The purpose of this study is to evaluate the efficacy of olezarsen as compared to placebo on the percent change in fasting triglycerides (TG) from baseline.

This is a Phase 3, multi-center, randomized, double-blind, placebo-controlled study in 446 participants. Participants will be randomized to receive olezarsen or placebo in a 53-week treatment period. The length of participation in the study will be approximately 78 weeks, which includes an up to 12-week screening period, a 53-week treatment period, and a 13-week post-treatment evaluation period or transition to open-label extension (OLE) study with up to 1-year treatment.

Inclusion Criteria:

1. Fasting TG ≥ 500 mg/dL (5.65 mmol/L) at Screening and Qualification
2. Participants must be on lipid-lowering therapy that should adhere to standard of care (SOC) per local guidelines. Lipid-lowering medications should be optimized and stabilized for at least 4 weeks prior to screening to minimize changes in these medications during the study.
3. Participants must be willing to comply with diet and lifestyle recommendations as able.

Exclusion Criteria:

1. Hemoglobin A1c (HbA1c) ≥ 9.5% at Screening
2. Alanine aminotransferase or aspartate aminotransferase > 3.0 × upper limit of normal
3. Total bilirubin > 1.5 ULN unless due to Gilbert's syndrome
4. Estimated GFR < 30 mL/min/1.73 m^2

Ionis may share anonymized individual participant data, aggregated clinical data, and other types of data that support the results in this study. Data requests from qualified researchers will be considered once all three of the following criteria are met: (1) 12 months from marketing approval of the study drug in both the United States and European Union; (2) 18 months from conclusion of the study; and (3) 6 months from publication of study article. Access would be via a secure environment and is contingent upon approval of a research proposal and entry into an appropriate data use agreement. Requests to access data can be submitted via the website https://vivli.org/ourmember/ionis/.