Metformin and B12 Deficiency: What You Need to Know

When you take metformin, a common medication for type 2 diabetes that helps lower blood sugar by reducing liver glucose production and improving insulin sensitivity. It's one of the most prescribed drugs in the world—but it doesn’t come without hidden side effects. One of the least talked about? vitamin B12 deficiency, a condition where your body lacks enough of this essential nutrient to make healthy red blood cells and maintain nerve function. Studies show that up to 30% of people on long-term metformin develop low B12 levels, even if they eat plenty of meat, eggs, or dairy. It’s not a myth. It’s science.

Why does this happen? Metformin interferes with how your small intestine absorbs B12, especially when calcium isn’t available to help with the process. Over time, your stores drain. You might not feel anything at first. But then comes the fatigue that won’t quit, tingling in your hands or feet, trouble remembering things, or even mood changes that feel like depression. These aren’t just "getting older" symptoms—they could be your body screaming for B12. And if left unchecked, low B12 can cause nerve damage that’s hard to reverse.

Who’s most at risk? People who’ve been on metformin for more than 4 years, older adults, vegetarians, and those already dealing with gut issues like Crohn’s or celiac disease. If you’re on metformin and you’re tired all the time, or your doctor says your blood work looks "fine" but you still don’t feel right—ask for a vitamin B12 blood test, a simple lab check that measures your serum B12 levels and sometimes methylmalonic acid or homocysteine for more accuracy. Don’t wait for symptoms to get worse. Some doctors check B12 yearly for metformin users. Others don’t. You might need to push for it.

Fixing it isn’t complicated. Oral B12 supplements work for most people, even with absorption issues. High-dose sublingual tablets or injections are options if your levels are really low. You don’t need to stop metformin—just add B12. And if you’re taking other meds like proton pump inhibitors for acid reflux, that can make things worse. It’s not just one drug. It’s the combo.

The posts below aren’t just about metformin or B12 alone. They connect the dots between medication, diet, absorption, and long-term health. You’ll find real advice on how to spot hidden side effects, what to ask your doctor, how supplements interact with prescriptions, and how to protect yourself when you’re on multiple drugs. This isn’t theory. It’s what people actually deal with every day. And you’re not alone in it.