Metformin and Cimetidine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Cimetidine
Metformin
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 metFORMIN exposure and an increased risk of lactic acidosis
Interaction Deep Dive
Concomitant use of drugs that interfere with common renal tubular transport systems involved in the renal elimination of metFORMIN (eg., multidrug and toxin extrusion [MATE] inhibitors such as cimetidine) could increase systemic exposure to metFORMIN and may increase the risk of lactic acidosis. Coadministration of metFORMIN 850 mg with cimetidine 400 mg may increase the exposure of metFORMIN. The geometric mean ration of metFORMIN with or without cimetidine was 1.4 and 1.61 for AUC (0 to infinity) and Cmax respectively. The benefits and risks of concomitant use should be considered12.
Why it happens (mechanism)
Inhibition of MATE1/2-mediated renal elimination of metFORMIN; inhibition of OCT2-mediated renal elimination of metFORMIN
Literature reports
1 report — tap to read
Common questions
Can I take Metformin and Cimetidine together?
Increased metFORMIN exposure and an increased risk of lactic acidosis Always confirm with your pharmacist or prescriber before making any change.
How serious is the Metformin and Cimetidine 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 "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 Metformin or Cimetidine 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 (2)
- Product Information: KAZANO oral tablets, alogliptin, metformin hydrochloride oral tablets. Takeda Pharmaceuticals America Inc (per FDA), Lexington, MA, 2023. DailyMed
- Product Information: ACTOPLUS MET oral tablets, pioglitazone metformin hydrochloride oral tablets. Takeda Pharmaceuticals America, Inc. (per FDA), Lexington, MA, 2024. DailyMed
Keep reading about Cimetidine
Keep reading about Metformin
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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