Lactulose and Lactose Intolerance: Is It Safe?
Digestive HealthLactose Intolerance

Lactulose and Lactose Intolerance

Lactulose and Lactose Intolerance
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Updated on August 7, 2025
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Lactulose is a man-made sugar that’s commonly used as a stool softener to treat constipation.

 It can also treat certain complications from liver disease.
Lactulose is made from lactose.

 But people with lactose intolerance can generally take the medication due to its chemical composition, unless they are sensitive to trace elements of lactose in the medication.
This medication can cause cramping, diarrhea, bloating, and stomach pain that aren’t related to lactose intolerance.

Talk with your doctor before taking lactulose, regardless of whether you are lactose intolerant.

What Is Lactulose?

Lactulose is a synthetic sugar made from lactose.

The medication treats constipation by drawing water to stool in the colon. This causes the stool to pass with greater ease.

Lactulose also treats complications from liver disease by pulling ammonia from your blood to your colon for excretion. This can prevent or treat hepatic encephalopathy, a brain condition that happens when your liver can’t properly filter toxins like ammonia from your blood.

This medication is available as a syrup that can be taken two to four times daily for constipation, or up to four times daily for liver disease (with doctor supervision).

What Is Lactose Intolerance?

Lactose intolerance is a condition that causes trouble digesting lactose, a sugar that is mainly found in milk.

Most sugars that you ingest need an enzyme to break them down into simple sugars.

Lactase is the enzyme required to digest lactose properly.

 If you don’t make enough lactase in your small intestine, your body will not be able to absorb the sugar and it will pass through your gut undigested.
The undigested lactose creates gas, cramping, diarrhea, and bloating once it reaches the colon.

Can I Have Lactulose If I’m Lactose Intolerant?

Due to its chemical composition, lactulose passes straight through your small intestine, and it can only be broken down by bacterial fermentation.

 This means, unlike in lactose digestion, you do not need sufficient lactase to digest the medication.
But lactulose can contain trace amounts of lactose due to an incomplete chemical rearrangement of lactose during manufacturing.

These trace amounts are typically monitored. For example, the European Pharmacopoeia set “acceptable limits” of lactose and other sugars in lactulose crystals.

 The U.S. Pharmacopeia also monitors trace sugar in lactulose.

The amounts are typically quite low, but it’s possible that you could still get symptoms of lactose intolerance as a result.

Lactulose and Digestive Discomfort

Side effects of lactulose include many typical symptoms of lactose intolerance. These include diarrhea, gas, nausea, and stomach cramping.

While these symptoms are common with the medication, they can become worse if you are lactose intolerant.

If you develop serious symptoms after taking this medication, stop using it and call your doctor for advice.

EDITORIAL SOURCES
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Resources
  1. Lactulose. MedlinePlus. January 15 2024.
  2. Lactulose. Cleveland Clinic.
  3. Mukherjee S et al. Lactulose. StatPearls. February 8, 2024.
  4. Hepatic Encephalopathy. Cleveland Clinic. December 19, 2023.
  5. Chandel NS. Carbohydrate Metabolism. Cold Spring Harbor Perspectives in Biology. January 2021.
  6. Lactose Intolerance. Cleveland Clinic. March 3, 2023.
  7. Lactose Intolerance: Learn More – Causes and Diagnosis of Lactose Intolerance. Informedhealth.org. November 20, 2024.
  8. Steudle J et al. Blood Glucose Response After Oral Intake of Lactulose in Healthy Volunteers: A Randomized, Controlled, Cross-Over Study. World Journal of Gastrointestinal Pharmacology and Therapeutics. August 7, 2018.
  9. USP Reference Standards. U.S. Pharmacopeia (USP).
  10. Lactulose: Uses & Side Effects. Cleveland Clinic.
Additional Sources

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    Yuying Luo, MD

    Medical Reviewer

    Yuying Luo, MD, is an assistant professor of medicine at Mount Sinai West and Morningside in New York City. She aims to deliver evidence-based, patient-centered, and holistic care for her patients.

    Her clinical and research focus includes patients with disorders of gut-brain interaction such as irritable bowel syndrome and functional dyspepsia; patients with lower gastrointestinal motility (constipation) disorders and defecatory and anorectal disorders (such as dyssynergic defecation); and women’s gastrointestinal health.

    She graduated from Harvard with a bachelor's degree in molecular and cellular biology and received her MD from the NYU Grossman School of Medicine. She completed her residency in internal medicine at the Icahn School of Medicine at Mount Sinai, where she was also chief resident. She completed her gastroenterology fellowship at Mount Sinai Hospital and was also chief fellow.

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    Diane Marks is a healthcare writer and administrator focusing on practical health guidance.

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