Metformin may already be part of your PCOS care plan. Alongside conversations about how it is working and how you are feeling, there is one small question worth adding: “When should we check my vitamin B12?”

Metformin can lower B12 levels in some people. That does not mean everyone taking it becomes deficient, or that you should stop a helpful prescription. It means B12 deserves a place in your follow-up care. [1–3]

Why B12 matters

Vitamin B12 helps maintain healthy nerves and red blood cells. Metformin can interfere with B12 absorption, even when your diet includes B12-containing foods. [3]

The international PCOS guideline specifically flags low B12 as a possible issue during metformin use and advises considering monitoring, particularly when other risk factors are present. This is a medication-related consideration, not proof that everyone with PCOS has a B12 deficiency. [1]

Who should bring it up?

Risk can increase with a higher metformin dose or longer treatment. Your clinician also needs to know about previous low B12, stomach or intestinal conditions that affect absorption, bariatric surgery, and medicines that reduce stomach acid. [1,2]

Vegan and some vegetarian eating patterns can mean fewer dietary sources of B12. Reliable fortified foods or an appropriate supplement plan can help meet intake needs; this is a reason to plan, not a reason to abandon an eating pattern that works for you. [2,3]

Symptoms are clues, not a diagnosis

New or worsening unusual tiredness, a sore red tongue, or tingling and numbness deserve a conversation with your clinician. These symptoms can have many causes. Do not automatically attribute them to PCOS, metformin, or a vitamin deficiency. [2]

B12-related nerve problems can occur without anemia. A normal blood count alone therefore does not settle the question when symptoms suggest a problem. [3]

When should B12 be tested?

There is useful guidance to start the conversation. U.S. prescribing information for metformin tablets includes annual blood-count monitoring and B12 measurement every two to three years. The PCOS guideline emphasizes considering B12 monitoring in those at increased risk. [1,4]

Your own schedule may need to be sooner because of symptoms, previous results, diet, other medicines, or absorption problems. Ask your prescriber what applies to your particular prescription and medical history.

If an initial B12 result is borderline or does not fit the clinical picture, your clinician may consider another marker, methylmalonic acid (MMA). Kidney function can affect MMA, so it also needs context. [3]

What does the research actually show?

Long-term trials in people with type 2 diabetes support the link between metformin and lower B12. Those results do not give us an exact deficiency rate for people taking it for PCOS. [5]

PCOS-specific research also deserves nuance. A small study found lower total B12 during metformin treatment without corresponding changes in two other B12-status markers over up to six months. A lower laboratory number is not always equivalent to symptomatic deficiency. Equally, a small short study cannot establish long-term safety without monitoring. [6]

What if your level is low?

Your clinician can identify the likely cause and choose treatment when needed. B12 deficiency can often be addressed while metformin continues; do not change the prescription on your own. [2]

Taking a multivitamin does not establish that your B12 status is adequate or that a diagnosed deficiency is being treated appropriately. Dietary intake, absorption, test results, and symptoms all matter. [3]

For your next appointment, save these questions:

• When was my B12 last checked, and when should it be checked again?
• Do my diet, medicines, or medical history increase my risk?
• Do any new symptoms need evaluation now?

A good PCOS care plan includes follow-up. Asking about B12 is one practical way to make that follow-up more complete.

Related reading: Insulin Resistance in PCOS/PMOS: Signs, Tests, and What Your Results Mean.

Considering a daily multivitamin?

For adults comparing options for general dietary supplementation, WrenLife GLP-1 Support Multi+ is an iron-free multivitamin that lists 25 mcg of B12 as methylcobalamin per two-tablet serving. It may be relevant when food intake is reduced, including during GLP-1 medication use. Review the complete formula with your clinician to decide whether it fits your needs. It should not replace B12 monitoring or individualized deficiency treatment. [7]

Before bloodwork: Multi+ contains 3,000 mcg of biotin per serving, which can interfere with certain laboratory tests. Tell your clinician and laboratory about all supplements you use and follow their test-specific instructions. [7]

View Multi+ ingredients and safety information.

Educational information, not individualized medical advice. WrenLife sells dietary supplements; this article does not recommend a WrenLife product as treatment for B12 deficiency or PCOS.

References

1. Teede HJ, Tay CT, Laven JJE, et al. Recommendations From the 2023 International Evidence-Based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Journal of Clinical Endocrinology & Metabolism. 2023;108:2447–2469. Practice point 4.3.4. Guideline via ASRM.

2. Medicines and Healthcare products Regulatory Agency. Metformin and reduced vitamin B12 levels: new advice for monitoring patients at risk. Drug Safety Update. 2022. MHRA guidance.

3. National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. NIH fact sheet.

4. DailyMed. Metformin hydrochloride tablets: U.S. prescribing information, section 5.2, Vitamin B12 Deficiency. Current label reviewed.

5. de Jager J, et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ. 2010;340:c2181. Study.

6. Greibe E, Trolle B, Bor MV, Lauszus FF, Nexo E. Metformin lowers serum cobalamin without changing other markers of cobalamin status: a study on women with polycystic ovary syndrome. Nutrients. 2013;5:2475–2482. Study.

7. WrenLife. GLP-1 Support Multi+: current product information and Supplement Facts, two-tablet serving. Product label and safety information.