Background: Omega-3 polyunsaturated fatty acids (PUFAs) have some protective benefits for patients with coronary artery and cerebrovascular diseases. Eicosapentaenoic acid (EPA) drugs are prescribed as branded (B: EPADEL ®) or generic products but no data exist concerning the differences in treatment outcomes between these products. Methods and Results: We investigated the differences in the serum levels of EPA, docosahexaenoic acid (DHA) and arachidonic acid (AA), and the EPA/AA ratios through blood sampling six months after daily administration of 1800 mg of EPADEL ® and a generic EPA drug was initiated for 96 patients with cardiovascular diseases. All patients received these PUFA treatments while continuing with baseline therapy. After 6 months of administration, EPADEL ® produced better results than the generic (G) product (