Berberine supplements: blood sugar evidence, side effects and drug interactions

Berberine has been part of traditional Chinese and Ayurvedic practice for centuries, and social media has repackaged it as a "natural alternative" to prescription glucose-lowering drugs. That framing implies equivalence, which no review supports, and glosses over differences in quality control, dosing and monitoring between a prescription medicine and a supplement.

Berberine-containing supplements may be made from Berberis species, Coptis rhizome, goldenseal or other plants, and some contain several alkaloids besides berberine. That means two products sold under the same name can differ in what they actually contain, which is one more reason a label alone is a poor guide.

A 2012 systematic review and meta-analysis in Evidence-Based Complementary and Alternative Medicine analysed fourteen randomised trials with 1,068 participants with type 2 diabetes. Berberine added to lifestyle modification produced a significant blood sugar and lipid-lowering response compared with lifestyle alone. Compared with oral drugs such as metformin, glipizide or rosiglitazone, berberine did not show significantly better glucose control but showed a mild lipid-lowering effect, and combined with the same drugs it gave better control than the drugs alone. No serious adverse effects were reported. The reviewers warned that evidence should be interpreted carefully because of low methodological quality, small sample sizes, few trials and unidentified risks of bias.

A 2015 meta-analysis in the Journal of Ethnopharmacology of 27 randomised trials with 2,569 patients examined berberine for type 2 diabetes, high lipids and hypertension, again finding favourable trends for glucose and lipid measures when berberine was added to lifestyle changes or to standard drugs. These are intermediate measures; they do not show fewer heart attacks, strokes or kidney complications.

The trials summarised in the two meta-analyses were mostly small, short and of generally low methodological quality, and they were designed to measure blood sugar and lipids rather than safety. That limits what can be said about long-term use, about higher doses, or about people with kidney, liver or heart conditions, who were not the focus of those studies.

The NHS states that not all herbal medicines are safe or suitable for everybody, and that you should check with a pharmacist before taking a herbal medicine if you already take other medicines. Berberine is usually sold as a food supplement or herbal product, and such products are not assessed for safety and interactions in the way a licensed medicine is, so the label alone cannot tell you whether it suits you.

• Side effects reported in the trials were mostly digestive, such as constipation, diarrhoea, nausea and abdominal pain, and were usually temporary.

• If you take medicines for diabetes, cholesterol, blood pressure or to prevent blood clots, ask a pharmacist or your prescriber before adding berberine.

• Tell your GP or diabetes team if you are taking berberine, so that changes in your blood sugar readings are interpreted correctly.

Many medicines are cleared from the body by liver enzymes, and substances that interfere with those enzymes can raise or lower the amount of a medicine in the blood. How far berberine does this is not settled in the sources reviewed for this guide, which is why a pharmacist check matters most for anyone on a medicine with a narrow safety margin, such as some transplant, epilepsy or heart medicines.

The NHS advises checking with a pharmacist before taking a herbal medicine if you already take other medicines, and says not all herbal products are safe or suitable for everybody. In practical terms, a glucose-lowering supplement taken on top of metformin, a sulfonylurea or insulin could deepen the effect on blood sugar, so low blood sugar is worth raising with your diabetes team before you start.

Berberine supplements are generally sold as food supplements in the UK. If marketed with claims to treat or manage diabetes, the MHRA may regard them as medicines, as it judges products by claims, ingredients and presentation. Food supplements are not required to demonstrate benefit before sale, and the MHRA states that herbal medicines registered through the THR scheme are the ones assessed for quality, safety and patient information.

Questions worth asking a seller: which plant and plant part, how much berberine per dose, whether batches are tested for contaminants, and where it is made. If you have diabetes, discuss it with your GP or diabetes team before starting; do not stop prescribed medicines, and keep monitoring glucose. Report suspected reactions on a Yellow Card.