For patients with chronic constipation for a long time, it is not advisable to use stimulating laxatives in large quantities for a long time, because drugs can damage nerve plexus cells in intestinal wall and cause further constipation. Lactulose is an osmotic laxative, which can be used to treat chronic functional constipation because it has no intestinal irritation. Glycerol is a lubricating laxative, which is forbidden for diabetics. Irritating laxatives can increase intestinal peristalsis and often cause abdominal pain. Patients with intestinal obstruction should be banned. Lactulose is prohibited in patients with lactic acidemia. Therefore, this topic chooses ABCDE.