There are many causes of poor liver function, and some of the most common ones are described below.
1. Hepatitis. 
Hepatitis is one of the leading causes of poor liver function. There are two types of hepatitis: viral hepatitis and non-viral hepatitis. Viral hepatitis, including hepatitis B virus (HBV), hepatitis C virus (HCV), etc., can cause damage to the liver and lead to abnormal liver function.
2. Alcoholism. Long-term alcohol abuse can cause serious damage to the liver, leading to diseases such as fatty liver, alcoholic hepatitis, and cirrhosis. Alcohol destroys liver cells, leading to impaired liver cell function.
3. Obesity. Obesity is one of the main causes of hepatic steatosis, which is the deposition of fat within the liver, resulting in abnormal liver function. Obesity is also associated with diseases such as high blood pressure, hyperlipidemia, and diabetes, which can also increase the burden on the liver.
4. Drugs and poisons.
Long-term use of certain medications, such as analgesics, antibiotics, anticancer drugs, etc., can have adverse effects on the liver, resulting in abnormal liver function. In addition, certain poisons, such as organic solvents, heavy metals, etc., can also impair liver function.
5. Autoimmune diseases.
Autoimmune diseases, such as autoimmune hepatitis, primary biliary cirrhosis, etc., can cause liver damage, which in turn affects liver function.
6. Genetic factors.
Certain inherited liver diseases, such as cirrhosis and polycystic liver disease, can cause abnormal liver function. These liver diseases may be due to genetic mutations that cause abnormalities in liver structure and function.
In summary, the causes of poor liver function include viral infections, alcoholism, obesity, the effects of drugs and poisons, autoimmune diseases, and genetic factors, among others. In order to protect liver health, it is necessary to stay away from alcohol, eat a reasonable diet, exercise moderately, avoid drug abuse, and have regular medical check-ups to detect and deal with possible problems early. If you have symptoms of abnormal liver function, you should seek medical advice in time.