Lactulose and Lithium Carbonate: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Lactulose
Lithium Carbonate
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.
What happens
Increased lithium concentrations and lithium toxicity
Interaction Deep Dive
Use caution when prescribing lactulose to patients who take lithium. Concomitant use of lithium and lactulose may cause elevated lithium plasma concentrations. Serum lithium levels greater than 1.5 mEq/L were reported in 3 patients who were taking lithium and lactulose concomitantly. If using both drugs together, monitor for increased lithium side effects and maintain adequate hydration1.
Why it happens (mechanism)
Volume depletion increase and renal tubular reabsorption of lithium
Literature reports
1 report — tap to read
a) Serum lithium levels were greater than 1.5 mEq/L in 3 patients who were taking lithium and lactulose concomitantly. In the first case, a 47-year-old male had a lithium level of 1.6 mEq/L with a serum creatinine level of 0.57 mg/dL after taking two doses of lactulose 30 mg along with lithium 300 mg twice daily. No adverse outcomes were reported and a later lithium level was 1.2 mEq/L. The probability of adverse drug reaction was 6 on the Naranjo scale. The second case was a 45-year-old woman who began taking 450 mg lithium in the morning and 600 mg at night along with 30 mL of lactulose for 3 days. Nine days later her lithium level reached 2.4 mEq/L. She reported mild fatigue, but no other signs of lithium toxicity. After discontinuation and observation in a hospital, her lithium levels normalized. This case scored a 3 on the Naranjo scale; it is notable that she was also taking hydrochlorothiazide and lisinopril. The third case involved a 48-year-old woman who was increased to lithium 900 mg twice daily and received 5 doses of lactulose 30 mg over 2 days. She reported drowsiness and tremor and her lithium level reached 1.6 mEq/L. After reducing her lithium dose to 300 mg in the morning and 600 mg in the evening, her lithium level normalized. The Naranjo score on this case was 4; notably, she was also taking benazepril 1
Common questions
Can I take Lactulose and Lithium Carbonate together?
Increased lithium concentrations and lithium toxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Lactulose and Lithium Carbonate interaction?
It is rated moderate. Can be significant — usually manageable with 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 "probable". Good supporting evidence, though not definitively proven.
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 Lithium Carbonate 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 anything you'd monitor while I'm on both?
References (1)
- Bregman A, Fritz K, & Xiong GL: Lactulose-associated lithium toxicity: a case series. J Clin Psychopharmacol 2014; 34(6):742-743. PubMed
Keep reading about Lactulose
Keep reading about Lithium Carbonate
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:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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