When cirrhosis is complicated by hepatic encephalopathy, symptoms of abnormal cognitive function, commonly known as brain fog, can occur. Ammonia toxicity is an important pathogenesis of hepatic encephalopathy, and the digestive tract is the main site of ammonia production by the body, including nonionic and ionic ammonia. In cirrhosis, the liver’s metabolism of nonionic ammonia decreases, and the concentration of nonionic ammonia in the circulation increases. Non-ionic ammonia can cross the blood-brain barrier and enter the brain tissue to interfere with brain function, resulting in hepatic encephalopathy. The manifestation of hepatic encephalopathy may progress from normal cognitive function to abnormal cognitive function or even coma, which is actually a manifestation of the disease to the general public who think that the brain is confused. Once hepatic encephalopathy develops, it needs to be treated in a timely manner, otherwise it may lead to aggravation of the condition or even become life-threatening.