Berberine Headache, Dizziness and Low Blood Sugar: Causes and What to Do

Why people ask about berberine and headaches

Berberine is a yellow alkaloid (a plant-derived compound) found in the roots, stems, rhizomes and bark of barberry (Berberis vulgaris), tree turmeric (Berberis aristata) and goldenseal (Hydrastis canadensis) [7]. It is sold in the UK as a food supplement, usually as capsules of a concentrated extract. ANSES notes that no health claims for berberine-containing plants are authorised at European level [3].

Because it can lower blood glucose, many people take berberine alongside a low-carbohydrate diet, and then notice a headache, light-headedness or a washed-out feeling an hour or two later. Those experiences are real, but the symptoms are shared by many conditions. A headache can follow a missed meal, too little fluid, poor sleep or caffeine withdrawal, whether or not a supplement is involved. Treating the supplement as the cause is a hypothesis, not a finding.

This article covers oral supplements only. Food supplements are not injected, and the evidence discussed here does not apply to any injected product. Anyone who has injected a berberine product and feels unwell should seek medical help.

How berberine could plausibly produce these symptoms

Think of the body as a house with several systems that can each cause a similar warning light. Dizziness, headache and fatigue are the warning light; berberine could trigger it through at least four different routes, and the routes call for different responses.

1. Lower blood glucose

Meta-analyses of randomised trials in type 2 diabetes show that berberine lowers fasting glucose, glucose after a meal and HbA1c, which is a blood test reflecting average glucose over the previous two to three months [1] [8] [9]. NHS information lists dizziness, tiredness or weakness, anxiety, sweating, shaking and heart palpitations among the symptoms of low blood sugar, and a diabetes service lists headaches too [2] [10]. If berberine pushed glucose low enough, those symptoms could follow. That is a mechanism-based expectation. It has not been shown to occur in people without diabetes.

2. Lower blood pressure or changes in heart rate

ANSES, the French food-safety agency, reviewed the clinical literature in 2019 and reported pharmacological effects of berberine from 400 mg a day in adults, including effects on blood pressure and heart rate, as well as on metabolism, the nervous system and immunity. It listed gastrointestinal disorders, hypoglycaemia and hypotension (low blood pressure) as risks [3]. Low blood pressure can cause light-headedness, especially on standing. ANSES does not quantify how often this happens.

3. Fluid loss from digestive side effects

Digestive upset is the side effect trials report most often. A 2014 summary of systematic reviews noted that adverse events in berberine trials were mostly gastrointestinal, such as constipation and diarrhoea [5]. In a 12-week randomised, placebo-controlled trial in newly diagnosed type 2 diabetes, berberine treatment induced more gastrointestinal side effects [11]. A hospital patient leaflet notes that heavy fluid loss in diarrhoea can lead to dehydration, which can be serious if it is not recognised and treated [12]. Loose stools followed by dizziness is therefore a pairing worth considering before blaming blood sugar.

4. Medicine interactions

In a human study, healthy male volunteers took berberine 300 mg three times daily for two weeks. Tests with probe drugs showed reduced activity of the liver enzymes CYP2D6, CYP2C9 and CYP3A4, which break down many medicines. For CYP2D6, the urinary ratio used to measure activity rose ninefold, and the CYP2C9 marker ratio roughly doubled [6]. Those are pharmacokinetic changes (how the body handles a drug), not proof of harm. They mean a person on prescribed medicines could have higher medicine levels than expected, and symptoms such as dizziness might come from the medicine rather than from berberine itself. ANSES also calls for extreme vigilance because of the numerous interactions identified [3].

What the clinical evidence shows

Headache and dizziness

Searches of the trial summaries available for this article found no randomised trial that set out to measure headache or dizziness caused by berberine. Two systematic reviews summarised in 2014 described adverse events as mostly gastrointestinal and found no significant difference between berberine and control groups; in one of them, three of 14 trials did not report adverse events at all [5]. Some consumer health sites list headache and dizziness as less common effects, but those lists do not identify trial data behind them. The honest position is that headache and dizziness are possible, uncommon or under-reported, and unquantified.

Hypoglycaemia in people with type 2 diabetes

The best numerical evidence comes from a 2022 meta-analysis of 37 randomised trials with 3,048 participants who had type 2 diabetes. Berberine, alone or with other oral glucose-lowering drugs, lowered fasting glucose by 0.82 mmol/L on average and HbA1c by 0.63 percentage points. For hypoglycaemia, the relative risk was 0.48 (95% confidence interval 0.21 to 1.08, P = 0.08), meaning the analysis did not detect a statistically significant increase [1].

That result needs careful reading. A confidence interval running up to 1.08 cannot rule out a modest increase, and a P value of 0.08 is not evidence of safety. The trials also differ in dose, duration and comparator, and earlier systematic reviews judged many berberine trials to be at high risk of bias [5]. The authors report that the glucose-lowering effect was associated with baseline fasting glucose and HbA1c [1]. ANSES, taking a precautionary view, still advises people with diabetes to avoid berberine supplements [3].

Can berberine cause low blood sugar in people without diabetes?

The trials above enrolled people with type 2 diabetes, so they do not answer this question. The NHS states that low blood sugar usually affects people with diabetes who take insulin or certain other diabetes medicines, and that it is rare in people without diabetes [2]. No trial evidence reviewed here shows berberine causing hypoglycaemia in people with normal glucose control. The meta-analysis authors cite the view that berberine’s glucose-lowering action occurs under hyperglycaemic conditions [1]. That is a proposed mechanism rather than a demonstrated finding in healthy people, so an absence of data is not proof of safety. The combination to be most cautious about is berberine with glucose-lowering prescription medicines, where effects could add together. ANSES’s advice for people with diabetes to avoid berberine reflects that concern [3].

Reactive hypoglycaemia after a low-carbohydrate meal

Reactive hypoglycaemia means a low glucose reading a few hours after eating. No study found tests berberine together with low-carbohydrate meals, and no source reviewed describes reactive hypoglycaemia as a berberine effect. Someone who feels shaky or foggy a few hours after a small, low-carbohydrate meal has a simple explanation already available: not much food. The only reliable way to tell is to measure glucose at the time of symptoms. People without a meter can ask a GP about testing, because the NHS advises seeing a GP when someone without diabetes has symptoms such as shaking, sweating, a fast heartbeat and confusion [2].

Practical steps if you feel unwell

If you suspect low blood sugar

For people with diabetes, the NHS advises checking blood sugar if possible. If it is below 4 mmol/L, eat or drink something that raises it quickly, such as a small glass of fruit juice or sugary fizzy drink, five glucose or dextrose tablets, four large jelly babies or two tubes of glucose gel. Recheck after 10 to 15 minutes, repeat if still below 4 mmol/L, and once symptoms improve eat something longer-acting such as biscuits, a sandwich or the next meal [2]. That is guidance written for people with diabetes. Someone without diabetes who has repeated episodes should see a GP rather than self-treat, because the underlying cause matters.

Do not give food or drink to anyone who has become unconscious. The NHS advice is to put them in the recovery position and call 999 [2].

If you feel dizzy or light-headed

Sit or lie down, drink water if you can, and note whether you have had diarrhoea or have eaten. The NHS advises calling 999 or going to A&E for heart palpitations with chest pain, shortness of breath, dizziness or light-headedness, or fainting [4].

If you feel tired, weak or foggy

Tiredness and weakness appear on the NHS list of low-blood-sugar symptoms [2], but they also accompany dehydration, poor sleep and many illnesses. No trial evidence links berberine to brain fog. A reasonable approach is to stop the supplement while you seek advice, rather than adjusting doses repeatedly on your own, particularly if you take prescribed medicines.

Electrolyte loss versus a berberine effect

Electrolytes are salts such as sodium and potassium that the body needs for muscle and nerve function. No study identified for this article shows that berberine directly depletes electrolytes. The more established route is indirect: berberine can cause loose stools [5], and diarrhoea itself causes loss of fluid and salts [12]. If weakness arrives with diarrhoea, thirst or dark urine, fluid loss is a better explanation than a hypothetical direct effect. A hospital leaflet advises that a GP or pharmacist may suggest an oral rehydration solution, available as sachets from a pharmacy, for people at risk of dehydration [12]. Diarrhoea that persists, or any symptoms that worry you, deserve a call to 111 or your GP.

Dose, timing and product quality

There is no UK-authorised intake for berberine. In the small 2008 type 2 diabetes trial, participants took 500 mg three times daily for 13 weeks in one study arm; when gastrointestinal side effects were heavy the dose was reduced to 300 mg three times daily [14]. ANSES reports pharmacological effects from 400 mg a day in adults and says lower doses cannot be ruled out [3]. That is a research and regulatory reference point, not a recommendation.

Oral berberine is poorly absorbed, with bioavailability reported as below 1% [15]. Product quality is another source of uncertainty: in a survey of 15 US-market supplements the average berberine content was 75% of the label claim, with a wide range between products [7]. Two people taking the same labelled dose may therefore receive different amounts. A companion Vetted Therapeutics article explains how to read a certificate of analysis.

Frequently asked questions

Editorial summary

What is established: berberine lowers glucose in people with type 2 diabetes, causes digestive side effects, inhibits several drug-metabolising enzymes in volunteers, and is the subject of a precautionary regulatory warning in France that lists hypoglycaemia and hypotension among its risks [1] [6] [3]. What is uncertain: how often it causes headache, dizziness or fatigue, whether it can cause hypoglycaemia in people with normal glucose control, and which of several explanations applies to any one person. What it means in practice: treat the symptoms on their own terms, measure glucose when you can, replace fluids after diarrhoea, and involve a pharmacist or GP if you take medicines or the symptoms recur.

References

1. Xie W, Su F, Wang G, et al. Glucose-lowering effect of berberine on type 2 diabetes: a systematic review and meta-analysis. Frontiers in Pharmacology. 2022;13:1015045. https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2022.1015045
2. NHS. Low blood sugar (hypoglycaemia). NHS website. https://www.nhs.uk/conditions/low-blood-sugar-hypoglycaemia/
3. ANSES (French Agency for Food, Environmental and Occupational Health & Safety). Use of berberine-containing plants in food supplements. 25 November 2019. https://www.anses.fr/en/news/use-berberine-containing-plants-food-supplements
4. NHS. Heart rhythm problems (arrhythmia). NHS website. https://www.nhs.uk/conditions/arrhythmia/
5. Table 1: A summary of findings from systematic reviews on the antihyperglycemic effects of berberine (summarising Dong et al. 2012 and Narenqimuge et al. 2012). 2014; doi:10.1155/2014/798093. https://pmc.ncbi.nlm.nih.gov/articles/PMC4003828/table/tab1
6. Guo Y, Chen Y, Tan Z-R, Klaassen CD, Zhou H-H. Repeated administration of berberine inhibits cytochromes P450 in humans. European Journal of Clinical Pharmacology. PMID 21870106. https://pmc.ncbi.nlm.nih.gov/articles/PMC4898966
7. Funk RS, Singh RK, Winefield RD, et al. Variability in potency among commercial preparations of berberine. PubMed Central PMC5807210. https://pmc.ncbi.nlm.nih.gov/articles/PMC5807210
8. Effects of berberine on blood glucose in patients with type 2 diabetes mellitus: a systematic literature review and a meta-analysis. Endocrine Journal. 2019;66(1):51-63. https://www.jstage.jst.go.jp/article/endocrj/66/1/66_EJ18-0109/_article
9. NHS. HbA1c test (haemoglobin A1c). NHS website. https://www.nhs.uk/tests-and-treatments/haemoglobin-a1c-hba1c-test/
10. NHS Tayside. Low blood glucose (hypoglycaemia). Diabetes Out There Tayside. https://www.nhstayside.scot.nhs.uk/OurServicesA-Z/DiabetesOutThereDOTTayside/PROD_263748
11. Zhang Y, Gu Y, Ren H, et al. Gut microbiome-related effects of berberine and probiotics on type 2 diabetes (the PREMOTE study). Nature Communications. 2020. https://doi.org/10.1038/s41467-020-18414-8
12. University Hospital Southampton NHS Foundation Trust. Diarrhoea: patient information factsheet. https://uhs.nhs.uk/Media/UHS-website-2019/Patientinformation/Generalmedicine/Diarrhoea-1360-PIL.pdf
13. University Hospitals Sussex NHS Foundation Trust. Heart palpitations: patient information. https://www.uhsussex.nhs.uk/?p=2910
14. Yin J, Xing H, Ye J. Efficacy of berberine in patients with type 2 diabetes mellitus. Metabolism. 2008;57(5):712-717. https://pmc.ncbi.nlm.nih.gov/articles/PMC2410097/
15. Absorption kinetics of berberine and dihydroberberine and their impact on glycemia: a randomized, controlled, crossover pilot trial. PMID 35010998. https://pubmed.ncbi.nlm.nih.gov/35010998/
16. MHRA. Herbal and homeopathic medicines: reminder to be vigilant for suspected adverse reactions and to report them to the Yellow Card scheme. Drug Safety Update, 7 July 2021. https://www.gov.uk/drug-safety-update/herbal-and-homeopathic-medicines-reminder-to-be-vigilant-for-suspected-adverse-reactions-and-to-report-them-to-the-yellow-card-scheme