Lactulose, Constulose, Kristalose

Introduction

Written by Ashley Wong, PharmD
Medically reviewed by Victor Nguyen, PharmD, MBA
Updated on October 12, 2023

Lactulose (LAK tyoo lose) is a generic medication prescribed for constipation. Doctors also prescribe it for a brain disorder caused by liver disease. Lactulose belongs to a group of drugs called laxatives. 

These approved uses differ based on the form of lactulose your doctor prescribes.

This article doesn’t provide coupons for all forms of lactulose. To find coupons for lactulose oral/rectal solution, see this article. 

Side effects of lactulose

Lactulose may cause mild or serious side effects. This section summarizes the more common mild side effects of lactulose and its serious side effects. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about lactulose’s side effects, ask your doctor or pharmacist. You can also refer to the prescribing information for lactulose listed in the “Resources” section.

Mild side effects

The list below includes more common mild side effects reported with some forms of lactulose. This article doesn’t include all possible mild side effects of the drug. To learn more about lactulose’s side effects based on the form, refer to the prescribing information for lactulose listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Lactulose oral solution’s mild side effects include:

• gas
• stomach cramps
• nausea
• vomiting
• mild allergic reaction*

Lactulose oral/rectal solution’s mild side effects include:

• gas
• burping (belching)
• stomach discomfort or cramping
• nausea
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for lactulose” section.

Serious side effects

The list below includes serious side effects of lactulose. These side effects may differ based on the form of lactulose you use. 

This article doesn’t include all possible serious side effects of the drug. To learn more about lactulose’s side effects based on the form, refer to the prescribing information for lactulose listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number. 

In general, lactulose’s serious side effects include:

• severe diarrhea
• dehydration
• low potassium levels
• high sodium levels
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for lactulose“ section.

Uses of lactulose

The Food and Drug Administration (FDA) approves prescription drugs such as lactulose for certain conditions. Approved uses for lactulose are described below. These uses differ based on the form of lactulose prescribed.

Use for brain disorder caused by liver disease

Doctors may prescribe lactulose oral/rectal solution for treating and preventing portal-systemic encephalopathy. This is a brain disorder that’s also known as hepatic encephalopathy. Doctors may prescribe it for adults and some children. They may prescribe it as a long-term or short-term treatment.

A healthcare professional may administer the oral/rectal solution, depending on the severity of the condition.

With portal-systemic encephalopathy, your liver has difficulty removing toxins from your blood, including ammonia. This causes toxins to build up in your bloodstream. These toxins can travel to your brain and affect your brain function. This can cause symptoms such as confusion, forgetfulness, and difficulty thinking.

To treat or prevent portal-systemic encephalopathy, lactulose works by lowering ammonia levels in your blood.

Use for constipation

Doctors may prescribe lactulose oral solution for treating constipation. Doctors may prescribe it for adults. They may prescribe it as a short-term treatment.

With constipation, you may have hard, dry stools. Or you may have fewer than three bowel movements per week. You might also strain during bowel movements or feel pain.

Lactulose treats constipation by pulling more water into your stools to soften them. This makes them easier to pass. 

Interactions and warnings for lactulose

Below you’ll find information about lactulose’s possible interactions and warnings. 

Interactions of lactulose

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or using the drug along with other medications. This effect is called a drug interaction. 

Before you use lactulose, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for lactulose” section below.

Warnings for lactulose

Lactulose could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether lactulose is a safe option for you. These warnings may differ based on the form of lactulose you use.

Ask your doctor about specific warnings for lactulose, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Lactulose can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to lactulose or any of its ingredients, your doctor likely will not prescribe lactulose. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems 

If you have an allergic reaction to lactulose, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of lactulose

You should not use more lactulose than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve used too much lactulose, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have symptoms that concern you, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and lactulose

Information about lactulose and pregnancy and breastfeeding is described below.

Lactulose and pregnancy

In general, lactulose is considered safe to use during pregnancy. That said, ask your doctor whether they feel it’s safe for you. 

Lactulose and breastfeeding

It’s not known whether lactulose should be used while breastfeeding. If you’re breastfeeding or planning to do so, talk with your doctor before using this medication. 

Common questions about lactulose

Below you’ll find answers to a few commonly asked questions about lactulose.

Is lactulose similar to Miralax?

Yes, the drugs are similar in some ways. Lactulose and Miralax both are approved to treat constipation. Both also belong to the same group of drugs called laxatives. 

While lactulose is available only by prescription from your doctor, Miralax is available over the counter without a prescription. 

If you have questions about what’s the best treatment for you, talk with your doctor. 

How does lactulose work? And how long does it take to start working?

Lactulose oral/rectal solution treats and helps prevent portal-systemic encephalopathy. This is a brain disorder that’s also called hepatic encephalopathy. It works by drawing ammonia from the blood into the colon. Ammonia then exits your body through your stool. Lactulose oral/rectal solution can start working within 24 hours. But in some cases, it can take 48 hours or more.

Lactulose oral solution treats constipation. It works by drawing water into your stools. This softens your stools and makes them easier to pass. With this solution, it can take about 24–48 hours for you to have a bowel movement. 

To learn more about either form of lactulose, talk with your doctor or pharmacist. 

What to ask your doctor

Let your doctor know if you have questions about lactulose or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• Are there any drug interactions I should avoid when I’m using lactulose?
• What are the possible side effects if you prescribe lactulose long term?
• How will I know if lactulose is working?

Resources

• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Lactulose solution USP, 10 g/mL. (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/cbf0497c-9c8d-4dfa-bebd-64c589468401/spl-doc
• Lactulose solution USP, 10 g/15 mL. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/e75c335b-f19e-42e2-a24f-d891a52d3d34/spl-doc

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.