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Generic name: lactulose (oral) [ LAK-too-lose ]
Brand names: Constulose, Generlac, Kristalose
Drug class: Laxatives

What is Generlac?

Generlac is used to treat chronic constipation.

Generlac is sometimes used to treat or prevent certain conditions of the brain that are caused by liver failure. These conditions can lead to confusion, problems with memory or thinking, behavior changes, tremors, feeling irritable, sleep problems, loss of coordination, and loss of consciousness.

Generlac may also be used for purposes not listed in this medication guide.


Use only as directed. Tell your doctor if you use other medicines or have other medical conditions or allergies.

Before taking this medicine

You should not use Generlac if you are on a special diet low in galactose (milk sugar).

Tell your doctor if you have ever had:

  • diabetes; or

  • if you need to have any type of intestinal test using a scope (such as a colonoscopy).

Tell your doctor if you are pregnant or breastfeeding.

How should I take Generlac?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Mix Generlac powder with at least 4 ounces of water, milk, or fruit juice.

Measure liquid medicine with the supplied measuring device (not a kitchen spoon).

Generlac should produce a bowel movement within 24 to 48 hours.

If you use Generlac long-term, you may need frequent medical tests.

Tell your doctor if you have a planned colonoscopy or proctoscopy procedure.

Store tightly closed at room temperature, away from moisture and heat. Avoid freezing.

The liquid may turn darker in color, but this will not affect the medicine. Do not use the medicine if it becomes very dark or gets thicker or thinner in texture.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose may cause nausea, vomiting, diarrhea, and stomach cramps, or symptoms of low blood potassium or low blood sodium (confusion, weakness, constipation, irregular heartbeats, fluttering in your chest, increased thirst or urination, numbness or tingling, muscle weakness or limp feeling).

What should I avoid while taking Generlac?

Ask your doctor before taking any other laxative or an antacid, and take only the type your doctor recommends.

Generlac side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using Generlac and call your doctor at once if you have severe or ongoing diarrhea.

Common side effects may include:

  • bloating, gas;

  • stomach pain;

  • diarrhea; or

  • nausea, vomiting.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect Generlac?

Other drugs may affect Generlac, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all other medicines you use.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.