Vitamin B12 and medications.
Vitamin B12 is in the Distil supplement database, evidence Grade A. The page below lists every medication we have explicitly assessed it against.
Vitamin B12 supports nerve function, DNA synthesis, red blood cell production, and energy metabolism, and a shortfall shows up neurologically as well as in anaemia. The methylcobalamin form is the active one and is generally preferred, especially for nerve health, with a usual dose of 500 to 1,000mcg. Some groups need it more than others: vegans and vegetarians get essentially none from plant foods, absorption declines with age so sublingual forms suit the over-60s, and two common medicines deplete it. Metformin lowers B12 over time, so long-term users should supplement, and proton pump inhibitors such as omeprazole and lansoprazole reduce its absorption. It pairs with folate and TMG in the methylation cycle, and the evidence base includes trials on diabetic nerve conduction and brain health. It is extremely well tolerated, with any excess simply passed in urine. If you take metformin or a PPI long term, checking your level rather than assuming you are fine is the sensible move.
Below are the 7 documented pairs we have explicitly assessed for Vitamin B12: 7 amber. The pairs cluster around 1 mechanism: Absorption interference. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not listed here is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by medication, and the missing-item form at the bottom of the page routes any uncatalogued medication into our next curation pass.
Documented interactions
Absorption interference
Long-term colchicine can reduce how well your gut absorbs vitamin B12. It does this by temporarily damaging the lining of the lower small intestine, where B12 is taken up. The effect is linked to higher doses and longer courses, and it reverses once colchicine is stopped. Short courses for a gout flare are not a concern. If you are on colchicine long term, it is worth asking your GP about a B12 blood test.
Long-term esomeprazole use reduces stomach acid and slows how well your body absorbs vitamin B12 from food. After about two years of daily use, B12 deficiency becomes notably more likely. Good to know: a B12 supplement gets around this, because supplement B12 does not need stomach acid to be absorbed. If you take esomeprazole long term, ask your GP about an annual B12 blood test.
Long-term famotidine reduces stomach acid, which slows how well your body pulls vitamin B12 out of food. The effect is smaller than with stronger acid blockers like omeprazole, and it only matters after a couple of years of daily use. Good to know: a B12 supplement gets around this entirely, because supplement B12 does not need stomach acid to be absorbed. If you take famotidine daily for years, it is worth asking your GP for a B12 blood test.
Long-term lansoprazole use reduces stomach acid and slows how well your body absorbs vitamin B12 from food. After about two years of daily use, B12 deficiency becomes notably more likely. If you take lansoprazole long term, ask your GP about an annual B12 blood test.
Long-term metformin reduces vitamin B12 absorption in 10 to 30 percent of patients. After a year or more of daily use, ask your GP about an annual B12 blood test. Supplemental B12 (1000 mcg cyanocobalamin daily, or higher doses less frequently) reverses the deficiency in most people.
Long-term omeprazole use reduces stomach acid and slows how well your body absorbs vitamin B12 from food. After about two years of daily use, B12 deficiency becomes notably more likely. If you take omeprazole long term, ask your GP about an annual B12 blood test.
Long-term pantoprazole use reduces stomach acid and slows how well your body absorbs vitamin B12 from food. After about two years of daily use, B12 deficiency becomes notably more likely. Good to know: a B12 supplement gets around this, because supplement B12 does not need stomach acid to be absorbed. If you take pantoprazole long term, ask your GP about an annual B12 blood test.
What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope. Use the checker below to surface any medication, and submit a missing item if you take something we have not catalogued.
How we grade severity, choose what's in scope, and what we exclude.
Every call on this page is reasoned. We publish the full rubric for severity tiers, the medication inclusion logic, the evidence grades we accept, and what we deliberately leave out. About three thousand words. Worth reading once if you use this tool more than occasionally.
Read the full methodologyWant this checked across everything you take?
This page checks the pairs you enter. The personalised Distil report goes further:
- the same graded, cited interaction check across your whole stack, not just the pairs you thought to type in
- where your current routine may be leaving you short of your goals
- the evidence-backed compounds worth adding, and the ones worth dropping
It's a paid report: £79, or £49 for the first 25 customers. The interactions check is one section of it, and you can read a real one in full before you buy.
See a real sample reportSomething missing?
If a supplement or medication you take isn't in our autocomplete, tell us. We go through what people flag every week and add what's missing.