4 Kristalose (Lactulose) Side Effects and How to Manage Them

Kristalose (lactulose) is an osmotic laxative that’s used to treat chronic constipation. It increases the frequency of bowel movements by drawing fluid into the colon to soften stool and help it pass more easily. The medication comes in powder packets. You dissolve one packet into a half glass (4 oz) of water and then drink the solution to take a dose.

Your gut doesn’t absorb Kristalose, which allows it to reach your colon intact and do its job. The downside is that this can result in unpleasant side effects, like gas, bloating, and cramps. But these side effects tend to be short-lived.

Below, we cover what you should know about four Kristalose side effects and what to do if they happen to you.

1. Gas and bloating

You may experience gas and bloating when first starting treatment with Kristalose. Fortunately, these side effects usually go away relatively quickly on their own. But if needed, an over-the-counter (OTC) medication like Gas-X (simethicone) can help provide relief.

Speak with your healthcare provider if you have gas or bloating that becomes bothersome or painful. And, again, keep in mind that these effects may occur initially, but they should resolve quickly. 

2. Cramps

Along with gas, intestinal cramps are a Kristalose side effect that you may experience with your first few doses. Cramps can be a sign that the medication is starting to work and that your stool is moving through your gastrointestinal (GI) tract. While they can be unpleasant, the cramps should go away without any treatment.

But if your cramps don’t improve, or get worse, contact your healthcare provider. And if they’re accompanied by fever, unexpected bleeding, or uncontrollable vomiting, go to the nearest emergency room.

3. Diarrhea

Since Kristalose is used to treat constipation, it can lead to diarrhea — especially with higher doses. But before you turn to an OTC diarrhea medication, talk to your healthcare provider. This type of medication could worsen constipation that may have led you to take Kristalose in the first place. 

However, you should drink plenty of fluids to prevent dehydration. In addition to dehydration, severe, untreated diarrhea can cause low blood potassium levels (hypokalemia) and high blood sodium levels (hypernatremia). So contact your healthcare provider if you have persistent or severe diarrhea while taking Kristalose.

4. Nausea and vomiting

Some people taking Kristalose have reported experiencing nausea and vomiting as side effects. You can take Kristalose with or without food. But, if it’s making you feel queasy, try taking it with a small meal or snack. If that doesn’t help, or if you start vomiting after taking a dose, speak with your healthcare provider.

When should you contact your healthcare provider about Kristalose side effects?

The most common Kristalose side effects are usually mild and go away on their own without treatment. But if you experience side effects that get worse or don’t go away, speak with your healthcare provider.

While less common, Kristalose does have some potential serious side effects. Symptoms like severe diarrhea and vomiting should be reported to your healthcare provider right away. Early treatment can prevent more serious complications, such as dehydration and electrolyte problems.

If your symptoms feel severe or life-threatening, consider going to the nearest emergency room.

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Written by:

Brian Leonard, PharmD, BCACP, BCGP

Brian Leonard earned his doctorate in pharmacy from the University of Florida College of Pharmacy and is board certified in Ambulatory Care and Geriatric Pharmacy.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

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