Drug Interaction Report

Lactulose and Licorice: Interaction Details

A pharmacist-reviewed analysis of the Lactulose and Licorice interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Lactulose

Cholac® Constilac® Syrup Constulose Constulose® Enulose Enulose® Evalose® Syrup Generlac
+

Licorice

No brand names on record
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
LinkedIn
Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
How we grade severity & evidence

Severity levels

  • Contraindicated: These should generally not be used together.
  • Major: Potentially serious — often needs a change or close monitoring.
  • Moderate: Can be significant — usually manageable with monitoring.
  • Minor: Usually limited clinical impact.

Evidence grades

  • Established: Well documented — supported by controlled studies or strong clinical data.
  • Probable: Good supporting evidence, though not definitively proven.
  • Suspected: Some evidence suggests this interaction, but it is not well established.
  • Possible: Limited or conflicting evidence; the interaction may occur.
  • Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 9 documented Lactulose interactions, 2 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
theoretical
Severity
Major

What happens

Increased risk of hypokalemia

Interaction Deep Dive

Theoretically, concurrent use of licorice and laxatives may lead to additive potassium loss12. Hypokalemic paralysis has resulted from licorice use 3456. Licorice alone has been reported to be the likely cause of hypokalemia, hypertension, and cardiac arrhythmia 789101112. The glycyrrhetinic acid component of licorice is metabolized to 3-monoglucuronyl-glycyrrhetinic acid (3MGA), which inhibits 11-beta-hydroxysteroid dehydrogenase and reduces cortisol breakdown, resulting in a hypermineralocorticoid effect 1314.

Why it happens (mechanism)

Additive potassium loss

Common questions

Can I take Lactulose and Licorice together?

Increased risk of hypokalemia Always confirm with your pharmacist or prescriber before making any change.

How serious is the Lactulose and Licorice interaction?

It is rated major. Potentially serious — often needs a change or close monitoring.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

From our Q&A

Real reader questions about these medications, each personally answered by our pharmacist:

Questions for your pharmacist

  • Does my dose of Lactulose or Licorice need adjusting while I take them together?
  • What symptoms should prompt me to call you or my prescriber right away?
  • Does the timing of my doses matter for this combination?
  • Is there a safer alternative to one of these medications for me?

References (14)

  1. Brinker FBrinker F: Herb Contraindications and Drug Interactions, 2nd. Eclectic Medical Publications, Sandy, OR, 1998.
  2. McGuffin M, Hobbs C, Upton R, et alMcGuffin M, Hobbs C, Upton R, et al (Eds): American Herbal Products Association's Botanical Safety Handbook, CRC Press, Boca Raton, FL, 1997.
  3. Hussain RM: The sweet cake that reaches parts other cakes can't!. Postgrad Med J 2003; 79:115-116. PubMed
  4. Lin SH, Yang SS, Chau T, et al: An unusual cause of hypokalemic paralysis: chronic licorice ingestion. Am J Med Sci 2003; 325(3):153-156. DOI
  5. Shintani S, Murase H, Tsukagoshi H, et al: Glycyrrhizin (Licorice)-induced hypokalemic myopathy. Eur Neurol 1992; 32(1):44-51. DOI
  6. Corsi FM, Galgani S, Gasparini C, et al: Acute hypokalemic myopathy due to chronic licorice ingestion: report of a case. Ital J Neurol Sci 1983; 4(4):493-497. DOI
  7. Dellow EL, Unwin RJ, & Honour JW: Pontefract cakes can be bad for you: refractory hypertension and liquorice excess. Nephrol Dial Transplant 1999; 14:218-220. PubMed
  8. Eriksson JW, Carlberg B, & Hillorn V: Life-threatening ventricular tachycardia due to liquorice-induced. J Int Med 1999; 245(3):307-310.
  9. Kageyama K, Watanobe H, Nishie M, et al: A case of pseudoaldosteronism induced by a mouth refresher containing licorice. Endocr J 1997; 44(4):631-632. PubMed
  10. Bernardi M, D'Intino PE, Trevisani F, et al: Effects of prolonged ingestion of graded doses of licorice by healthy volunteers. Life Sci 1994; 55(11):863-872. PubMed
  11. Blachley JD & Knochel JP: Tobacco chewer's hypokalemia: licorice revisited. N Engl J Med 1980; 302(14):784-785. DOI
  12. Wash LK & Bernard JD: Licorice-induced pseudoaldosteronism. Am J Hosp Pharm 1975; 32(1):73-74. DOI
  13. Kato H, Kanaoka M, Yano S, et al: 3-Monoglucuronyl-glycyrrhetinic acid is a major metabolite that causes licorice-induced pseudoaldosteronism. J Clin Endocrinol Metab 1995; 80(6):1929-1933. PubMed
  14. Walker BR & Edwards CRW: Licorice-induced hypertension and syndromes of apparent mineralocorticoid excess. Endocrinol Metab Clin North Am 1994; 23:359-377. DOI
Was this write-up helpful?
Lactulose

Keep reading about Lactulose

All Lactulose interactions (9) Lactulose drug information
Also serious with: Levomethadyl
Licorice

Keep reading about Licorice

All Licorice interactions (38)
Also serious with: Bisacodyl Bisacodyl Rectal Castor Oil Linezolid Injection
Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Lactulose + Activated Charcoal Coffee Charcoal European Mandrake Glucomannan Guar Gum Gum Arabic Slippery Elm Tragacanth + 9 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

Check another combination

Our instant two-drug interaction checker is almost here.

Coming soon

The instant two-drug checker is on its way.

In the meantime, browse the directory below to look up any drug and see its documented interactions.

Still have questions about this combination?

Every question gets a real answer from a licensed pharmacist — free, and usually within a day.

Ask the pharmacist
This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.