Hematologist
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How long B12 treatment continues, and what decides it | CION Cancer Clinics
If your body cannot absorb B12, as in pernicious anaemia (a low haemoglobin caused by poor B12 absorption) or after stomach surgery, injections usually continue for life, with a top-up every few months after a starting course. If diet or a medicine caused the low level, treatment often lasts months and may move to tablets. This page walks through the usual course, what decides its length, and when not to wait. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- How long will you need B12 injections?
- What does a typical course of B12 injections look like?
- Why do some people need injections for life and others do not?
- How will you know the injections are working?
- What do families often get wrong about stopping B12?
- Is your treatment likely to be short or lifelong?
- Common questions about how long B12 treatment lasts
The short answer
How long will you need B12 injections?
It depends on why your B12 fell. If the cause is one your body cannot get past, injections usually continue for the rest of your life. If the cause can be put right, treatment often lasts for months and then stops or changes to tablets.
When the cause stays
Some people cannot take B12 in from food at all. The most common reason is pernicious anaemia, where the immune system stops the stomach making the helper that B12 needs to pass into the blood. Surgery that removed part of the stomach or the lower small bowel does the same. Here the gap never closes on its own, so the injections are a lifelong top-up, not a course you finish.
When the cause can be fixed
Other people absorb B12 perfectly well but were not getting enough, or a medicine was lowering it. A strict vegetarian diet with little milk or curd is a common example in Telangana and Andhra Pradesh homes. Once the diet or the medicine is sorted, many people move from injections to tablets, or to an occasional injection.
You often do not know the cause at the first injection. Treatment starts first, and the length of it is decided once the tests come back.Week by week
What does a typical course of B12 injections look like?
This is the usual shape. Your own doctor may space the injections differently, and that is not a sign anything is wrong.
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The starting course
Treatment begins with several injections close together, usually over the first couple of weeks. The aim is to refill the body's stores quickly. Most people have them at a clinic or from a nurse, into a muscle in the arm or thigh.
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A longer start if your nerves are affected
If you already have tingling, numbness, unsteady walking or memory changes, the frequent injections usually carry on for longer. They continue until your doctor sees no further improvement, because nerves recover more slowly than blood.
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Tests to find the cause
While the starting course runs, you may have tests for pernicious anaemia, questions about diet and medicines, and sometimes a stomach check. The result decides which path you go down next.
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Top-up injections
If the cause stays, you move to a top-up injection every few months. People who had nerve symptoms are often kept on a shorter gap between injections. This continues for life.
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Review, and sometimes a switch
If the cause was diet or a medicine and it has been dealt with, your doctor reviews whether injections can stop or change to tablets. A repeat blood count shows whether the red cells have recovered.
Not sure whether this applies to you?
Ask an oncologistWhy it differs
Why do some people need injections for life and others do not?
The length of treatment follows the cause, not the number on your first report.
Pernicious anaemia
The immune system blocks B12 from being absorbed in the gut. This does not go away, so injections usually continue for life, even when you feel completely well.
Stomach or bowel surgery
Weight-loss surgery, or an operation that removed part of the stomach or the end of the small bowel, takes away the place where B12 is taken in. Top-ups are normally lifelong.
Also in this group
- Long-standing bowel inflammation
- Some ongoing gut conditions
Diet low in B12
B12 comes mainly from animal foods, including milk, curd and eggs. Once the diet changes, or tablets are added, injections can often stop. Some people keep an occasional injection instead.
A medicine lowering B12
Metformin for diabetes and long-term acid-reducing tablets can both lower B12 over years. Your doctor weighs whether you need ongoing tablets or injections while that medicine continues.
Never stop a diabetes or stomach medicine on your own because of a B12 result.Recovery
How will you know the injections are working?
Tiredness and low energy usually ease first, often within the first few weeks. The blood count takes longer to return to normal. Nerve symptoms are the slowest of all, and some may not recover fully if they had been there for a long time before treatment began.
Why a repeat B12 test may not help
Once injections start, the B12 level in your blood rises sharply and can look high for weeks. That number does not show whether your body is now absorbing B12 on its own. This is why doctors often do not repeat the B12 test to decide whether to carry on. They look at how you feel and at the blood count instead.
If symptoms come back before the next injection
Some people notice tiredness or tingling returning in the days before a top-up is due. Tell your doctor. The gap between injections can be changed, but that decision belongs to the treating team, not to a pharmacy or a relative.
What this page cannot tell you
It cannot tell you your own cause, your own schedule, or whether your tingling will fully settle. Reference ranges also differ between laboratories, so one result is always read alongside your symptoms and repeat tests.
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Commonly believed
What do families often get wrong about stopping B12?
"She feels fine now, so the injections can stop."
Feeling well is the injections doing their job. With pernicious anaemia or after gut surgery, the stores drain again once the top-ups stop. Symptoms can creep back slowly, and nerve damage that returns may not fully recover a second time.
"His B12 report is high, so he has too much."
A high reading after injections is expected. The body stores what it needs and passes out the rest in urine. It is not a reason to skip the next injection unless your doctor says so.
"More injections will make the tingling go faster."
Nerves heal at their own pace. Extra injections outside the plan do not speed that up. Your doctor already sets a closer schedule when nerves are affected.
"Once it is lifelong, nobody needs to review it."
Lifelong top-ups still need an occasional review. A blood count checks the red cells, and new symptoms such as tiredness or weight loss are looked at on their own merits, not blamed on B12.
Side by side
Is your treatment likely to be short or lifelong?
Usually a limited course
Usually lifelong
Low B12 from diet, with normal absorption
Pernicious anaemia confirmed by tests
A medicine that can be reviewed
Surgery that removed part of the stomach or small bowel
Often moves on to tablets once stores are full
Top-up injections continue at a steady gap
Reviewed with a repeat blood count
Reviewed now and then, even when you feel well
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Do not wait for the next injection if this happens
New or quickly worsening numbness, weakness in the legs, falls, trouble walking in the dark, confusion, or breathlessness with chest pain need a doctor the same day. Go to the nearest emergency department, or call 108 if the person cannot be moved safely. Take the injection record and the latest blood report with you.
Questions we are asked
Common questions about how long B12 treatment lasts
Will I need B12 injections for life?
Only if the cause cannot be put right. People with pernicious anaemia, or who have had parts of the stomach or small bowel removed, usually need top-ups for life. If your low B12 came from diet or a medicine, treatment is often shorter. Your doctor decides once the cause is known.
Can I switch from injections to tablets later?
Sometimes. If your gut absorbs B12 normally and the stores have been refilled, many doctors move people on to tablets. If absorption is the problem, tablets may not be enough. Ask your doctor whether a switch suits you, rather than changing on your own.
What happens if I miss a top-up injection?
Missing one by a few days rarely causes a problem, because the body holds some B12 in store. Book the next one as soon as you can and tell the nurse. Missing several in a row is different, as symptoms can slowly return. Do not double up without advice.
Does my B12 need to be checked after every injection?
Usually not. After injections the B12 level reads high and says little about how your body is coping. Doctors tend to rely on how you feel and on a blood count. If new symptoms appear, they may order other tests to look for a different cause.
Can a family member or local clinic give the injections?
Many people have top-ups at a nearby clinic or from a nurse, which saves travel from the districts. Some are taught to give them at home. Keep a written record of each date, and share it with your doctor at every review.
My mother is on metformin. Is her B12 treatment lifelong?
Not necessarily. Metformin can lower B12 slowly while she takes it, so her doctor may keep her on tablets or occasional injections for as long as the metformin continues. She should not stop her diabetes medicine because of this. The two are managed together.
Will the tingling in my feet fully go away?
It often improves, but nerves recover slowly and not always completely. Damage that had been present for a long time before treatment is less likely to settle fully. Tell your doctor if it gets worse on treatment, because that needs checking for other causes.
When should I see a haematologist?
If your blood count does not recover on treatment, if other counts such as platelets or white cells are also low, or if the cause stays unclear, ask for a haematologist's opinion. Large red cells that do not settle with B12 can point to a marrow problem that needs a closer look.
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Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Sources
- NHS — Vitamin B12 or folate deficiency: treatment
- NICE — Vitamin B12 deficiency in over 16s: diagnosis and management (NG239)
- NHLBI — Pernicious type of B12 deficiency
- American Society of Hematology — Low red blood cells: patient information
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
B12 injections vs tabletsHow the choice between the two is madePernicious anaemia explainedThe most common reason treatment is lifelongNerve symptoms from B12 deficiencyWhy tingling recovers slowlyMetformin and B12 deficiencyFor families managing diabetesB12 and folate hubEvery page on large red cells and low B12
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Not sure how long your B12 treatment should last?
Tell us what your blood report and injection record show so far. We will help you reach a haematologist who can look at the cause, not only the number.