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Drug Profile

The information on this site is intended to supplement and enhance, not replace, the advice of a physician who is familiar with your medical history. Decisions about your health should always be made ONLY after detailed conversation with your doctor.

Limited Use [what does this mean?]
Generic drug name: lactulose (LAK tu lose)
Brand name(s): CEPHULAC, CHRONOLAC
GENERIC: available FAMILY: Drugs for Constipation
Find the drug label by searching at DailyMed.

Pregnancy and Breast-feeding Warnings [top]

Pregnancy Warning

No valid data are available for lactulose, as it was not tested properly in animal studies. Use during pregnancy only for clear medical reasons. Tell your doctor if you are pregnant or thinking of becoming pregnant before you take this drug.

Breast-feeding Warning

No information is available from either human or animal studies. Since it is likely that this drug, like many others, is excreted in human milk, you should consult with your doctor if you are planning to nurse.

Facts About This Drug [top]

Lactulose is a synthetic combination of the sugars galactose and fructose. It is not well absorbed from the intestines, and the body responds by secreting water into the intestines. Drugs that reduce constipation this way are called hyperosmotic laxatives. The sugars are also fermented by bacteria in the colon, producing hydrogen gas. (Patients taking the laxatives psyllium or methycellulose  appear to be less likely to pass gas than those taking lactulose.[1]) Both actions expand the colon,...

Lactulose is a synthetic combination of the sugars galactose and fructose. It is not well absorbed from the intestines, and the body responds by secreting water into the intestines. Drugs that reduce constipation this way are called hyperosmotic laxatives. The sugars are also fermented by bacteria in the colon, producing hydrogen gas. (Patients taking the laxatives psyllium or methycellulose  appear to be less likely to pass gas than those taking lactulose.[1]) Both actions expand the colon, which responds by contracting and expelling its contents. Much of the water in the colonic contents is reabsorbed in the colon; the decreased transit time means there is less time for water reabsorption and stools are therefore softer.[2],[3]

In advanced liver disease, ammonia builds up in the body and can enter the brain, causing confusion and even coma, a condition called hepatic encephalopathy. Lactulose slightly acidifies the colon and converts ammonia into ammonium, which is then passed out in the stool.[4] Lactulose is thus an accepted treatment for hepatic encephalopathy.[5]

Hyperosmotic laxatives, such as lactulose, usually take a few days to work. Doses may need adjusting for individual response.[6] Some people dislike the sweet taste.[5],[7] Lactulose is usually taken orally, but it may be administered via enema or nasogastric tube in encephalopathic patients.[5] Laxatives should only be taken for a limited time. If lactulose is used for more than six months or by elderly or debilitated people, electrolytes should be monitored.[8]

When do you really need to take a laxative? You should not take a laxative to “clean out your system” or to make your body act more “normally.” It is untrue that everyone must have a bowel movement daily. Perfectly healthy people may have from three bowel movements per week to three bowel movements per day.

If the frequency of your bowel movements has decreased, if you are having bowel movements less than three times a week, or if you are having difficulty in passing stools, you are constipated, but this does not mean that you need a laxative. It is better to treat simple, occasional constipation without drugs, by eating a high-fiber diet that includes whole-grain breads and cereals, raw vegetables, raw and dried fruits, and beans, and by drinking plenty of nonalcoholic liquids (six to eight glasses per day). This type of diet will both prevent and treat constipation, and it is less costly than taking drugs. Regular exercise—at least 30 minutes per day of swimming, cycling, jogging, or brisk walking—will also help your body maintain regularity.

If you are constipated while traveling or at some other time when it is hard for you to eat properly, it may be appropriate to take a laxative for a short time. The only types of laxatives you should use for self-medication are bulk-forming laxatives such as psyllium or methycellulose or a hyperosmotic laxative such as lactulose. Bulk-forming laxatives usually take effect in 12 hours to three days, compared with docusate (COLACE, SURFAK), which takes effect one or two days after the first dose but may require three to five days of treatment. Even bulk-forming laxatives should only be used occasionally, if possible.

If you are on a special diet such as a low-salt or low-sugar diet, ask your doctor or pharmacist to help you choose a laxative without ingredients you are trying to avoid. Some laxatives contain sugar (up to half of the product), salt (up to 250 milligrams per dose), or the artificial sweetener NutraSweet.

People with diabetes should use lactulose cautiously. Rarely, lactulose causes gas within the bowel wall, a condition called pneumatosis intestinalis that sometimes requires surgery.[9] Infants administered lactulose are especially prone to low blood sodium and dehydration.[4] People who undergo electrocautery procedures during proctoscopy or colonoscopy risk hazard if an electrical spark triggers an explosion with hydrogen gas. Bowel cleansing for these procedures should use a nonfermentable solution.[8]

If diarrhea occurs in the course of treatment for constipation, lactulose should be stopped. Prolonged diarrhea can cause excess sodium in the blood as well as loss of potassium.[5],[10]

Before You Use This Drug [top]

Tell your doctor if you have or have had:

  • abdominal pain
  • allergies to drugs, including to lactose
  • anorexia
  • appendicitis
  • blood in stools
  • colon cancer, including family history
  • diabetes
  • diarrhea
  • galactose-low diet[4]
  • heart problems
  • hypertension (high blood pressure)
  • impaction of stool (intestinal obstruction)
  • inflammatory bowel disease, including family history
  • intestinal obstruction
  • kidney problems
  • nausea or vomiting
  • pregnancy or are breast-feeding
  • weight loss

Tell your doctor about any other drugs you take, including aspirin, herbs, vitamins, and other nonprescription products.

When You Use This Drug [top]

  • Check with your doctor to make certain your fluid intake is adequate and appropriate (e.g., four to six 8-ounce glasses of fluid daily). If you do not get enough fluids, the laxative will not work properly and may dry and harden, clogging the intestine.[4] This is especially true during hot weather or strenuous exercise.
  • Get regular exercise, such as walking
  • Avoid alcohol and medications that may cause constipation.
  • Limit use of candies, gums, and foods containing mannitol or sorbitol, as these may add to effects of lactulose.
  • Do not use other laxatives while on lactulose.[4]
  • Do not use unnecessarily (for a cold, tonic, or clean system).
  • Wait at least two days without a bowel movement before considering use.
  • Check with your doctor if a sudden change lasts more than two weeks.
  • Avoid a laxative habit. Overuse or extended use may cause dependence.
  • Do not use for more than one week. If you have used lactulose for a week, stop taking it to see if a high-fiber diet and liquids alone will work. If your constipation continues for longer than a week, call your doctor.

How to Use This Drug [top]

  • If you use a powder form, open the packet and dissolve contents in water, according to instructions. For liquid forms, measure your dose.
  • Take with a full glass (eight ounces) of water. To improve flavor, mix with fruit juice, citrus-carbonated beverage, or milk. Taking with food or at bedtime may delay results.
  • If you miss a dose, take it as soon as you remember, but skip it if it is almost time for the next dose. Do not take double doses.
  • Do not share your medication with others.
  • Take the drug at the same time(s) each day.
  • Do not use for prolonged periods of time.
  • Store at room temperature with lid on tightly. Do not store in the bathroom. Do not expose to heat, moisture, or strong light. Do not let the liquid form freeze. Keep out of reach of children.

Interactions with Other Drugs [top]

Evaluations of Drug Interactions 2003 lists no drugs, biologics (e.g., vaccines, therapeutic antibodies), or foods as causing “highly clinically significant” or “clinically significant” interactions when used together with the drugs in this section. We also found no interactions in the drugs’ FDA-approved professional package inserts. However, as the number of new drugs approved for marketing increases and as more experience is gained with these drugs over time, new interactions may be discovered.

Adverse Effects [top]

Call your doctor immediately if you experience:

  • abdominal pain
  • confusion
  • diarrhea that is unusual
  • dizziness or lightheadedness
  • heartbeat irregular
  • muscle cramps
  • tiredness or weakness that is unusual

Call your doctor if you continue to experience:

  • appetite decreased
  • bloating
  • bowel habits changed suddenly and continue for two weeks
  • cramping
  • diarrhea
  • gas
  • nausea
  • stomach and/or intestinal cramping
  • thirst

Signs of overdose:

  • abdominal cramp
  • dehydration
  • diarrhea

If you suspect an overdose, call this number to contact your poison control center: (800) 222-1222.

last reviewed March 31, 2021