of Amgen; and/or has owned Amgen stock or stock options. Dr Shah is an employee of Amgen; and has owned Amgen stock. Dr J. Wang is an employee of Amgen; and has owned Amgen stock. Dr Wilmanski is an employee of Amgen; and has owned Amgen stock. Dr Sohn is an employee of Amgen; and/or has owned Amgen stock or stock options; and has existing or pending patents related to olpasiran. Dr Kassahun is an employee of Amgen; and/or has owned Amgen stock or stock options; and has existing or pending patents related to olpasiran. Dr Sabatine has received research grant support through Brigham and Women’s Hospital from Abbott, Amgen, Anthos Therapeutics, Inc, AstraZeneca, Boehringer Ingelheim, Daiichi-Sankyo, Ionis, Merck, Novartis, Pfizer, Saghmos Therapeutics, and Verve Therapeutics; has served as a consultant for Amgen, AMPEL BioSolutions, Anthos Therapeutics, Inc, AstraZeneca, Beren Therapeutics, Boehringer Ingelheim, Dr Reddy’s Laboratories, Fibrogen, Merck, Moderna, Novo Nordisk, Precision BioSciences, and Silence Therapeutics; and has served as a member of the TIMI Study Group, which has also received institutional research grant support through Brigham and Women’s Hospital from ARCA Biopharma, Janssen Research and Development, Siemens Healthcare Diagnostics, Softcell Medical Limited, Regeneron, Roche, and Zora Biosciences. Dr Stout has reported that he has no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)