Based on NIH | Can metformin cause numbness or tingling in the hands and feet, and could this be due to vitamin B12 deficiency?

Yes metformin can contribute to numbness or tingling (paresthesia) in the hands and feet, and one plausible mechanism is vitamin B12 deficiency that develops during long‑term use. In clinical trials, metformin has been associated with a drop to below‑normal serum vitamin B12 levels in a portion of users, likely due to reduced absorption of the B12–intrinsic factor complex. ^[1] This reduction is usually reversible with either stopping metformin or supplementing vitamin B12, and routine monitoring of blood counts yearly and B12 every 2–3 years is commonly advised for people on ongoing therapy. ^{[2] [3]}

How metformin relates to B12 and nerve symptoms

• Metformin can lower vitamin B12 levels over time in some people by interfering with gut absorption. ^[1] This effect can occur without obvious anemia, so deficiency may be missed unless specifically checked. ^[2]
• Guidance commonly recommends checking hematologic parameters annually and considering periodic B12 testing (about every 2–3 years), especially if intake or absorption is borderline. ^{[4] [5]}
• When deficiency is present, it may cause nerve damage symptoms such as numbness, tingling, burning, or weakness; these symptoms can overlap with diabetic neuropathy, making clinical recognition important. ^[6] B12 repletion can halt progression, and earlier treatment offers a better chance of symptom improvement. ^[7]

What the research shows

• Observational data and clinical reports link metformin exposure with lower B12 levels, higher odds of B12 deficiency, and higher neuropathy scores, with a stronger association at higher cumulative doses. ^[6]
• Case reports describe peripheral neuropathy from metformin‑induced B12 deficiency that can be misattributed to diabetes unless B12 is tested, emphasizing the need for screening. ^[7]

Other causes of numbness and tingling to consider

While B12 deficiency is one explanation, there are several other common causes of peripheral neuropathy, including long‑standing diabetes itself, kidney problems, certain infections, autoimmune diseases, toxin exposure, some medicines (for example, chemotherapy), and mechanical nerve injury. ^{[8] [9]} A careful evaluation helps distinguish among these possibilities and guide the right treatment. ^[10]

What you can do now

• If you take metformin and have persistent numbness or tingling, it’s reasonable to ask for a vitamin B12 blood test, and if borderline, to add methylmalonic acid or homocysteine to assess tissue‑level deficiency. Testing is especially pertinent if you’ve been on metformin for years, take higher doses, or follow a diet low in animal products. ^[4]
• If B12 is low, doctors typically recommend B12 supplementation and reassessment; neurologic symptoms may improve and progression can be prevented, although recovery can vary depending on duration. ^[2]
• Continuing metformin is often possible with B12 supplementation and periodic monitoring, unless there are other reasons to change therapy. Many users remain on metformin safely with appropriate B12 surveillance. ^[11]

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Quick reference: Metformin, B12, and neuropathy

Topic	Key points
Can metformin lower B12?	Yes; metformin can reduce B12 absorption, and some users develop below‑normal B12. [1]
How common?	Subnormal B12 levels occurred in a subset of users in controlled trials; risk rises with cumulative exposure and individual predisposition. [1] [6]
Symptoms to watch	Numbness, tingling, burning, weakness, balance issues; these can mimic diabetic neuropathy. [6]
Monitoring	Check blood counts yearly and consider B12 every 2–3 years; sooner if symptoms or risk factors. [4] [5]
Reversibility	B12 levels and related findings often improve with supplementation or stopping metformin. [2]

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Bottom line

Metformin use can be associated with vitamin B12 deficiency, which in turn may cause numbness or tingling in the hands and feet; testing and treating B12 deficiency can help prevent nerve damage and may improve symptoms while allowing many people to continue metformin safely. ^{[1] [2] [6]}