text: The US National Institutes of Health lists three conditions for which fish oil and other omega-3 sources are most highly recommended: hypertriglyceridemia (high triglyceride level), preventing secondary cardiovascular disease, and hypertension (high blood pressure). It then lists 27 other conditions for which there is less evidence. It also lists possible safety concerns: "Intake of 3 grams per day or greater of omega-3 fatty acids may increase the risk of bleeding, although there is little evidence of significant bleeding risk at lower doses. Very large intakes of fish oil or omega-3 fatty acids may increase the risk of hemorrhagic (bleeding) stroke."
  There were studies to determine if fish oil had an effect on certain abnormal heart rhythms, although a 2012 meta-analysis found no significant effect.
  A 2008 meta-study found fish oil supplementation did not demonstrate any preventative benefit to cardiac patients with ventricular arrhythmias. A 2012 meta-analysis  covering 20 studies and 68,680 patients, found that omega-3 fatty acid supplementation did not reduce the chance of death, cardiac death, heart attack, or stroke. A 2018 meta-analysis of 77,000 participants found a 3% reduction in the relative risk for those who supplemented fish oil; however, this effect was deemed insignificant.
  Hypertension
  There have been some human trials that have concluded that consuming omega-3 fatty acids slightly reduces blood pressure (DHA could be more effective than EPA). Because omega-3 fatty acids can increase the risk of bleeding, a qualified healthcare provider should be consulted before supplementing with fish oil.
  Mental health
  A 2008 Cochrane systematic review found that limited data is available. In the one eligible study, omega-3s were an effective adjunctive therapy for depressive but not manic symptoms in bipolar disorder. The authors found an "acute need" for more randomised controlled trials.