Their paper, presented at the 58th conference of the American College of Cardiology, found fish oil omega-3 supplements had no more benefit for patients already taking pharmaceuticals for heart conditions, than placebo.

Despite the apparently negative results, the researchers did not condemn fish oil supplementation, noting the study did not have as an aim, whether fish oil can prevent the onset of heart disease in the first place.

The American Heart Association recommends that coronary heart disease patients take a gram of omega-3s per day, and recommends 2 to 4 grams per day to patients needing to lower triglyceride levels.

The high-dose omega-3, prescription form used in the trial is sold as Omacor and Lovaza in the US and Zodin in Europe.