Health Reference LibraryHow much vitamin B12 should I take, and can you take too much?
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
The right amount depends on why you are taking it. On a plant based diet, 10 micrograms a day or 2000 micrograms once a week keeps levels up. For a confirmed low result, the trials used 1000 to 2000 micrograms a day by mouth, and NICE accepts that route for suitable people at a dose the GP sets. The reference intake is only 1.5 micrograms, and the NHS says 2000 micrograms a day from supplements is unlikely to cause harm; there is no known toxic dose because the excess leaves in urine. The mistake to avoid is not overdosing but skipping the test that finds the cause of a low result.
Dose calculator: capsules to reach your vitamin B12 target
Enter the daily amount of vitamin B12 you are aiming for and see how many servings of each Nutri Tailor product reach it. Nothing you enter leaves this device. No AI is used.
This tool does arithmetic on the label figures. It is not personal dosing advice and it knows nothing about your history or blood results. The reference intake, the safe upper guide and the trial doses are on this page; talk to your GP or a registered nutritional therapist before changing what you take.
Effective dose
The reference intake is 1.5 micrograms a day for adults, easily met by meat, fish, eggs and dairy. It depends on why. For a plant based diet, 10 micrograms a day or 2000 micrograms once a week keeps levels up, because absorption through the intrinsic factor route saturates at a few micrograms and a large weekly dose gets in by simple diffusion. For a confirmed low result the trials used 1000 to 2000 micrograms a day, and NICE accepts oral B12 as an alternative to injections for suitable people at a dose the GP sets. There is no reason to take more than 2000 micrograms a day.
Safety profile
How much is too much: the NHS says 2 mg (2000 micrograms) or less a day from supplements is unlikely to cause harm, and there is no upper limit because the excess is passed in urine. There is no toxic dose in the literature and no UK upper limit. Very high oral doses occasionally cause acne like spots that settle when the dose drops. The thing to get right is not the amount but the cause: a low B12 with a normal diet needs a GP to check for pernicious anaemia or absorption problems before any supplement is chosen.
Guideline positions
NHS vitamins and minerals guidance for vitamin B12. NIH Office of Dietary Supplements fact sheet for vitamin B12 where one exists. The trial doses quoted above are from the sources listed on this page.
Practical framework
Capsules to reach the dose, from the Nutri Tailor range, all made in the UK: [methylcobalamin capsules](/products/vitamin-b12-methylcobalamin-capsules), 1000 micrograms per capsule, one a day for repletion, or twice a week for maintenance; [cyanocobalamin drops](/products/vitamin-b12-cyanocobalamin), 98 micrograms per drop, one drop a day covers a plant based diet with room to spare; [TRI-B12 liquid](/products/tri-b12-vitamin-liquid), 300 micrograms per ten drop serving, three forms in one bottle. To read your own result against the UK ranges, use the free blood test result interpreter. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.
Common misconceptions
That more vitamin B12 works faster: above the doses the trials used there is no extra effect, only more side effects. That the front of the bottle states the dose: read the per capsule figure and the serving size on the back. That the NHS figure is a toxic threshold: it is the level below which harm is unlikely, which is a different thing.
Sources
- 2024. B vitamins and folic acid. NHS.
- NIH Office of Dietary Supplements 2025. Vitamin B12: Fact Sheet for Health Professionals. National Institutes of Health, Office of Dietary Supplements.
- UK NICE 2024. Vitamin B12 deficiency in over 16s: diagnosis and management. National Institute for Health and Care Excellence (NICE).