Vitamin B12 and your other medications

Why the direction of the interaction matters

Vitamin B12 is water-soluble, and the NIH Office of Dietary Supplements notes it has no Tolerable Upper Intake Level because it's considered safe even at high intakes. So the usual worry, that a supplement might change how your prescriptions work, isn't the main concern with B12.

The concern is the reverse. To absorb B12 from food, you need stomach acid to free it from protein and a protein called intrinsic factor to carry it into the bloodstream. Medicines and conditions that interfere with either step can, over months to years, leave you short.

Metformin

Metformin is a first-line medicine for type 2 diabetes and is also used for prediabetes. According to the NIH fact sheet, it may reduce B12 absorption and significantly lower blood B12 levels. MedlinePlus lists long-term metformin use among the causes of B12 deficiency anemia.

This builds slowly, so it's most relevant if you've been on metformin for years. It's also easy to miss, because B12 deficiency can cause numbness and tingling in the hands and feet, which people with diabetes may assume is diabetic nerve damage. If you take metformin, periodic B12 checks are a reasonable thing to ask about. Don't stop metformin on your own.

Acid reducers for heartburn and reflux

Proton pump inhibitors such as omeprazole and lansoprazole, and H2 blockers such as famotidine and cimetidine, reduce stomach acid. With less acid, less B12 is released from food. The NIH fact sheet names both classes as medicines that can interfere with absorption and potentially lead to deficiency, and MedlinePlus lists long-term use of heartburn medicines as a cause.

Many people start these drugs for a short course and stay on them for years. If that's you, it's worth reviewing whether you still need them and whether your B12 has been checked.

Nitrous oxide

Nitrous oxide, or laughing gas, inactivates B12 in the body rather than blocking absorption. MedlinePlus lists nitrous oxide abuse as a cause of B12 deficiency anemia. Recreational use, sometimes heavy and repeated, has become a recognized cause of serious B12-related nerve injury.

If you've used nitrous oxide recreationally or have had it for medical or dental procedures and have numbness, tingling or balance problems, tell your clinician.

The folic acid trap

B12 deficiency can cause a type of anemia with large red blood cells. Folate (or folic acid) can correct that anemia, but it doesn't fix the nerve damage B12 deficiency causes. The NIH folate fact sheet explains that this is why experts worried high folic acid intake could hide B12 deficiency until neurological damage became permanent, and why the adult upper limit for folic acid from supplements and fortified foods is 1,000 mcg a day.

In practice: a normal blood count doesn't rule out B12 deficiency, especially if you take folic acid. When the picture is unclear, clinicians may check methylmalonic acid (MMA), which the NIH describes as the most sensitive marker of B12 status.

Biotin and your lab results

B12 is often sold alongside biotin in 'energy' and hair products. High-dose biotin can distort some lab tests, including thyroid tests, producing falsely high or low results. The NIH biotin fact sheet describes an FDA report of a falsely low troponin test in a patient taking high-dose biotin. Mention any biotin you take, and ask whether to pause it before blood work.

What to tell your clinician

• How long you've taken metformin or acid-reducing medicine.
• Any weight-loss or stomach surgery, or digestive conditions such as Crohn's or celiac disease.
• Recreational or recent medical nitrous oxide exposure.
• All supplements, especially folic acid and biotin.
• Symptoms such as numbness, tingling, balance problems, memory changes or unusual fatigue.

Signs that B12 may be running low

B12 deficiency develops slowly, and early signs are easy to blame on age or stress. MedlinePlus lists fatigue, pale skin and shortness of breath from anemia, and nerve symptoms such as numbness and tingling in the hands and feet, balance problems, trouble concentrating and irritability. In severe or long-standing cases, it can affect memory and mood.

Nerve damage from B12 deficiency can become permanent if it's left untreated for a long time, which is why it's worth checking sooner rather than later if you're in a higher-risk group, such as long-term metformin or acid-reducer users, adults with past stomach or bowel surgery, and people who eat no animal products.

How HealifyMD can help

Your clinician can review your medications, order labs (the comprehensive lab panel is listed at $199) and, when appropriate, prescribe B12 Injection, listed from $125/month. Injections bypass the gut, which is why they're used when absorption is the problem. Prices are confirmed at your eligibility review.