A diet including fatty fish or fish oil supplements is often recommended to help lower cholesterol and reduce the risk of heart disease. Fish oil supplements are sold over the counter, and prescription products are also available. The components in fish oil that are beneficial are omega-3 fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
Prescription omega-3 fatty acid products are subject to higher standards of safety, purity and efficacy than are the over the counter supplements and have been approved for lowering triglyceride levels. OTC supplements may contain variable amounts of EPA and DHA and can also contain other contaminants.
EPA and DHA are effective at reducing triglycerides, but can increase LDL-cholesterol, the bad cholesterol, so some patients may need additional treatment that targets other components of cholesterol. Omega-3 fatty acids have other effects that make them beneficial for patients with heart disease. They can improve blood flow and decrease platelet aggregation, reduce the growth of plaques in the blood vessels, dilate blood vessels, and reduce blood pressure. More here
The American Heart Association recommends eating fatty fish twice a week, including salmon, mackerel, herring, tuna and sardines. This may not provide enough omega-3 fatty acids for patients with coronary artery disease, so a supplement may help. Ask your doctor before starting any supplements.
For more ways to lower cholesterol see https://health.clevelandclinic.org/from-fiber-to-fish-oil-natural-ways-to-lower-your-cholesterol/