B12 on metformin
A short guided check: when to discuss testing, how to read your level, and what clinicians usually ask about B12 form.
Start
- Does not prescribe treatment
- Does not claim metformin causes neuropathy at population level
- MUI is a discussion trigger, not self-diagnosis
Your metformin exposure
We use this to estimate cumulative exposure (MUI). Count continuous years only.
MUI: —
Any of these right now?
Check all that apply — or choose none.
Stomach or bowel surgery
Had stomach or bowel resection? After gastrectomy — including for cancer — B12 deficiency is common. Discuss screening with your clinician.
Other risk factors
Vegan diet without B12, daily PPI use, or age 65+?
Discuss B12 testing
Worth discussing B12 with your clinician
Based on your answers, screening may make sense earlier than a “wait and see” approach.
First step: serum B12. MMA, HoloTC, and treatment decisions belong with your clinician.
Routine window (ADA)
Periodic screening is usually after ~4–5 years
You reported under 4 years on metformin, MUI ≤ 5, and no other triggers. ADA usually considers periodic B12 assessment after ~4–5 years of continuous use. Still ask your clinician when to schedule a first test if you are unsure.
Your serum B12 (pg/mL)
Pick the range that matches your lab report.
Select your B12 range above before answering this.
Chronic kidney disease?
Low / deficient B12
Discuss repletion with your clinician
With confirmed deficiency or a level below 200 pg/mL, clinicians often discuss 1000 mcg/day oral cyanocobalamin or methylcobalamin. Do not stop metformin on your own. Recheck in about three months per your clinician’s plan.
After stomach or bowel resection, oral repletion may not be enough — discuss IM B12 with your clinician.
Borderline level
200–300 pg/mL — often needs more labs
Borderline B12. MMA and/or HoloTC often help, especially with symptoms. Your clinician decides — not this guide.
With CKD, interpret MMA cautiously — false positives are possible.
Likely normal
Repeat on your clinician’s schedule
Above 300 pg/mL is likely normal on many assays. Repeat per your clinician’s plan; do not delay if new symptoms appear (anemia, numbness, dyspepsia).
B12 form
Dose beats form
- Cyanocobalamin and methylcobalamin at 1000 mcg/day are both acceptable if your clinician agrees.
- Methyl “for neuropathy” on the label is usually marketing — superiority is not established.
- Sublingual is optional; a swallowed tablet is often enough.
- IM B12 only per your clinician: oral failure, severe malabsorption, GI resection, or symptoms despite normalized labs.
What this covers
- Screening — years on metformin, MUI, symptoms, GI surgery, vegan/PPI/age 65+.
- Labs — serum B12 bands and when borderline results need MMA or HoloTC.
- Form — dose beats form; IM only per your clinician.
What this does not do
No diagnosis, no treatment orders, no metformin stop/start. Urgent neurologic symptoms belong in the ER or urgent care — not this tool.