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Metformin is a drug used to lower blood sugar levels in people with non-insulin-dependent (type 2) diabetes.
Common brand names:Fortamet, Glucophage, Glumetza, Riomet
Summary of Interactions with Vitamins, Herbs, & Foods
Replenish Depleted Nutrients
Metformin therapy has been shown to deplete vitamin B12,1 and sometimes, but not always,2 folic acid as well.3 This depletion occurs through the interruption of a calcium-dependent mechanism. People taking metformin should supplement vitamin B12 and folic acid or ask their doctor to monitor folic acid and vitamin B12 levels.
Metformin therapy has been shown to deplete vitamin B12,4 and sometimes, but not always,5 folic acid as well.6 People taking metformin should supplement vitamin B12 and folic acid or ask their doctor to monitor folic acid and vitamin B12 levels.The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
Reduce Side Effects
In a small, controlled study, guar gum plus metformin slowed the rate of metformin absorption.7 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.The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
Potential Negative Interaction
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.8 Individuals taking oral anti-diabetes medication should consult a doctor before taking Ginkgo biloba.
Chromium supplements have been shown to improve blood sugar control in people with diabetes.9 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 studies.10 , 11
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.12 Whether this interaction has clinical importance remains unclear.
1. de Jager J, Kooy A, Lehert P, et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ 2010;340:c2181.
2. Carpentier JL, Bury J, Luyckx A, Lefebvre P. Vitamin B 12 and folic acid serum levels in diabetics under various therapeutic regimens. Diabete Metab 1976;2:187-90.
3. 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.
4. de Jager J, Kooy A, Lehert P, et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ 2010;340:c2181.
5. Carpentier JL, Bury J, Luyckx A, Lefebvre P. Vitamin B 12 and folic acid serum levels in diabetics under various therapeutic regimens. Diabete Metab 1976;2:187-90.
6. 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.
7. Gin H, Orgerie MB, Aubertin J. The influence of Guar gum on absorption of metformin from the gut in healthy volunteers. Horm Metab Res 1989;21:81-3.
8. 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.
9. 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. Diabetes1997;46:1786-91.
10. 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.
11. 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.
12. McBain AM, Brown IR, Menzies DG, Campbell IW. Effects of improved glycaemic control on calcium and magnesium homeostasis in type II diabetes. J Clin Pathol 1988;41:933-5.
Last Review: 03-18-2015
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