Some can, modestly. Berberine has the most consistent evidence, with meta-analyses of randomized trials showing reductions in fasting glucose and A1C in people with type 2 diabetes — though most trials are small, short and of variable quality. Chromium, cinnamon, alpha-lipoic acid and magnesium have weaker or mixed evidence, with benefit most likely in people who are deficient. No supplement lowers glucose as much as medication or meaningful weight loss, none has been shown to prevent complications, and several can cause low blood sugar when combined with diabetes drugs. Nothing here should replace prescribed treatment.
The short answer
Yes, some supplement ingredients lower blood glucose in human trials — but "lower" needs qualifying. The reductions are modest, the trials are mostly small and short, quality varies a great deal, and no supplement has been shown to reduce the heart, kidney, eye or nerve complications that are the reason glucose control matters. Medication and weight loss have far larger and better-established effects.
The rest of this page goes through the ingredients that are studied most, rates the evidence for glucose specifically, and covers the safety issues that a label rarely mentions.
How we rate the evidence
Ratings below reflect human trials for the specific outcome of blood glucose or A1C, using the scale on our how we research page: strong, moderate, limited, mixed or insufficient. An ingredient can be well studied for one purpose and poorly studied for another; these ratings apply to glucose only.
Ingredient by ingredient
Berberine — Moderate
Berberine is a plant alkaloid extracted from goldenseal, barberry and other plants. Several meta-analyses of randomized trials in people with type 2 diabetes report reductions in fasting glucose and A1C, with effect sizes in the region of those seen with some oral diabetes medications in the same trials. Typical doses studied are 900–1,500 mg per day in divided doses.
The caveats are substantial. Most trials were conducted in China, were short (three months is typical), and many had methodological weaknesses. Long-term safety data are lacking. Gastrointestinal side effects — constipation, diarrhoea, cramping — are common. Berberine inhibits several liver enzymes (including CYP3A4 and CYP2D6) that process many prescription drugs, and it can lower glucose enough to cause hypoglycemia alongside insulin or sulfonylureas. It should not be used in pregnancy or breastfeeding.
Chromium — Mixed
Chromium is a trace mineral involved in insulin signalling. Trials of chromium picolinate in type 2 diabetes have produced inconsistent results: some meta-analyses find small reductions in fasting glucose and A1C, others find no meaningful effect. Benefit, where it appears, seems concentrated in people with poor glucose control or low chromium status. Doses in trials range widely, from 200 to 1,000 micrograms per day. Chromium is generally well tolerated at those doses.
Cinnamon — Mixed
Cinnamon has been tested in dozens of small trials with contradictory findings; some meta-analyses report modest reductions in fasting glucose, others none. Trials use different species, doses and preparations, which makes them hard to compare. Cassia cinnamon, the common kind, contains coumarin, which can harm the liver in large amounts; Ceylon cinnamon contains much less. A trial dose of 1–6 grams of cassia per day approaches the coumarin limits for smaller adults.
Alpha-lipoic acid — Limited for glucose
Alpha-lipoic acid is an antioxidant involved in energy metabolism. Its best evidence is not for glucose but for the symptoms of diabetic neuropathy, where intravenous and oral doses of 600 mg per day have reduced pain and numbness in several trials. Effects on glucose and insulin sensitivity have been small and inconsistent. It can lower glucose enough to matter in combination with medication and can interfere with thyroid hormone in some people.
Magnesium — Limited
Low magnesium is common in type 2 diabetes, partly because high glucose increases magnesium loss in urine, and low magnesium worsens insulin resistance. Supplementation improves glucose and insulin sensitivity in trials of people who are magnesium-deficient; benefit in people with normal magnesium is small or absent. Doses of 250–400 mg per day are typical. Large doses cause diarrhoea; magnesium should be used with care in kidney disease.
Gymnema sylvestre — Limited
A herb used in traditional Indian medicine; extracts are reported to reduce sugar absorption and support insulin release. A small number of trials suggest reduced glucose and A1C, but they are old, small and mostly uncontrolled. It can add to the effect of diabetes medication.
Bitter melon — Insufficient
Bitter melon (Momordica charantia) contains compounds with insulin-like activity in the laboratory. Human trials are few, small and mostly negative or inconclusive. It has caused hypoglycemia in case reports and is not recommended in pregnancy.
Fenugreek — Limited
Fenugreek seed is high in soluble fibre and has reduced fasting glucose in a handful of small trials, probably by slowing carbohydrate absorption. Doses studied are large (5–25 grams of seed powder daily) and the evidence is weak.
Vitamin D — Mixed
Low vitamin D is associated with diabetes risk in observational studies, but supplementation trials have been largely disappointing. A large trial in people with prediabetes found a small, statistically borderline reduction in progression to diabetes; effect in established diabetes is minimal. Correcting a documented deficiency is sensible for other reasons.
Fibre supplements — Moderate
Soluble fibre such as psyllium or glucomannan, taken before meals, slows glucose absorption and modestly reduces after-meal and fasting glucose in trials. This is one of the better-supported and safest options, and it overlaps with dietary advice: see fibre and blood sugar.
What the evidence does not show
- No supplement has been shown to reduce diabetes complications — heart attack, stroke, kidney failure, blindness or amputation. Those are what glucose control is for, and only medication, weight loss and blood pressure and cholesterol management have that evidence.
- Finished products are almost never studied. The trials above tested single ingredients at defined doses. Commercial blood-sugar supplements combine several ingredients, often at lower or undisclosed doses in "proprietary blends". Evidence for the ingredients is not evidence for the product.
- Effects in people with normal glucose are minimal. Most trials enrolled people with diabetes; there is little reason to expect a glucose-lowering effect in someone whose glucose is already normal.
Safety considerations
Talk to your doctor or pharmacist before starting any glucose-lowering supplement, particularly if you take insulin, sulfonylureas (glipizide, gliclazide, glimepiride) or other glucose-lowering medication. Combining them can cause hypoglycemia. Berberine and some herbs also change how the liver processes other medicines.
Dietary supplements in the United States are not approved by the FDA before sale and are not required to prove effectiveness. Independent testing has repeatedly found products that contain less of an ingredient than the label states, or undeclared pharmaceutical drugs. Choosing products tested by an independent laboratory (USP, NSF, ConsumerLab) reduces that risk.
Where this leaves you
If you have prediabetes or type 2 diabetes, the interventions with the strongest evidence remain the least glamorous: losing 5–10% of body weight, 150 minutes a week of activity, a higher-fibre eating pattern, adequate sleep, and the medications your doctor prescribes. A supplement can sit alongside those, with your care team's knowledge, but it cannot stand in for them.
Our blood sugar supplement research pages evaluate specific commercial products on formula, dose transparency and evidence, and contain affiliate links with disclosure.
Frequently asked questions
Is berberine "natural metformin"?
Berberine and metformin share some overlapping actions on the liver and on cellular energy sensing, and trials show berberine lowers glucose. But metformin has decades of large trials showing it reduces complications and is safe long-term; berberine has neither. Calling it natural metformin overstates the evidence and understates the differences.
Can I stop my diabetes medication if I take supplements?
No. No supplement has been shown to replace glucose-lowering medication, and stopping medication can lead to dangerous rises in glucose. Any change to medication should be made with your prescriber.
Which supplements should I avoid with diabetes medication?
Anything that lowers glucose — berberine, cinnamon, chromium, alpha-lipoic acid, gymnema, bitter melon, fenugreek — can add to the effect of insulin or sulfonylureas and cause hypoglycemia. Berberine also affects liver enzymes that process many drugs. Discuss all supplements with a pharmacist.
Do blood sugar supplements work for prediabetes?
Evidence in prediabetes is thinner than in diabetes. Lifestyle change reduced progression to diabetes by 58% in the Diabetes Prevention Program; no supplement has a comparable result.
References
- National Center for Complementary and Integrative Health (NCCIH). Diabetes and Dietary Supplements: What You Need To Know (2021). https://www.nccih.nih.gov/health/diabetes-and-dietary-supplements-what-you-need-to-know
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Type 2 Diabetes (2023). https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/type-2-diabetes
- U.S. Food and Drug Administration. Dietary Supplements (2024). https://www.fda.gov/food/dietary-supplements
This page discusses supplement ingredients or categories. It may mention a commercial product, with disclosure. It is general health information, not personal medical advice. Read our editorial policy and medical review policy.