Laxatives are drugs that increase water in the intestine, promote peristalsis, soften stool or lubricate the intestine to facilitate defecation. They are mainly used clinically for functional constipation and are divided into three categories: volumetric, stimulant and lubricating laxatives. What are the common clinical laxatives? A, volumetric laxatives non-absorbable salts magnesium sulfate and sodium sulfate also known as salt laxatives. In the intestinal tract is difficult to absorb, a large number of oral formation of hypertonic pressure and prevent the absorption of water in the intestine, dilate the intestine, stimulate the intestinal wall, promote intestinal peristalsis. In addition, magnesium salt can also cause the duodenum to secrete cholecystokinin, this hormone can stimulate intestinal fluid secretion and peristalsis. General fasting application, and drink a lot of water, 1 to 3 hours that the diarrheal effect, the discharge of liquid stool. The diarrhea inducing effect is strong, so the clinical mainly used to exclude intestinal toxins and certain intestinal worm medicine after taking the worm with the drug. Magnesium sulfate, sodium sulfate diarrhea effect is more intense, can cause reflex pelvic congestion and water loss. Menstruation, pregnant women and the elderly use with caution. Dietary fiber and other substances 1. Lactulose is a disaccharide of galactose and fructose. It is not digested and absorbed in the small intestine, so it can induce diarrhea. The unabsorbed part enters the colon and is metabolized by bacteria into lactic acid, etc., which further increases the intestinal osmotic pressure and causes light diarrhea. Lactulose can also lower the pH of the colon contents and reduce the formation of ammonia in the intestine; H+ can also form ammonium ions with the generated ammonia and not be absorbed, thus reducing blood ammonia. It can be used for chronic portal hypertension and hepatic encephalopathy. It should be noted that the loss of water and electrolytes due to diarrhea can worsen hepatic encephalopathy. 2.Food fiber. Including natural and semi-synthetic polysaccharides and cellulose derivatives in vegetables and fruits, such as methyl cellulose, carboxymethyl cellulose, etc. are not absorbed by the intestinal tract, increasing intestinal volume and keeping stool wet and soft, with good laxative effect. Can prevent and control functional constipation. Second, contact laxatives old name “stimulant laxatives”. Can affect intestinal activity and absorption of water and electrolytes in the intestinal mucosa and cause diarrhea of a class of drugs. Including anthraquinones and diphenylmethanes, such as rhubarb, senna and aloe vera and other plant laxatives contain anthraquinone glycosides. The main effect on the large intestine, no effect on the small intestine absorption function, so it can be used for acute and chronic constipation. 1, phenolphthalein. After oral administration, it meets with alkaline intestinal fluid to form soluble sodium salts in the intestine, which can promote colon peristalsis and excrete soft stools 6-8 hours after taking the drug, with mild effect, suitable for chronic constipation. About 15% of oral phenolphthalein is absorbed. Phenolphthalein is excreted from urine, if urine is alkaline then it is red, partly excreted by bile, and there is hepatic and intestinal circulation to prolong its action, so the effect of one dose can be maintained for 3 to 4 days. In case of anaphylactic reaction, enteritis, dermatitis and bleeding tendency will occur. Pisacodyl is used for constipation or X-ray, endoscopy or pre-operative evacuation of intestinal contents. 2, anthraquinones. Rhubarb, senna and aloe vera and other plants, containing anthraquinone glycosides, orally decomposed into anthraquinone by bacteria in the large intestine, can increase the colon propulsive motility. 6 to 8 hours after the drug defecation, commonly used in acute and chronic constipation. Third, lubricating laxatives lubricating laxatives is through the local slippery and soften the stool and play a role. Suitable for the elderly and hemorrhoids, anal surgery patients. 1, liquid paraffin. For mineral oil, not digested and absorbed by the intestine, produce the effect of slippery intestinal wall and softening stool, so that the stool is easy to pass. 2.Glycerin. Injected into the anus with a 50% concentration of liquid, it stimulates the intestinal wall to cause a defecation response due to high osmolarity and has a local lubricating effect, causing defecation within a few minutes. Can be applied to children and the elderly.