Berberine Side Effects: 3 Drug-Clearing Enzymes Slowed in 2 Weeks

Q: How big is that, by FDA's own scale?

The US Food and Drug Administration grades enzyme inhibitors by how much they raise the blood level (AUC) of a sensitive test drug. A weak inhibitor raises it "≥1.25-fold to <2-fold", a moderate one "≥2-fold to < 5-fold", and a strong one "≥5-fold". The 40% rise in midazolam is 1.4-fold, which falls in FDA's weak range for CYP3A4. The CYP2D6 and CYP2C9 results were measured as urine or metabolite ratios rather than as AUC, so they cannot be placed on that scale; the ninefold change in the CYP2D6 ratio is large, but it is not the same thing as a ninefold rise in a drug's blood level.

Q: What are the most common side effects of berberine?

Digestive ones: constipation, diarrhoea, nausea, bloating and abdominal pain. In a 2008 pilot, 20 patients (34.5%) had transient gastrointestinal effects; in a 116-person trial, five people taking berberine had mild to moderate constipation.

Q: Does berberine damage the liver?

Not on current evidence. LiverTox says berberine "has not been linked to serum aminotransferase elevations during therapy nor to instances of clinically apparent liver injury," and a meta-analysis of 10 trials in fatty liver disease found liver enzymes fell.

Q: Which medications should not be taken with berberine?

The one interaction measured in patients is cyclosporine, whose levels ended 29.3% higher in transplant recipients taking berberine. In healthy volunteers, berberine also slowed CYP2D6, CYP2C9 and CYP3A4, the enzymes that clear drugs such as dextromethorphan, metoprolol, warfarin, celecoxib, simvastatin and midazolam. Diabetes and blood-pressure medicines can add to berberine's own effects. Ask a pharmacist to check your list.

Q: Can berberine cause low blood sugar?

Berberine lowers blood sugar on its own; in one pilot its effect was similar to metformin at the same dose. Combined with diabetes medicines, the effects add, which is why a 2026 interaction review lists hypoglycemia among berberine's interactions. Any change to diabetes treatment should be made with your doctor.

Q: Is berberine safe during pregnancy or breastfeeding?

NCCIH says berberine is "likely to be unsafe for infants and may also be unsafe for use during pregnancy or while breastfeeding," because it has been linked to a harmful buildup of bilirubin in newborns. There are no trials in pregnancy.

Q: How long do berberine side effects last?

The trials describe the digestive effects as transient. The enzyme effects are different: they were measured after 2 weeks of continuous use, and the study did not measure how quickly they wear off after stopping. Assume the effect on other medicines lasts at least as long as you keep taking berberine.

29 Oct 2026·HealthyMag Editorial Team

Yellow berberine powder in a white dish beside dried barberry root

Quick Answer: The side effects of berberine that people notice are digestive: constipation, diarrhoea, bloating and cramping. In a 2008 pilot, 20 patients (34.5%) had transient gastrointestinal effects, and across 10 trials in fatty liver disease (811 patients) only mild digestive events were reported. The liver itself has a clean record: the US government’s LiverTox database says berberine “has not been linked” to liver enzyme rises or to clinically apparent liver injury. The side effect you will not feel is the one that matters if you take prescription medicine. After 2 weeks at 300 mg three times a day, berberine slowed 3 of the 5 drug-clearing liver enzymes tested in healthy volunteers: a CYP2D6 marker rose ninefold, a CYP2C9 marker doubled, and the CYP3A4 marker drug midazolam reached 40% higher blood levels. In kidney-transplant patients, adding berberine left cyclosporine levels 29.3% higher than in patients who did not take it.

This page is about safety: what berberine does to the stomach, the liver, other medicines, blood sugar, and newborns. It does not try to settle whether berberine works; our berberine evidence review covers the blood sugar and weight trials.

Berberine side effects: what the evidence shows

Question	Best evidence	What it found
Stomach and bowel	Pilot trial (2008); randomised trial of 116 (2008); meta-analysis of 10 trials	34.5% transient digestive effects in one pilot; constipation in 5 people in the other trial; “only mild” events in the meta-analysis
Liver	LiverTox (NIDDK), updated 2020	No liver enzyme rises and no cases of clinically apparent liver injury on record
Other medicines	Crossover study, 17 healthy men; transplant trial, 104 patients	3 of 5 enzymes slowed in 2 weeks; cyclosporine 29.3% higher than in controls
Blood sugar and blood pressure	Narrative review of interactions (2026)	Effects add to those of diabetes and blood-pressure medicines
Newborns and pregnancy	NCCIH; Singapore ban 1978 and its review	“Likely to be unsafe for infants”; no trials in pregnancy

The side effects you will feel: stomach and bowel

Every source that lists berberine’s side effects puts the gut first. The National Center for Complementary and Integrative Health (NCCIH) says the side effects reported in research studies are “primarily gastrointestinal symptoms such as nausea, abdominal pain, bloating, constipation, or diarrhea.”

How often that happens depends on the trial. In a 2008 pilot from Shanghai, berberine was given at 0.5 g three times a day; the authors report that “20 (34.5%) patients experienced transient gastrointestinal adverse effects,” and that no liver or kidney damage was seen in any patient. In a placebo-controlled trial of 116 people with type 2 diabetes published the same year, berberine at 1.0 g a day for 3 months produced “mild to moderate constipation” in five participants in the berberine group, and nothing else was listed. A 2024 meta-analysis of 10 randomised trials in non-alcoholic fatty liver disease, with 811 patients, concluded that berberine had “a favorable safety profile, with only mild gastrointestinal adverse events reported.”

Two things follow. The digestive effects are common enough that a sizeable minority of people will notice them, and the trials describe them as mild and passing. And they tell you nothing about the risk that is harder to see, because a medicine whose blood level has risen does not announce itself in your stomach.

The liver: a cleaner record than most supplements

Many searches for berberine side effects ask about liver damage. LiverTox, the drug-induced liver injury database run by the National Institute of Diabetes and Digestive and Kidney Diseases, is direct about it: berberine “has not been linked to serum aminotransferase elevations during therapy nor to instances of clinically apparent liver injury.” The fatty liver meta-analysis above found liver enzymes fell rather than rose in the berberine groups, and the 2008 pilot reported no liver damage.

That record covers berberine itself. It does not cover the other herbs that are often blended into berberine products, which have their own safety profiles and are usually not tested in the trials.

The side effect you will not feel: 3 enzymes slowed in 2 weeks

Your liver and gut clear most prescription drugs through a family of enzymes called cytochrome P450 (CYP). If something slows one of those enzymes, any drug that depends on it stays in your blood longer and at a higher level. You feel nothing from the slowing itself; you may feel the higher drug level.

The clearest human test of berberine on these enzymes was published in the European Journal of Clinical Pharmacology in 2012. Eighteen healthy Chinese men entered a randomised crossover study and 17 completed it. Each took berberine 300 mg three times a day for 2 weeks and, in a separate period with a 4-week washout, a placebo. At the end of each period they were given five “probe” drugs, each one cleared mainly by a single enzyme, so that the change in the probe shows the change in the enzyme.

Enzyme	Probe drug	Change after 2 weeks of berberine	Examples of drugs FDA lists as sensitive to this enzyme
CYP2D6	Dextromethorphan	Urinary dextromethorphan/dextrorphan ratio rose ninefold (P < 0.01)	Dextromethorphan, desipramine, nebivolol; metoprolol (moderately sensitive)
CYP2C9	Losartan	Losartan/E-3174 ratio doubled (P < 0.01)	Celecoxib; warfarin and tolbutamide (moderately sensitive)
CYP3A4	Midazolam	Peak level +38%, total exposure (AUC) +40%, oral clearance −27%	Midazolam, simvastatin, tacrolimus
CYP2C19	Omeprazole	No significant change	—
CYP1A2	Caffeine	No significant change	—

The authors’ conclusion was short: “Drug-drug interactions should be considered when berberine is administered.”

How big is that, by FDA’s own scale?

The US Food and Drug Administration grades enzyme inhibitors by how much they raise the blood level (AUC) of a sensitive test drug. A weak inhibitor raises it “≥1.25-fold to <2-fold”, a moderate one “≥2-fold to < 5-fold”, and a strong one “≥5-fold”. The 40% rise in midazolam is 1.4-fold, which falls in FDA’s weak range for CYP3A4. The CYP2D6 and CYP2C9 results were measured as urine or metabolite ratios rather than as AUC, so they cannot be placed on that scale; the ninefold change in the CYP2D6 ratio is large, but it is not the same thing as a ninefold rise in a drug’s blood level.

Berberine does not appear on FDA’s table of example drugs and substances that interact with these enzymes, which was current as of 29 May 2026. The table does include five non-drugs: St. John’s wort, curcumin, diosmin, tobacco smoke and grapefruit juice. FDA describes the list as “a guide and not considered a comprehensive list”, so the absence is not a clearance; it means a pharmacist checking a printed interaction list may not see berberine flagged at all.

What this study cannot tell you

The volunteers were 17 young men (average age 21.6) taking no other medicines, at a total of 900 mg a day. The authors note that “the individual variability was relatively large,” and suggest the effect “might be genotype-dependent.” So the study shows the enzymes slow in healthy people at a common dose; it does not show how large the effect is in an older person taking several medicines, or at the higher daily amounts some products recommend.

The only interaction measured in patients: cyclosporine after a transplant

The one drug interaction tested in real patients is with cyclosporine, the anti-rejection drug used after organ transplants, whose dose is normally adjusted to measured blood levels. In a 2005 trial from Wuhan, 52 kidney-transplant recipients took cyclosporine plus berberine 0.2 g three times a day for 3 months, and another 52 took cyclosporine alone.

Cyclosporine trough levels rose 88.9% from baseline with berberine, against 64.5% without it.
At the end, levels in the berberine group were 29.3% higher than in the berberine-free group (P < 0.05).
In a smaller pharmacokinetic study of 6 patients over 12 days, cyclosporine exposure (AUC) rose 34.5% and its clearance fell 40.4%.
No significant effect on liver or kidney function was seen.

The authors read this as a possible advantage: “This combination may allow a reduction of the CsA dosage.” That is a decision for a transplant team measuring blood levels. For someone who adds a supplement without telling them, the same number means a drug level moving by almost a third with nobody checking. NCCIH names cyclosporine as its example interaction and advises anyone taking medicine to talk with a health care provider before taking berberine.

Blood sugar and blood pressure: effects that add up

Not every interaction runs through liver enzymes. A 2026 narrative review of berberine-drug interactions describes “pharmacodynamic additivity (hypoglycemia, hypotension, and QT prolongation)” as one of four ways berberine can interact, and notes that the interactions are “documented in humans for a few pairs and mechanistic for most.” In plain terms, berberine lowers blood sugar on its own, so adding it to insulin, a sulfonylurea or other glucose-lowering medicine stacks two effects in the same direction.

How large is berberine’s own effect? In the 2008 Shanghai pilot, newly diagnosed patients were randomised to berberine or metformin at the same 0.5 g three times a day, and “the hypoglycemic effect of berberine was similar to that of metformin.” The review’s conclusion is that in people taking several medicines, berberine “should be managed as an active pharmacological perpetrator rather than as an inert supplement.” If you take a diabetes or blood-pressure medicine, this is a conversation for your doctor before you start, because any adjustment depends on your readings and your prescription.

Newborns and pregnancy: where the strongest warning comes from

NCCIH’s strongest safety statement is about babies: “Exposure to berberine has been linked to a harmful buildup of bilirubin in infants, which can cause brain damage. Therefore, berberine is likely to be unsafe for infants and may also be unsafe for use during pregnancy or while breastfeeding.”

The history behind it is specific. In 1978, Singapore banned Rhizoma coptidis (huanglian), a berberine-containing herb, and berberine itself after the herb was implicated in neonatal jaundice and kernicterus in newborns with glucose-6-phosphate dehydrogenase (G6PD) deficiency, an inherited enzyme deficiency. More than three decades later, Singapore’s Health Sciences Authority reviewed the evidence and lifted the ban.

Part of the evidence for that review came from adults. A Singapore General Hospital study analysed 20 patients with chronic blood disorders whose herbal treatment contained berberine herbs, covering 1,055 patient-days of one herb and 1,252 of the other. It found “no organ toxicity or electrolyte imbalance”; three patients with thalassemia intermedia had a transient rise in bilirubin without worsening anaemia or liver function. The authors also wrote that the literature gave “conflicting evidence of varying levels either supporting or refuting” the newborn link.

So the reassuring data are in adults, and the warning is about newborns. There are no trials of berberine in pregnancy. The lifting of a ban on a traditional herb is not evidence that a concentrated supplement is safe for a fetus or a breastfed baby, and NCCIH’s caution stands.

Herbal Lab Berberine Liquid Drops. An alcohol-free liquid with a 1,800 mg proprietary blend per 2 ml serving, combining berberine HCl with barberry, Ceylon cinnamon, gymnema, bitter melon, fenugreek, turmeric, banaba, black pepper and chromium. This is a paid placement, not a recommendation, and it does not change the safety summary above: none of the studies on this page tested this product, and the label does not state how much of the blend is berberine, so its dose cannot be compared with the 900 mg a day used in the enzyme study. The interaction findings on this page apply to berberine in any form.

View on Herbal Lab (code HERBAL15)

Sponsored link — we may earn a commission at no extra cost to you. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. If you take prescription medicine, especially for diabetes, blood pressure or after a transplant, or are pregnant or breastfeeding, ask your doctor or pharmacist first.

Who should talk to a doctor or pharmacist first

Anyone taking cyclosporine, tacrolimus or another drug that needs blood-level monitoring.
Anyone taking insulin, a sulfonylurea or other diabetes medicine, or medicine for blood pressure.
Anyone taking a drug cleared by CYP2D6, CYP2C9 or CYP3A4; a pharmacist can tell you which of your medicines fall into these groups.
People who are pregnant or breastfeeding, and anyone thinking of giving berberine to a baby or child.
Anyone taking a berberine blend with several other herbs, since the trials above tested berberine alone.

Frequently Asked Questions

What are the most common side effects of berberine?

Digestive ones: constipation, diarrhoea, nausea, bloating and abdominal pain. In a 2008 pilot, 20 patients (34.5%) had transient gastrointestinal effects; in a 116-person trial, five people taking berberine had mild to moderate constipation.

Does berberine damage the liver?

Not on current evidence. LiverTox says berberine “has not been linked to serum aminotransferase elevations during therapy nor to instances of clinically apparent liver injury,” and a meta-analysis of 10 trials in fatty liver disease found liver enzymes fell.

Which medications should not be taken with berberine?

The one interaction measured in patients is cyclosporine, whose levels ended 29.3% higher in transplant recipients taking berberine. In healthy volunteers, berberine also slowed CYP2D6, CYP2C9 and CYP3A4, the enzymes that clear drugs such as dextromethorphan, metoprolol, warfarin, celecoxib, simvastatin and midazolam. Diabetes and blood-pressure medicines can add to berberine’s own effects. Ask a pharmacist to check your list.

Can berberine cause low blood sugar?

Berberine lowers blood sugar on its own; in one pilot its effect was similar to metformin at the same dose. Combined with diabetes medicines, the effects add, which is why a 2026 interaction review lists hypoglycemia among berberine’s interactions. Any change to diabetes treatment should be made with your doctor.

Is berberine safe during pregnancy or breastfeeding?

NCCIH says berberine is “likely to be unsafe for infants and may also be unsafe for use during pregnancy or while breastfeeding,” because it has been linked to a harmful buildup of bilirubin in newborns. There are no trials in pregnancy.

How long do berberine side effects last?