I was impressed to see this by the website examine.com which I regularly visit to dig deep on certain supplements
Safety Spotlight: Omega-3 fatty acid supplementation can increase the risk of atrial fibrillation
"The heart health benefits of omega-3 fatty acid supplementation have been recently brought into question, with two high-dose trials coming to dramatically different conclusions. On one hand, REDUCE-IT[1]found that 4 grams daily of pharmaceutical-grade EPA reduced the risk of cardiovascular events in people at high risk and with elevated triglyceride levels compared to a mineral oil placebo. On the other hand, STRENGTH[2] found that 4 grams daily of a pharmaceutical-grade mixture of roughly 2:1 EPA/DHA had no positive effect compared to a corn oil placebo. While these two landmark trials disagreed about the cardiovascular benefits of omega-3s, they did agree about one of its possible harms: that supplementation can increase the risk of atrial fibrillation."
Anyone else find it funny that they consider mineral oil a placebo... anyway here is the article in full.