Metformin and Rifampin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Rifampin
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 plasma concentrations; enhanced glucose lowering effects of metformin
Interaction Deep Dive
Use caution when prescribing rifampin to patients who are taking metformin. In a pharmacokinetic study (n=16) with healthy volunteers, concurrent administration of rifampin increased metformin plasma concentrations and enhanced the glucose lowering effects of metformin1. Consider monitoring patients for increased metformin adverse effects whenever rifampin is added to metformin therapy. Closely monitor blood glucose levels and for signs and symptoms of hypoglycemia in patients taking metformin and rifampin concurrently.
Why it happens (mechanism)
Increased organic cation transporter (OCT1) expression and hepatic uptake of metformin
Literature reports
1 report — tap to read
a) In a pharmacokinetic study (n=16) in healthy volunteers, concurrent administration of rifampin increased metformin plasma concentrations and enhanced the glucose lowering effects of metformin. Participants received 2 doses of metformin (1750 mg total) on days 1 and 2, and again on days 13 and 14 after a 10-day course of rifampin. Oral glucose tolerance testing was performed before and after each dose of metformin to assess glucose-lowering effects. The difference in maximum glucose level before and after metformin treatment was increased by 41.9% with rifampin treatment (31 +/- 14 mg/dL or 1.72 +/- 0.77 mmol/L vs 44 +/- 14 mg/dL or 2.44 +/- 0.77 mmol/L), respectively; p=0.024). Also, the difference in partial area under the plasma concentration-time curve for glucose (0 to 60 minutes after ingestion) before and after metformin treatment was increased by 54.5% with rifampin treatment (914 +/- 510 mg/dL x min vs 1412 +/- 555 mg/dL x min, respectively; p=0.02). Rifampin increased metformin plasma concentrations by 23% (p=0.002) and 13% (p=0.036) at 0.5 and 1 hour, respectively. Rifampin significantly increased the clearance of metformin by 16% (p=0.008) while the elimination half-life of metformin was not significantly changed. Rifampin treatment increased organic cation transporter (OCT1) mRNA levels by approximately 4.1-fold; however, no OCT2 mRNA was detected in the peripheral blood cells 1.
Common questions
Can I take Metformin and Rifampin together?
Increased metformin plasma concentrations; enhanced glucose lowering effects of metformin Always confirm with your pharmacist or prescriber before making any change.
How serious is the Metformin and Rifampin interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How strong is the evidence for this interaction?
The evidence is graded "established". Well documented — supported by controlled studies or strong clinical data.
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 Rifampin 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)
- Cho SK, Yoon JS, Lee MG, et al: Rifampin enhances the glucose-lowering effect of metformin and increases OCT1 mRNA levels in healthy participants. Clin Pharmacol Ther 2011; 89(3):416-421. PubMed
Keep reading about Rifampin
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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