Also indexed as: Glucophage
Try these helpful products which may be beneficial if taken with this medicine
- Vitamin B12 and folic acid
- To avoid depleting these nutrients, which might lead to anemia and high homocysteine blood
levels, take 1,000 mcg of vitamin B12 and 400 mcg of folic acid daily
- The vitamin B12– and folic acid–depleting effect of metformin might be
prevented by supplementing with calcium; take 800 to 1,000 mg daily
- Chromium supplements have been shown to improve blood sugar control in people with
diabetes, but should only be combined with metformin under a doctor’s supervision
These recommendations are not comprehensive and are not intended to
replace the advice of your doctor or pharmacist. Continue reading the full article for more
information on interactions with vitamins, herbs, and foods.
Interactions with Vitamins, Herbs, and Foods
In some cases, an herb or supplement may appear in more than one category, which may seem
contradictory. For clarification, read the full article for details about the summarized
| May Be Beneficial: Depletion or
interference—The medication may deplete or interfere with the absorption or
function of the nutrient. Taking these nutrients may help replenish them.
| May Be Beneficial: Side effect
reduction/prevention—Taking these supplements may help reduce the likelihood and/or
severity of a potential side effect caused by the medication.
Avoid: Reduced drug absorption/bioavailability—Avoid these supplements
when taking this medication since the supplement may decrease the absorption and/or activity
of the medication in the body.
Avoid: Adverse interaction—Avoid these supplements when taking this
medication because taking them together may cause undesirable or dangerous results.
Check: Other—Before taking any of these supplements or eating any of
these foods with your medication, read this article in full for details.
An asterisk (*) next to an item in the summary indicates that the
interaction is supported only by weak, fragmentary, and/or contradictory scientific
Interactions with Dietary Supplements
Chromium supplements have been shown to improve blood sugar control in people with
diabetes.1 Consequently, supplementing with chromium could reduce blood sugar
levels in people with taking metformin, potentially resulting in abnormally low blood sugar
levels (hypoglycemia). While chromium
supplementation may be beneficial for people with
diabetes, its use in combination with metformin or with any other blood sugar-lowering
medication should be supervised by a doctor.
Metformin has been reported to increase blood levels of DHEA-sulfate in at least two
Folic acid and Vitamin B12
Metformin therapy has been shown to deplete vitamin B12 and sometimes, but not
always,4 folic acid as well.5 This depletion occurs through the
interruption of a calcium-dependent mechanism. Supplementation with calcium has reversed this effect in a clinical
trial.6 People taking metformin should supplement vitamin B12 and folic acid or ask
their doctor to monitor folic acid and vitamin B12 levels.
In a study of patients with poorly controlled type
2 diabetes, low blood levels of magnesium, and high urine magnesium loss, metformin
therapy was associated with reduced urinary magnesium losses but no change in low blood levels
of magnesium.7 Whether this interaction has clinical importance remains
In a small, controlled study, guar gum plus metformin slowed the rate of metformin
absorption.8 In people with diabetes this interaction could reduce the blood
sugar–lowering effectiveness of metformin. Until more is known, metformin should be
taken two hours before or two hours after guar gum–containing supplements. It remains
unclear whether the small amounts of guar gum found in many processed foods is enough to
significantly affect metformin absorption.
Interactions with Herbs
In a preliminary trial, administration of Ginkgo biloba extract (120 mg per day) for
three months to patients with type 2 diabetes who were taking oral anti-diabetes medication
resulted in a significant worsening of glucose tolerance. Ginkgo did not impair glucose
tolerance in individuals whose diabetes was controlled by diet.9 Individuals taking
oral anti-diabetes medication should consult a doctor before taking Ginkgo
Interactions with Foods and Other Compounds
Food interferes with metformin absorption.10 11 12 Taking
metformin with food can reduce the absorption of the drug. Therefore, metformin should be
taken an hour before or two hours after a meal unless stomach upset occurs.
Lactic acidosis is a rare but serious side effect of metformin. Alcohol increases the
production of lactic acid caused by metformin, increasing the risk of lactic
acidosis.13 People taking metformin should avoid alcohol or consult with their
doctor before consuming alcohol.
1. Anderson RA, Cheng N, Bryden NA, Polansky MM, Cheng N, Chi J, et al.
Elevated intakes of supplemental chromium improve glucose and insulin variables in individuals
with type 2 diabetes. Diabetes 1997;46:1786–91.
2. Nestler JE, Beer NA, Jakubowicz DJ, Beer RM. Effects of a reduction in
circulating insulin by metformin on serum dehydroepiandrosterone sulfate in nondiabetic men.
J Clin Endocrinol Metab 1994;78:549–54.
3. Crave JC, Fimbel S, Lejeune H, et al. Effects of diet and metformin
administration on sex hormone-binding globulin, androgens, and insulin in hirsute and obese
women. J Clin Endocrinol Metab 1995;80:2057–62.
4. Carpentier JL, Bury J, Luyckx A, Lefebvre P. Vitamin B 12 and folic
acid serum levels in diabetics under various therapeutic regimens. Diabete Metab
5. Carlsen SM, Folling I, Grill V, et al. Metformin increases total serum
homocysteine levels in non-diabetic male patients with coronary heart disease. Scand J
Clin Lab Invest 1997;57:521–7.
6. Bauman WA, Shaw S, Jayatilleke E, et al. Increased intake of calcium
reverses vitamin B12 malabsorption induced by metformin. Diabetes Care
7. McBain AM, Brown IR, Menzies DG, Campbell IW. Effects of improved
glycaemic control on calcium and magnesium homeostasis in type II diabetes. J Clin
8. Gin H, Orgerie MB, Aubertin J. The influence of Guar gum on absorption
of metformin from the gut in healthy volunteers. Horm Metab Res
9. Kudolo GB. The effect of 3-month ingestion of Ginkgo biloba extract
(EGb 761) on pancreatic beta-cell function in response to glucose loading in individuals with
non-insulin-dependent diabetes mellitus. J Clin Pharmacol 2001;41:600–11.
10. Cardot JM, Saffar F, Aiache JM. Influence of food on glycemia,
insulin, C-peptide and glucagon levels in diabetic patients treated with antidiabetic
metformin at steady-state. Methods Find Exp Clin Pharmacol 1997;19:715–21.
11. Sambol NC, Brookes LG, Chiang J, et al. Food intake and dosage level,
but not tablet vs solution dosage form, affect the absorption of metformin HCl in man. Br
J Clin Pharmacol 1996;42:510–2.
12. Sifton DW, ed. Physicians Desk Reference, Montvale, NJ:
Medical Economics Co., Inc., 2000, 831–5.
13. Threlkeld DS, ed. Hormones, Antidiabetic Agents, Biguanides,
Metformin HCl. In Facts and Comparisons Drug Information. St. Louis, MO: Facts and
Comparisons, May 1995, 130n–130u.