Metformin is one of the most widely used and trusted diabetes medications. It's also linked to lower vitamin B12 levels with long-term use. That doesn't mean anyone should stop taking it. It does mean B12 is worth keeping an eye on.
Written by Vita Globe Editorial Team | Reviewed against American Diabetes Association guidance, NIH guidance and peer-reviewed research
Does metformin cause B12 deficiency?
Long-term metformin use is associated with lower B12 levels and a higher risk of deficiency. In the Diabetes Prevention Program Outcomes Study, long-term metformin use was linked to biochemical B12 deficiency, and the risk increased with longer use[1]. The American Diabetes Association recommends periodic B12 testing in people taking metformin long term, especially those with neuropathy or anemia[2].
Caveat: Never stop or change metformin without your prescriber. The answer to low B12 is testing and, if needed, treatment, not stopping a medication that works.
Sources: Aroda et al., 2016 · ADA Standards of Care 2025 · NIH ODS · Verified 2026-09-27
IN THIS ARTICLE
How does metformin lower B12?
The NIH notes that metformin might reduce the absorption of B12 and can significantly reduce blood B12 levels[3]. The exact mechanism isn't fully understood. What is clear is that the effect builds over time, which is why it tends to show up after years of use rather than weeks.
What does the research show?
The strongest evidence comes from the Diabetes Prevention Program Outcomes Study, which followed people originally randomized to metformin or placebo for many years. Long-term metformin use was associated with biochemical B12 deficiency, and the risk rose with total years of use[1].
These findings are why B12 monitoring is now part of diabetes care guidance[2].
Why does low B12 matter for people with diabetes?
B12 deficiency can damage nerves, causing numbness, tingling or burning in the feet and hands[4]. That overlaps with diabetic neuropathy, so a B12 problem can be missed or mistaken for diabetes complications. The ADA notes that B12 deficiency should be considered in people on metformin, particularly those with peripheral neuropathy[2].
Low B12 can also cause anemia and fatigue. For a full symptom list, see Vitamin B12 Deficiency: Signs, Causes, and What Actually Helps.
What should you do if you take metformin?
- Ask about testing. The ADA recommends periodic B12 measurement with long-term metformin use[2], and NICE lists metformin among the medicines that can contribute to deficiency[5].
- Mention symptoms like tingling, numbness, balance problems or unusual tiredness.
- Tell your provider about all supplements so test results can be read correctly.
- If you take acid reducers too, mention it. Long-term PPI and H2 blocker use has also been linked to B12 deficiency[6].
If your provider recommends B12, they'll suggest a dose and route. For many people, high-dose oral B12 can raise levels; for others, injections are the better option. See B12 Shots vs. Gummies
The honest summary
- Long-term metformin use is linked to lower B12 and a higher risk of deficiency.
- Low B12 can cause nerve symptoms that overlap with diabetic neuropathy.
- Guidelines recommend periodic B12 testing for people on metformin.
- Keep taking your medication as prescribed and talk to your provider about B12.
Our option
Vita Globe Vitamin B12 Gummies for Adults
If your provider suggests adding B12, our B12 Gummies for Adults provide 1,000mcg of vitamin B12 (as cyanocobalamin) per two-gummy serving. Note that these gummies are not sugar-free, so if you are managing blood sugar, check the Supplement Facts panel and talk to your care team. B12 supports red blood cell formation and nervous system health.*
Frequently asked questions
How long does it take metformin to lower B12?
Changes usually build over years of use rather than weeks, and the risk rises with longer use[1].
Should everyone on metformin take B12?
Guidelines recommend periodic testing rather than automatic supplements for everyone[2]. Your provider will decide based on your levels and symptoms.
Can B12 deficiency from metformin cause neuropathy?
B12 deficiency can cause nerve damage, and it can look similar to diabetic neuropathy, which is why testing matters[2][4].
Does metformin affect other vitamins?
B12 is the vitamin most clearly linked to metformin in research[3]. Ask your provider about your specific situation.
Sources
- Aroda VR, et al. Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2016;101(4):1754-1761. doi:10.1210/jc.2015-3754
- American Diabetes Association Professional Practice Committee. 9. Pharmacologic approaches to glycemic treatment: Standards of Care in Diabetes—2025. Diabetes Care. 2025;48(Suppl 1):S181. doi:10.2337/dc25-S009
- Office of Dietary Supplements, National Institutes of Health. Vitamin B12: Fact Sheet for Health Professionals. Updated July 2, 2025. ods.od.nih.gov
- Stabler SP. Vitamin B12 deficiency. N Engl J Med. 2013;368(2):149-160. doi:10.1056/NEJMcp1113996
- National Institute for Health and Care Excellence. Vitamin B12 deficiency in over 16s: diagnosis and management (NICE guideline NG239). 2024. nice.org.uk/guidance/ng239
- Lam JR, Schneider JL, Zhao W, Corley DA. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA. 2013;310(22):2435-2442. doi:10.1001/jama.2013.280490
About the Vita Globe Editorial Team
The Vita Globe Editorial Team researches and writes our wellness content, working from peer-reviewed research, systematic reviews and guidance from bodies such as the NIH and the FDA. We cite our sources inline and update articles when the evidence changes.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for medical advice. Talk to your healthcare provider before starting any new supplement, particularly if you are pregnant, nursing, taking medication, or caring for a child.
