This Phase 3 study will evaluate the efficacy of AKCEA‑APOCIII‑LRx on the percent change in fasting triglycerides (TGs). The drug is based on antisense technology, which is a therapy for reducing disease-causing proteins before they even begin. The study therapy (called AKCEA‑APOCIII‑LRx) is designed to target and reduce the activity of a protein in the body. Targeting this protein may help break down dietary fat and a clinically relevant reduction in triglycerides. The study drug therapy (investigational drug or placebo) will be administered as a subcutaneous injection (an injection under your skin).