Goldenseal and Metformin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Metformin
Goldenseal
No brand names on record
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
Decreased metformin exposure
Interaction Deep Dive
Concomitant use of goldenseal and metformin decreases metformin exposure, which may impair glucose control. Use of a supplement containing goldenseal is not recommended in patients receiving metformin for treatment of type 2 diabetes mellitus1.
Why it happens (mechanism)
Inhibition of luminal uptake of metformin
Literature reports
1 report — tap to read
a) In an open-label, fixed sequence crossover study including 16 healthy volunteers (8 men and 8 women), coadministration of goldenseal and metformin significantly decreased metformin AUC(0 to infinity) by 23% (geometric mean ratio [GMR], 0.77; 95% CI, 0.71 to 0.83) and Cmax by 27% (GMR, 0.73; 95% CI, 0.66 to 0.81); metformin clearance and half life were not significantly altered. At baseline (Arm 1), participants were administered an oral transporter probe cocktail containing furosemide 1 mg, metformin 50 mg, rosuvastatin 10 mg, and midazolam 2.5 mg. During Arm 2, participants were administered 1 g goldenseal three times daily at 4-hour intervals (approximately 8 am, 12 pm, and 4 pm) for 5 consecutive days. The oral probe cocktail was administered on day 6 in the morning with 1 g goldenseal, followed by 2 additional doses of goldenseal 1 g in 4-hour intervals. Patients were a median of 26 to 27 years (range, 23 to 42 years) and none were receiving concomitant medications or natural products known to affect the metabolism of the probe drugs. Most patients identified as White (13 patients); 3 patients were Asian. The results suggest that goldenseal decreased metformin oral bioavailability by altering intestinal permeability, transport, and/or other processes involved in metformin absorption 1.
Common questions
Can I take Goldenseal and Metformin together?
Decreased metformin exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Goldenseal and Metformin 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 "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 Goldenseal or Metformin 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)
- Nguyen JT, Tian DD, Tanna RS, et al: Assessing transporter-mediated natural product-drug interactions via In vitro-in vivo extrapolation: clinical evaluation with a probe cocktail. Clin Pharmacol Ther 2021; 109(5):1342-1352.
Keep reading about Metformin
Keep reading about Goldenseal
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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