Patients with constipation generally need 0.5-3 hours to defecate after taking lactulose orally, and the specific defecation time is related to the patient’s physical condition. Lactulose has a laxative effect and constipation can be treated by taking lactulose orally. The onset of action varies from person to person, with some patients responding faster to lactulose and having a bowel movement in half an hour, while some patients may take 2-3 hours to have a bowel movement. In addition, the dose of lactulose is also an influencing factor on the time to effect after taking lactulose orally. Patients who take a high dose will have a fast effect time, while those who take an insufficient dose may show ineffective performance. When taking lactulose for constipation, the cause of constipation should be clarified. Lactulose is prohibited for patients with intestinal obstruction and acute abdomen, and should also be used with caution for patients taking other laxatives. In addition, try to avoid long-term use of lactulose, as it may aggravate the symptoms of constipation.