When you take Goldenseal (Hydrastis canadensis), a herbal supplement commonly used for immune support, it contains berberine, a compound that can interact with the diabetes medication metformin. This interaction may affect blood sugar control in people with type 2 diabetes. Understanding the goldenseal metformin interaction is crucial for managing your diabetes safely.
How the Interaction Works
The first major study on this interaction was published in February 2021 in Clinical Pharmacology & Therapeutics a peer-reviewed medical journal. Researchers from Washington State University, led by Dr. Mary Paine, found that goldenseal significantly reduces metformin absorption in the gut. This happens because goldenseal’s active compound, berberine, blocks intestinal transporters called organic cation transporter 1 (OCT1). These transporters are essential for moving metformin from your digestive tract into your bloodstream.
A follow-up study in February 2025 (Clinical and Translational Science a journal publishing clinical research) confirmed these findings. Scientists used blood and urine samples from adults with type 2 diabetes who were already taking metformin. After six days of goldenseal use, metformin levels dropped by 20-25% at lower doses. Crucially, the interaction occurs during intestinal absorption-not through liver metabolism or kidney excretion. This is different from earlier assumptions that goldenseal mainly affected liver enzymes like CYP3A (like grapefruit juice does).
Dose-Dependent Effects
| Metformin Dose | Effect on AUC | Effect on Cmax |
|---|---|---|
| 500-750 mg daily | 20% decrease | 25% decrease |
| 1000-1500 mg daily | 14% decrease | 14% decrease |
| 2000-2550 mg daily | No significant change | No significant change |
AUC (area under the curve) measures total drug exposure over time, while Cmax is the peak concentration in the blood. At lower metformin doses, goldenseal has the biggest impact. For example, if you take 500-750 mg daily, goldenseal can reduce metformin levels by up to 25%. Many people start on these doses, making this a serious concern. At higher doses (2000 mg+), the interaction disappears. But never assume higher doses are safe-your body may still absorb less metformin than expected.
The Dual Risk
Here’s where it gets complicated. Goldenseal contains berberine, which has its own blood sugar-lowering effects. Studies show berberine can reduce fasting glucose and HbA1c a measure of long-term blood sugar control levels when taken alone. This means when you combine it with metformin, two things happen: metformin absorption drops, but berberine tries to lower blood sugar. The result? Unpredictable blood sugar swings.
In the 2025 study, participants’ HbA1c improved slightly (from 6.8% to 6.5%) even with goldenseal use. But this doesn’t mean it’s safe. The researchers noted this improvement likely came from berberine, not metformin. If you stop goldenseal suddenly, your blood sugar could spike because metformin’s effectiveness has been reduced. This creates a dangerous cycle where your diabetes control becomes unstable.
What Medical Guidelines Say
The MSD Manual a trusted medical reference for healthcare professionals (2024 update) explicitly states: "Goldenseal may decrease the blood levels of metformin, potentially hindering glucose control in people with type 2 diabetes taking metformin." It also warns that berberine may increase hypoglycemic effects when combined with other diabetes medications.
The Merck Manual a widely used medical resource (Consumer Version, 2024) adds that berberine’s glucose-lowering effects are strongest in short-term use and diminish over time, especially in older adults. The American Diabetes Association a leading diabetes organization’s 2024 Standards recommend "routine assessment of all medications and supplements" for diabetes care. They don’t mention goldenseal specifically but stress that herbal supplements can interfere with prescription drugs.
What You Should Do
First, never stop taking metformin without talking to your doctor. If you’re currently using goldenseal, tell your healthcare provider immediately. They may need to adjust your metformin dose or monitor your blood sugar more closely. If you’re considering goldenseal for other health reasons, discuss safer alternatives. For example, some people use cinnamon or chromium supplements for blood sugar support, though these also have interactions. The key is to have a full medication review with your doctor.
Frequently Asked Questions
Can I take goldenseal while on metformin?
No. Medical guidelines strongly advise against combining goldenseal with metformin due to risks of unpredictable blood sugar levels. Even though berberine in goldenseal may lower blood sugar, the interaction can reduce metformin effectiveness, leading to dangerous fluctuations. Always consult your healthcare provider before using any supplements while on diabetes medication.
Why does goldenseal affect metformin?
Goldenseal blocks intestinal transporters (OCT1) that move metformin into your bloodstream. This reduces how much metformin your body absorbs. Unlike some drug interactions that happen in the liver, this effect occurs right in your gut during absorption.
Does the dose of metformin matter?
Yes. At lower doses (500-750 mg daily), goldenseal reduces metformin levels by 20-25%. At higher doses (2000 mg+), the effect disappears. But since many people start on lower doses, this is still a serious concern. Never assume higher doses are safe-your body may still absorb less metformin than expected.
What are the symptoms of this interaction?
You might notice unexplained high blood sugar levels despite taking your usual metformin dose. Alternatively, if you stop goldenseal suddenly, your blood sugar could spike because metformin’s effectiveness has been reduced. Always check your blood sugar regularly if you’re using both.
Is there a safe way to take goldenseal with metformin?
No. There’s no established safe timing or dosage for combining them. The interaction is unpredictable and can lead to dangerous blood sugar swings. Your doctor may recommend stopping goldenseal entirely or switching to a different supplement with no known interactions.
What about berberine supplements instead of goldenseal?
Berberine supplements also interact with metformin. They work similarly to goldenseal by blocking OCT1 transporters. Even pure berberine products can reduce metformin absorption. If you’re taking metformin, avoid all berberine-containing supplements.
How common is this interaction?
About 23% of U.S. adults use herbal supplements, and goldenseal is among the top 20 most used. With over 150 million people taking metformin globally, this interaction affects a significant number of patients. Many don’t realize they’re at risk.
What should I do if I accidentally took goldenseal with metformin?
Check your blood sugar more frequently for the next few days. Contact your doctor immediately if you notice unusual highs or lows. They may need to adjust your medication or monitor you closely.
Are there other supplements that interact with metformin?
Yes. St. John’s Wort, niacin, and certain herbal teas can also affect metformin. Always tell your doctor about every supplement you take. The American Diabetes Association recommends full medication reviews at every appointment.
Can I use goldenseal for colds while on metformin?
No. Even short-term use of goldenseal can disrupt your diabetes control. For colds, safer alternatives include saline nasal spray, honey, or acetaminophen (after checking with your doctor). Never use herbal remedies for minor issues without discussing them first.
