Methods of identifying subjects who are resistant to antiplatelet therapy, such as therapy with clopidogrel, are presented. The methods comprise determining is whether the subject is an efficient converter of medium chain polyunsaturated fatty acids to long-chain polyunsaturated fatty acids. Also provided are methods of treating resistance to antiplatelet therapy in subjects who are efficient converters of medium chain polyunsaturated fatty acids to long-chain polyunsaturated fatty acids, comprising adjunctively administering to the subject an effective amount of a composition comprising omega-3 long chain polyunsaturated fatty acids. Improved methods of antiplatelet therapy are provided, wherein the improvement comprises adjunctive administration of a composition comprising omega-3 long chain polyunsaturated fatty acids in free acid form. Dosage forms comprising at least one antiplatelet agent and compositions comprising omega-3 long chain polyunsaturated fatty acids, including compositions comprising omega-3 long chain polyunsaturated fatty acids in free acid form, are provided.
