In recent years, deep-sea fish oil is popular among the people because the advertisement says that it can prevent and treat cardiovascular diseases. In fact, this is wrong. The main active ingredient of fish oil is n-3 fatty acids, also called Omega-3 fatty acids, and its main efficacy is to partially reduce triglyceride levels, but it is not a medicine and cannot replace regular drugs. Several scientific studies have shown that taking fish oil does not reduce the occurrence of cardiovascular adverse events such as death, myocardial infarction and stroke. For people at high risk of cardiovascular and cerebrovascular disease, disease prevention should usually be achieved through a balanced diet structure, exercise, weight control, smoking cessation and alcohol restriction, and a healthy lifestyle. If triglycerides are increased, it is necessary to take fish oil through the above comprehensive measures, such as not lowering, adding beta lipid regulating drugs such as fenofibrate or statins such as atorvastatin and rasulvastatin, etc. It is ineffective and also delays diagnosis and treatment. If cardiovascular disease (e.g. coronary heart disease, cerebral infarction, etc.) has occurred, it must be treated with statins and not fish oil instead, as this will aggravate the condition. There is no medical research evidence to support that the combination of statins and fish oil reduces the occurrence of cardiovascular and cerebrovascular adverse events. In addition, fish oil has side effects. Taking large amounts of fish oil can lead to adverse digestive reactions and even liver damage. Therefore, it is more reliable not to blindly believe in advertisements, but to trust the words of doctors in regular hospitals.