Cod liver oil is a compound preparation of fat extracted from the liver of shark, cod, etc. It contains 1500 units of vitamin A and 150 units of vitamin D per gram. It is commonly used to prevent and treat pediatric rickets and night blindness and other vitamin AD deficiencies. When taken in accordance with the recommended dosage, it is generally safe and free from adverse reactions. Occasionally, cod liver oil has led to serious adverse reactions, and there have been reports of severe pain in the shoulder and knee joints caused by taking cod liver oil pills [1]. When taken for a long time or in excess, it can also produce chronic toxicity. Early manifestations include bone and joint pain, swelling, itchy skin, dry lips, weakness, fever, headache, vomiting, constipation, diarrhea, and nausea and vomiting. Vitamin A intake of more than 33,000 IU for a long time will cause chronic toxicity, baldness, movement disorders, pain, etc. Adults who consume more than 66,000 IU at one time will immediately experience vomiting and headache. Excess vitamin D can cause non-specific symptoms such as anorexia, weight loss, polyuria, cardiac arrhythmia, etc. More seriously it may cause calcification of blood vessels and tissues by raising blood calcium levels, damaging the heart, blood vessels and kidneys. Children and other people with a balanced diet and adequate outdoor activity do not need to take cod liver oil, and should be supplemented according to their precise needs as prescribed by their doctor.