What Is Constulose Used For? Understanding the Drug’s Dual Purpose

October 6, 2025 •

4 min read

Constulose, a brand name for the prescription drug lactulose, is primarily known for its dual purpose: acting as a gentle yet effective laxative and managing a serious liver condition. It is important to note that while the Constulose brand has been discontinued, the generic formulation, lactulose, remains widely available for these purposes.

Quick Summary

Constulose, the brand name for lactulose, is a prescription medication used to treat chronic constipation by drawing water into the colon. It also manages hepatic encephalopathy by reducing blood ammonia levels via colonic acidification.

Key Points

Dual Functionality: Constulose, the brand name for lactulose, is a prescription drug used for treating chronic constipation and managing hepatic encephalopathy.
Laxative Action: For constipation, it works as an osmotic laxative, drawing water into the colon to soften stool and ease bowel movements.
Hepatic Encephalopathy Management: In liver disease, it lowers the colon's pH, which converts toxic ammonia ($NH_3$) into non-absorbable ammonium ions ($NH_4^+$) for elimination.
Prescription Only: Constulose is a prescription-only medication, and while the brand is discontinued in the US, the generic lactulose is widely available.
Delayed Effect: It can take 24 to 48 hours for Constulose to produce a bowel movement.
Common Side Effects: Patients may experience gas, bloating, and stomach cramps, especially at the start of treatment.
Electrolyte Risk: Excessive doses that cause severe diarrhea can lead to fluid and electrolyte imbalances.
Important Precautions: The medication is contraindicated in individuals with galactosemia and requires caution in diabetic patients.

What is Constulose?

Constulose is the brand name for the generic prescription drug lactulose. It is a synthetic sugar solution that is not easily absorbed by the body. While the Constulose brand name has been discontinued in the United States, generic versions of lactulose remain a staple in medical practice. Its efficacy stems from its unique mechanism of action, which makes it suitable for treating two distinct medical conditions: chronic constipation and hepatic encephalopathy.

The Dual Mechanism of Action

The way lactulose works is dependent on the condition it is treating, though both actions occur within the colon. After oral administration, lactulose largely bypasses digestion in the small intestine and reaches the colon unchanged. In the colon, it is metabolized by intestinal bacteria into low-molecular-weight organic acids. This is the key to both its functions.

How Constulose Treats Chronic Constipation

For individuals with chronic constipation, lactulose functions as an osmotic laxative. The organic acids produced from lactulose metabolism increase the water content in the stool, softening it and making it easier to pass. This osmotic effect also increases intestinal pressure, which prompts the bowel muscles to move stool along. Patients should be aware that it can take 24 to 48 hours to produce a normal bowel movement after taking a dose. To aid its efficacy, patients are often advised to increase their fluid intake.

How Constulose Manages Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a neurological complication of severe liver disease where the liver can no longer effectively filter toxins, such as ammonia ($NH_3$), from the blood. For HE, lactulose's primary role is to reduce the amount of toxins absorbed from the large intestine. It achieves this through several key processes in the colon:

Acidification: The bacterial breakdown of lactulose to lactic, acetic, and formic acids acidifies the colon's contents.
Ammonia Trapping: This acidic environment favors the conversion of ammonia ($NH_3$) into non-absorbable ammonium ions ($NH_4^+$). This traps the ammonia in the colon, preventing it from being reabsorbed into the bloodstream.
Increased Excretion: The osmotic laxative effect of lactulose then expedites the expulsion of these trapped ammonium ions through frequent bowel movements.

The goal for HE treatment is typically to cause two to three soft bowel movements per day, with the dosage adjusted to achieve this specific response.

Comparison with Other Laxatives

Different types of laxatives work in different ways and are used for various purposes. Here is a comparison of Constulose (lactulose) with two common alternatives, based on their mechanisms of action and common uses.


Feature	Constulose (Lactulose)	Polyethylene Glycol (PEG) (Miralax)	Stimulant Laxatives (e.g., Bisacodyl)
Mechanism	Osmotic, non-absorbable sugar broken down by bacteria in the colon, drawing water into the stool. Also acts as a colonic acidifier for HE.	Osmotic, inert compound that holds water in the stool.	Stimulates the intestinal muscles to contract, speeding up bowel movements.
Onset of Action	24 to 48 hours for constipation relief.	12 to 72 hours for constipation relief.	6 to 12 hours orally; faster rectally.
Primary Uses	Chronic constipation; prevention and treatment of hepatic encephalopathy.	Occasional and chronic constipation.	Short-term relief of occasional constipation, bowel preparation.
Common Side Effects	Gas, bloating, abdominal cramps, diarrhea (with high doses).	Bloating, gas, nausea, stomach cramps.
Specific Considerations	Can cause electrolyte imbalances with excessive use, especially in the elderly. Requires caution in diabetics.	Generally well-tolerated with minimal side effects.
Long-Term Use	Can be used long-term under medical supervision for HE.	Considered safe for occasional long-term use with medical advice.	Not recommended for long-term use due to potential dependence.

Potential Side Effects and Precautions

While generally safe, Constulose (lactulose) can cause side effects. Awareness and proper management are key.

Common side effects include:

Flatulence (gas)
Bloating
Abdominal cramps
Belching
Nausea and vomiting

More serious side effects, often due to excessive dosing leading to severe diarrhea, can cause fluid and electrolyte imbalances. These include:

Hypokalemia (low potassium)
Hypernatremia (high sodium)
Dehydration
Severe abdominal pain

Certain individuals should use Constulose with caution or avoid it entirely:

Galactosemia: A rare inherited disorder where the body cannot process galactose. Since lactulose contains small amounts of galactose, it is contraindicated.
Diabetes: It contains sugars, so blood sugar levels should be monitored, especially in diabetic patients, though significant elevation is uncommon.
Intestinal Obstruction: Should not be used in cases of known or suspected intestinal obstruction.
Inflammatory Bowel Disease (IBD): Use with caution.

How to Take Constulose

Constulose, available as a liquid solution or powder packets (generic lactulose), is taken orally. The dosage and frequency are determined by a healthcare provider based on the condition and individual response.

Oral Solution: The liquid form can be mixed with fruit juice, water, or milk to improve its sweet taste.
Powder Packets: The powder should be dissolved in a half-glass of water.
Consistency is key: For maximum benefit, it should be taken regularly as prescribed, often at the same time each day.
Hydration: Drink plenty of water throughout the day to prevent dehydration, particularly with higher doses.

Conclusion

Constulose (lactulose) is a valuable prescription medication with two distinct applications: relieving chronic constipation and managing hepatic encephalopathy. Its effectiveness lies in its unique ability to draw water into the colon for laxation and to lower the colonic pH to trap and expel ammonia. Due to the brand name Constulose being discontinued, patients will likely be prescribed the generic lactulose instead. Proper usage requires following a doctor’s instructions, monitoring for side effects like gas and diarrhea, and being aware of contraindications like galactosemia. Given its potency and specific applications, lactulose should always be used under the supervision of a healthcare professional. For more in-depth information, resources like the MedlinePlus drug information page on lactulose offer comprehensive details.

Frequently Asked Questions

Constulose, or its generic form lactulose, is primarily used to treat chronic constipation and to manage or prevent the neurological symptoms of hepatic encephalopathy in people with liver disease.

For constipation, it can take anywhere from 24 to 48 hours after taking a dose before you have a normal bowel movement.

Common side effects include temporary gas, bloating, intestinal cramps, nausea, and vomiting. If the dosage is too high, it can lead to diarrhea.

Yes, but with caution. Constulose contains sugars (lactose and galactose), so diabetic patients should monitor their blood sugar levels regularly as directed by their doctor, though it's not known to cause significant blood sugar spikes.

It helps by drawing ammonia from the blood into the colon, where it is trapped by an acidic environment created by the medication. The ammonia is then expelled from the body via bowel movements.

The brand name Constulose has been discontinued in the U.S., but the generic form, lactulose, is widely available by prescription.

To improve the taste of the oral solution, you can mix it with fruit juice, water, or milk.

Taking too much can cause diarrhea and abdominal cramps. Severe or persistent diarrhea may lead to dehydration and electrolyte imbalances, so you should contact your doctor if this occurs.