Fish oil supplements containing the omega-3 fatty acids eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) are commonly taken to prevent or reduce complications of heart disease.

A 2017 American Heart Association Science Advisory noted that omega-3 fish oil supplements prescribed by a health care professional may help prevent death from heart disease in patients who recently had a heart attack and may prevent death and hospitalizations in patients with heart failure. However, there is a lack of scientific research to support clinical use of these supplements to prevent heart disease in the general population.

"Many people continue to take fish oil supplements to prevent heart disease. However, the fish oil medication we tested in the STRENGTH trial was not effective for that purpose," said lead author A. Michael Lincoff, M.D., vice chairman for Research of the Department of Cardiovascular Medicine and an interventional cardiologist in the Heart, Vascular & Thoracic Institute at the Cleveland Clinic.

"We believe the questions surrounding the benefit versus risk of fish oil will remain unanswered unless another trial using a neutral placebo such as corn oil is able to definitively show cardiovascular benefits for an omega-3 fatty acid medication," he said.

This phase III international study evaluated omega-3 CA in 13,078 adults at 675 centers in 22 countries. The patients were all being treated with cholesterol-lowering statins and had either blockages of the arteries to the heart, brain or legs or were at increased risk for heart disease due to other medical conditions such as diabetes or lifestyle risk factors such as smoking.

Participants were randomly assigned to receive either 4 grams of the omega-3 CA medication or the corn oil placebo daily. Researchers compared the rate of cardiovascular death, heart attack, stroke, need for coronary revascularization (stenting or bypass surgery) or hospitalization for unstable angina for all patient groups.

The study began in 2014 and was stopped slightly early, in January 2020, because preliminary results of the study deemed it unlikely to prove the benefit omega-3 CA medication. Over a median follow up time of about three years, 1,580 patients experienced at least one cardiac event. There were no significant differences in the number of patients experiencing cardiac events between the two treatment groups. Additionally, a potentially dangerous abnormal heart rhythm (atrial fibrillation) occurred more frequently among patients taking the omega-3 CA medication than in those receiving the control corn oil.