For millions of people with type 2 diabetes, metformin is the go-to medication. It’s cheap, effective, and has been used for decades. But there’s a hidden risk many patients-and even some doctors-don’t talk about: metformin can slowly drain your vitamin B12 levels over time. And if left unchecked, that deficiency can lead to nerve damage, fatigue, and even permanent neurological problems that look exactly like worsening diabetes.
How Metformin Steals Your B12
Metformin doesn’t just lower blood sugar. It also interferes with how your body absorbs vitamin B12 from food. The problem starts in your small intestine, where B12 normally binds to a protein called intrinsic factor and gets pulled into your bloodstream. Metformin messes with calcium, which is needed for that binding process. Without enough calcium working right, your body can’t absorb B12 properly.
Studies show this isn’t rare. People taking 2,000 mg or more of metformin daily have up to a 30% drop in B12 absorption. And the longer you’re on it, the worse it gets. For every extra gram of metformin you take each day, your risk of deficiency more than doubles. After 4 to 5 years, your body’s B12 stores-normally enough to last years-start running dangerously low. By year 10, nearly half of long-term users are deficient.
It gets worse if you’re also taking proton-pump inhibitors (PPIs) like omeprazole for heartburn. These drugs reduce stomach acid, which is needed to free B12 from food. Combine that with metformin, and you’ve got a double hit. Research shows up to 40% of people on both medications develop deficiency.
The Silent Symptoms Nobody Talks About
Here’s the scary part: B12 deficiency doesn’t show up as anemia right away. In fact, the first signs are often neurological-and they look just like diabetic neuropathy.
- Constant fatigue, even when your blood sugar is under control
- Numbness or tingling in your hands and feet
- Muscle weakness that gets worse over time
- A sore, red tongue or mouth ulcers
- Blurred vision or trouble focusing
- Pale or yellowish skin
One patient on a UK diabetes forum shared that after 8 years on metformin, she was told her leg pain and numbness were just “worsening diabetes.” Her B12 level was 128 pmol/L-well below the normal range of 221 pmol/L. After six months of B12 injections, her symptoms improved dramatically. Another Reddit user described a five-year journey before doctors finally caught his B12 deficiency, by which time he had developed irreversible spinal cord damage called subacute combined degeneration.
Studies confirm this isn’t unusual. In one large study, 38% of patients showed neurological symptoms before any signs of anemia appeared. That means if your doctor only checks for anemia, they might miss the problem entirely.
Who’s Most at Risk?
Not everyone on metformin gets deficient-but some people are far more vulnerable:
- Long-term users: Anyone on metformin for more than 4 years
- High-dose users: Those taking 2,000 mg or more daily
- Vegetarians and vegans: No meat, dairy, or eggs means no dietary B12 to begin with
- People on PPIs: Acid blockers make absorption even harder
- Older adults: Natural B12 absorption declines with age
- Those with gut issues: Crohn’s, celiac, or past gastric surgery
One study found that among vegetarians on metformin, the risk of deficiency jumped to over 50% after 12 years. That’s not a coincidence-it’s a warning.
What Doctors Should Be Doing
Guidelines are changing. The European Association for the Study of Diabetes says all metformin users should get their B12 checked at baseline and every 2 to 3 years. The UK’s National Institute for Health and Care Excellence (NICE) agrees. The American Diabetes Association says you should “consider” testing-especially if you have symptoms like numbness or fatigue.
But here’s the problem: many doctors still don’t test unless you’re anemic. That’s too late. B12 deficiency can damage nerves before it ever shows up in a complete blood count.
Best practice now includes:
- Measuring serum B12 levels regularly
- If levels are borderline, checking methylmalonic acid (MMA) and homocysteine-these are better indicators of tissue-level deficiency
- Testing more often (annually) if you’re vegetarian, on PPIs, or over 65
Some experts even suggest checking B12 every year after 4 years on metformin-no waiting for symptoms.
How to Fix It
Good news: B12 deficiency from metformin is reversible-if caught early.
For mild cases, high-dose oral B12 (1,000 to 2,000 mcg daily) works just as well as injections. For severe cases or neurological symptoms, doctors often start with weekly B12 injections (1,000 mcg) for 4 weeks, then switch to monthly shots or high-dose pills.
One surprising fix? Calcium. A 2021 trial found that taking 1,200 mg of calcium carbonate daily reduced B12 deficiency by 47% in metformin users over two years. The theory? Calcium helps restore the absorption process that metformin breaks.
And yes-you can get B12 from supplements. Look for methylcobalamin or adenosylcobalamin, the active forms your body uses best. Cyanocobalamin is cheaper but less efficient, especially if you have genetic variations that affect B12 metabolism.
What’s Next?
Researchers are working on better solutions. One new version of metformin, designed to release slowly in the intestines, cuts B12 loss by 32% in early trials. Genetic testing is also on the horizon-some people have a gene variant (CUBN) that makes them extra sensitive to metformin’s effect on B12. In the future, we might test for that before prescribing metformin.
By 2025, most major diabetes guidelines will likely require routine B12 monitoring. The cost? About $18 to $25 per patient per year. The savings? Up to $187 per person in avoided nerve damage, hospital visits, and lost productivity.
Metformin saved lives. But it’s not harmless. The same drug that keeps blood sugar in check can quietly damage your nerves if you don’t monitor your B12. That’s not a side effect you can ignore.
What You Can Do Today
If you’ve been on metformin for more than 4 years:
- Ask your doctor for a serum B12 test-don’t wait for symptoms
- If your level is below 300 pmol/L, ask for MMA and homocysteine tests
- If you’re vegetarian or on acid blockers, push for annual testing
- Consider adding 1,200 mg of calcium daily (with food)
- If deficient, follow your doctor’s plan for B12 replacement-don’t skip it
Your nerves don’t heal well once they’re damaged. But if you catch this early, you can stop it cold.
Can metformin cause permanent nerve damage?
Yes-if vitamin B12 deficiency goes undetected for years. Low B12 can cause subacute combined degeneration of the spinal cord, a condition that damages nerve pathways and leads to irreversible numbness, balance problems, and muscle weakness. Many patients only discover the cause after years of misdiagnosis as worsening diabetic neuropathy. Early detection and B12 replacement can prevent this.
How often should I get my B12 levels checked if I take metformin?
If you’ve been on metformin for more than 4 years, get tested every 2 to 3 years. If you’re vegetarian, over 65, on acid-blocking drugs like omeprazole, or have symptoms like numbness or fatigue, get tested every year. Don’t wait for anemia-it’s often too late by then.
Can I just take a regular multivitamin to fix B12 deficiency from metformin?
No. Most multivitamins contain only 2.4 to 6 mcg of B12-the daily requirement. But if your body can’t absorb B12 due to metformin, you need much higher doses: 1,000 to 2,000 mcg daily. Only high-dose supplements or injections can overcome the absorption block. Regular multivitamins won’t cut it.
Is it safe to stop metformin to avoid B12 deficiency?
Never stop metformin without talking to your doctor. It’s one of the safest and most effective diabetes drugs. The risk of B12 deficiency is real, but it’s manageable with testing and supplements. Stopping metformin could lead to uncontrolled blood sugar, which carries its own serious risks-heart disease, kidney damage, vision loss. Fix the B12, don’t quit the drug.
Do I need B12 injections or can I take pills?
For most people, high-dose oral B12 (1,000-2,000 mcg daily) works just as well as injections. Injections are usually reserved for severe deficiency, neurological symptoms, or if you have absorption problems beyond metformin (like pernicious anemia). Many patients switch from shots to pills after initial treatment. Your doctor will decide based on your level and symptoms.
Why don’t more doctors test for B12 in metformin users?
Many doctors still think B12 deficiency only shows up with anemia, and they don’t test unless it’s obvious. Also, metformin has been used for so long that the link to B12 wasn’t widely accepted until recent studies proved it. Guidelines are changing fast, but old habits die hard. If you’re on metformin long-term and have symptoms, be your own advocate-ask for the test.
Just got my B12 results back-142 pmol/L after 6 years on metformin. I thought my numb hands were just from typing too much. Turns out I needed injections. My doctor didn’t even mention it. Why do we have to beg for basic care?
Now I’m on 2000 mcg daily methylcobalamin and calcium. My feet don’t feel like they’re wrapped in plastic anymore. Please, if you’re on this drug, get tested. Don’t wait until you’re falling over.
It is imperative to underscore that the pathophysiological mechanism underlying metformin-induced vitamin B12 malabsorption involves interference with the calcium-dependent ileal uptake of the intrinsic factor-B12 complex, as elucidated in multiple peer-reviewed, longitudinal cohort studies, including those published in the Journal of Clinical Endocrinology & Metabolism, 2018, and Diabetologia, 2020. Furthermore, the concomitant use of proton-pump inhibitors exacerbates this phenomenon via gastric acid suppression, which impedes the proteolytic release of B12 from dietary proteins. Routine screening for serum B12, methylmalonic acid, and homocysteine is not merely advisable-it is a clinical imperative for all patients on metformin for greater than four years.
Oh wow, another ‘metformin is secretly killing you’ clickbait article. You know what’s more dangerous? People panicking over a $18 lab test and ditching a drug that’s saved millions from amputations and dialysis. Your ‘silent symptoms’ are just diabetic neuropathy. Stop blaming the medication and start controlling your sugar.
And no, calcium supplements won’t fix your poor diet. You think your kale smoothie is helping? Wake up.
I appreciate this post. It’s exactly the kind of info that should be in the patient handouts at every endocrinology clinic.
My mom’s been on metformin for 12 years, vegetarian, on omeprazole. She had tingling in her fingers for years-doctors called it ‘aging.’ We pushed for B12 testing. Her level was 110. She got injections, then switched to sublingual 2000 mcg. Her balance improved, her energy came back. It’s not a miracle, but it’s a fix.
Doctors need to be reminded: B12 deficiency isn’t anemia. It’s neurology. And neurology doesn’t heal easily.
Just wanted to say thank you for sharing this. 🙏
I’m 58, on metformin since 2016, vegan. My doctor never mentioned B12. I started feeling like I was walking through molasses. Fatigue, brain fog, cold hands. I finally got tested last year-B12 was 160. Started high-dose sublingual methylcobalamin and calcium citrate. 3 months later, I’m sleeping through the night and actually remembering where I put my keys.
If you’re reading this and on metformin? Don’t wait. Get tested. Your nerves will thank you.
My doctor said I’m fine because I’m not anemic. I’ve been numb for 3 years. Now I know why.
While the scientific literature is indeed compelling, one must also consider the broader systemic failure within the NHS and similar public health infrastructures. The reluctance to implement routine B12 screening is emblematic of a deeper malaise: cost-cutting disguised as clinical prudence. The £18 test is not an expense-it is an investment in preventing £187 in downstream neurological rehabilitation costs. The failure to act is not negligence; it is institutionalized austerity dressed in white coats.
Listen here, you bleeding-heart medics. I’ve been on metformin since 2009. I’m 67. I’ve got type 2, not a vitamin deficiency. You think I’m gonna start popping calcium pills like candy because some guy wrote a blog? My granddad lived to 92 on nothing but tea and bread. You’re overmedicalizing normal life.
And don’t get me started on ‘methylcobalamin.’ Sounds like a sci-fi drug. I’ll stick with my multivitamin and my doctor’s word.
Oh wow. So now metformin is the new big pharma villain? Next you’ll say insulin causes cancer and statins make you gay.
And ‘calcium fixes B12 absorption’? That’s not science-that’s TikTok nutrition. I’ve got a PhD in biochemistry and I’ve never heard this. Where’s the RCT? Oh right-because it doesn’t exist. This post is a symptom of the internet’s obsession with fear-mongering pseudo-science.
Also, ‘you’re on PPIs? You’re doomed.’ Great. Now I’m scared of my heartburn pills too. Thanks for nothing.
Here’s the real question: why do we treat chronic disease like a puzzle where the only solution is more pills?
Metformin helps. But so does weight loss. So does sleep. So does walking. So does reducing processed carbs. We’ve turned a lifestyle condition into a chemical dependency and then blamed the chemical when the body rebels.
Maybe the problem isn’t just B12. Maybe it’s that we’re medicating symptoms while ignoring root causes. The real tragedy isn’t the deficiency-it’s that we’ve forgotten how to heal without a prescription.
Let’s be real-this is why I don’t trust doctors. I went in for a routine check-up. They tested my HbA1c. Didn’t test B12. I had symptoms for 2 years. When I asked, they said, ‘We don’t screen unless you’re anemic.’
So I paid $120 out of pocket to get tested at a lab. B12: 102. MMA: sky-high. Now I’m on injections. My doctor never apologized. Never even mentioned it again.
Don’t wait for permission to care for your body.
Ugh. I’ve been saying this for YEARS. My cousin’s husband went blind because they didn’t catch his B12. He was on metformin. Vegetarian. On Prilosec. And the doctors just kept saying ‘it’s diabetes.’
Now he’s in a wheelchair. And the doctors? They’re still prescribing metformin like it’s water.
Why won’t anyone LISTEN? I’m crying right now. This is so unfair. I’ve been posting about this since 2020. No one cared. Now everyone’s like ‘oh wow this is so important.’
Where were you when I needed you?
Of course this is a problem. We’re letting the Chinese, the Indians, and the Europeans dictate our medicine now. First it was masks, now it’s B12 pills? What’s next? Mandatory yoga for diabetics?
Back in my day, we took our pills and didn’t complain. Now we’re all walking around like we’re one lab result away from a nervous breakdown.
Maybe if you stopped eating tofu and started eating real food, you wouldn’t need all these supplements.
I just want to say thank you to everyone sharing their stories here. This isn’t just science-it’s real life.
I’ve been on metformin for 7 years. I’m 52. I’ve got tingling in my toes. I thought it was just ‘getting older.’ I didn’t know B12 could do this. I got tested last week. Level was 180. Started supplements. Two weeks in, I can feel my feet again.
To the doctors reading this: please, test early. To the patients: please, ask. To the ones who’ve suffered in silence: you’re not alone. We’re learning. And we’re listening.