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Lactulose is used to treat constipation and to prevent and treat a brain condition that can happen in people with liver disease (hepatic encephalopathy). It relieves constipation by drawing water into the colon, making the stool (poop) softer and easier to pass. It prevents and treats hepatic encephalopathy by helping the body get rid of ammonia. Common side effects include bloating, gas, burping, and stomach discomfort. Lactulose is available as a liquid that is swallowed or given rectally.

Uses

What is lactulose used for?

Lactulose is commonly used for the following conditions.

  • To treat constipation
  • To prevent and treat hepatic encephalopathy, a brain condition that sometimes occurs in people with liver disease. In this condition, toxins (such as ammonia) build up and cause symptoms like confusion, memory problems, and personality changes.

Lactulose may also be used for other conditions as determined by your healthcare provider.

How does lactulose work (mechanism of action)?

For constipation, lactulose works by drawing water into the colon, making the stool (poop) softer and easier to pass. Lactulose usually starts working within 24 to 48 hours.

For hepatic encephalopathy (HE), lactulose works in the colon by making it more acidic. This triggers a chemical reaction that, along with its laxative effect, helps the body get rid of ammonia and reduces the severity of HE.  

How is lactulose supplied (dosage forms)?

Brands and other names

  • Cephulac
  • Chronulac
  • Constulose
  • Enulose
  • Generlac
  • Kristalose

Dosage forms and strengths

  • 10 g/15 mL oral solution
  • 10 g/15 mL solution for oral or rectal administration
  • 10 g packets of powder for oral solution
  • 20 g packet of powder for oral solution

How should I store lactulose?

Oral or Rectal Liquid. Lactulose oral or rectal liquid should be stored at room temperature, between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place and protect from direct light. Do not freeze. Keep tightly closed. 

When stored properly, the liquid may become darker. This is normal and you can still use the medicine. If the liquid becomes very dark and cloudy, do not use it. Ask your pharmacist if you are unsure how to store or use your lactulose product. 

Oral Powder. Lactulose powder should be stored at room temperature, between 59 F to 86 F (15 C to 30 C). Store in a cool, dry place. 

Side Effects

What are the most common side effects of lactulose?

The most common side effects of lactulose are listed below. Tell your healthcare provider if you have any of these side effects that bother you.

  • Bloating
  • Gas 
  • Burping
  • Stomach discomfort or cramps

There may be other side effects of lactulose that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of lactulose?

While less common, the most serious side effects of lactulose are described below, along with what to do if they happen.

Severe Allergic Reactions. Lactulose may cause allergic reactions, which can be serious. Stop using lactulose and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Warnings & Precautions

Who should not use lactulose?

Allergies to Ingredients. People who are allergic to any of the following should not use lactulose.

  • Lactulose
  • Cephulac
  • Chronulac
  • Constulose
  • Enulose
  • Generlac
  • Kristalose
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific lactulose products they stock.

Low-Galactose Diet. People with a condition called galactosemia cannot process certain types of sugar, such as lactose and galactose. These people may need to follow a special diet, called a low-galactose diet. Lactulose should not be used if you follow a low-galactose diet. 

What should I know about lactulose before using it?

Do not use lactulose unless it has been prescribed to you by a healthcare provider. Use it as prescribed.

Do not share lactulose with other people, even if they have the same condition as you. It may harm them.

Keep lactulose out of the reach of children. Some lactulose products do not have child-resistant packaging.

Some lactulose products must be dissolved in water before use. Make sure that you or a caregiver understands how to properly prepare and use your lactulose product. If you have any questions, talk to your healthcare provider.

Some forms of lactulose solution can be mixed with fruit juice, water, or milk. Ask your healthcare provider or pharmacist if you have any questions. 

When using lactulose, tell your healthcare provider if you have diarrhea. Diarrhea may lead to dehydration or other problems. Your dose of lactulose may need to be adjusted if you have diarrhea. 

Keep all follow-up appointments with your healthcare provider and for bloodwork. 

What should I tell my healthcare provider before using lactulose?

Tell your healthcare provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if lactulose is right for you.

In particular, make sure that you discuss any of the following.

Diabetes. Tell your healthcare provider if you have diabetes or high blood sugar. 

Medical Procedures. Tell your healthcare provider if you are having a procedure such as a proctoscopy or colonoscopy.

Other Medicines and Supplements. Lactulose may interact with other medicines and supplements. Before using lactulose, tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how lactulose could affect pregnancy or harm an unborn baby. Tell your healthcare provider if you are or plan to become pregnant. 

Breastfeeding. It is not known if lactulose passes into breast milk. Tell your healthcare provider if you are breastfeeding or plan to breastfeed. Your healthcare provider will advise you if you should use lactulose while breastfeeding.

Interactions

Does lactulose interact with foods or drinks?

There are no known interactions between lactulose and foods or drinks.

It is unknown if drinking alcohol will affect lactulose.

Does lactulose interact with other medicines (drug interactions)?

Always tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. 

In particular, make sure that you discuss if you are using any of the following before using lactulose.

  • An antacid, which is a medicine used to relieve heartburn or indigestion
  • Neomycin or any other antibiotic, which is a medicine used for bacterial infections
  • Any other laxative 

This may not be a complete list of medicines that can interact with lactulose. Always check with your healthcare provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much lactulose?

If you or someone else has used too much lactulose, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of lactulose?

If you miss a dose, use it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only use the next dose. Do not use double or extra doses.