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Pernicious Anaemia Society
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B12 injections

Hello, I wonder if someone can advise - I have been having Vit B12 injections for the past two weeks - 5 out of 6 injections so far but I'm still suffering from all the symptoms. How long does it take for the B12 to 'kick in'? If the injections don't have any effect, what would that indicate? I'm getting very concerned as I expected the injections to fix my problem.

17 Replies

Hi. Give it some time. You should feel a bit better but it took me 6 months to get back to feeling normal. I think it depends how bad your symptoms have got. I was really suffering, so took a long time to build my strength back up. Takes a while for your body to rebuild. 😊


Thanks for your advice everybody - very reassuring.


Hi :-)

Unfortunately that is one of these how long is a piece of string kind of questions. :-( Everyone takes different lengths of time to improve. For some their symptoms can feel a bit worse as the body begins to heal and "wakes up" a bit more.

If you were anaemic when you were diagnosed it can take a while (~120days) for your red blood cells to be fully replaced so improvement may well not be instantaneous unfortunately.


Thanks for your advice everybody - very reassuring


It took me 8/9 injections to see any improvement, and they were very minor. After that some improved slowly. A year later everything has improved but some only a little. Give it time.


Thanks for your advice everybody - very reassuring


As the others say, it will take a while. I started to feel better within a few weeks of the loading doses but it took several months and an adjustment to my injection timing to get back to approaching normal. It's something you just need to be both patient and persistent with.


Thanks for your advice everybody - very reassuring



I've assumed you're in UK.

"5 out of 6 injections so far "

Are your GPs proposing to give you an injection every 3 months after loading injections have finished?

This pattern of treatment reads like the standard UK treatment for those with B12 deficiency without neuro symptoms.

Patients with B12 deficiency and neurological symptoms are supposed to get more intensive pattern of treatment eg a loading injection every other day for as long as symptoms continue to get better (this could in effect mean loading injections for a period of several weeks even months as long as symptoms continue to get better) then once symptoms are stable it's an injection every 2 months.

Untreated or inadequate treatment of B12 deficiency can lead to permanent neurological damage. Some people develop SACDSC (sub acute combined degeneration of the spinal cord). If you are a PAS member , there is an article you can access on SACDSC in PAS library section. I believe some people on forum have showed this article to their doctors as an example of what can happen if the correct level of treatment is not given.


I believe Martyn Hooper, the chair of PAS, has SACDSC. Link to his story underneath.


B12 deficiency with neuro symptoms

Do you have neuro symptoms (eg tingling, pins and needles, balance issues, memory problems, tinnitus plus others)? See lists of b12 deficiency symptoms below.


pernicious-anaemia-society.... See Symptoms Checklist. I gave my Gps a copy of this with all my symptoms ticked.


See links below for more details on UK B12 treatment for those with neuro symptoms.

1) BNF (British National Formulary) Chapter 9 Section 1.2


2) BSH Cobalamin and Folate Guidelines

Info on UK B12 treatment is about a quarter through document.


Have you had an IFA (intrinsic Factor Antibody) test? This can help to diagnose PA (Pernicious Anaemia). The IFA test is not always reliable and it is possible to have PA even with a negative result in IFA test (Antibody Negative PA).

BSH flowchart

Flowchart below makes it clear that in UK patients who are symptomatic for B12 deficiency should have an IFA test and start initial B12 treatment. Flowchart also mentions when Antibody Negative PA can be diagnosed.


Other B12 info

1) Pinned posts on this forum

2) BMJ B12 article


3) PAS (Pernicious Anaemia Society) website


PAS tel no +44 (0)1656 769 717

Martyn Hooper's blog (chair of PAS)


4) B12 Deficiency Info website

Lots of b12 info and an interesting blog too.


5) b12d.org website


6) book "What You Need to Know About Pernicious Anaemia and Vitamin B12 Deficiency" by Martyn Hooper

7) book "Could it Be b12" by Sally Pacholok and JJ. Stuart

I am not a medic just a person who has struggled to get a diagnosis.


Wow, what a comprehensive and helpful reply - thank you! I'll print this off and take it with me to my GP (yes, in the UK) as I have almost all the neurological symptoms. Armed with your information, I shall be able to insist on further injections. Thanks again, Sleepy Bunny.


Hi again glaconmare

If you haven't looked at it yet, I would recommend reading fbirder 's summary of B12 documents before next appt. Link to his summary in third pinned post on this forum.

His summary is full of useful quotes from mainly UK B12 documents that have helped me to argue (politely) against some common misconceptions about B12 deficiency amongst GPs , nurses etc.

Unhappy with treatment?

Link about writing to Gps about b12



HDA patient care trust

UK charity that offers free second opinions about diagnoses and treatment



Great - thanks. Will do.


I am (was) a very active 68yrs old male, cycling an average of 600+ miles a month and walking some 40-60 miles a week, then about 6 months ago I noticed my endurance and strength were falling. After months of telling myself it was just a hangover from a long running head and chesty cold, I was diagnosed last Nov with PA and B12D, and was started on the every other day loading phase of 6 B12 injections and folate, I started to "feel" a lot better quite rapidly. Then despite still having most of the standard neurological symptoms, numbness in feet and severe in left calf, pins and needles in toes and constant tingling sensation in fingers and hands, memory recall issues and tinnitus I was put on the 12 week cycle "for the rest of my life". 5 weeks later I collapsed while out and after consulting with the doctor and hematologist, and thanks to the reference material from this site, I demanded and was put on weekly B12 injections and daily folate "until all the symptoms have gone". For the first 5 weeks there was a distinct fall off from the recovery after 4/5 days. I am 7 weeks in on the weekly B12 now and the fall off has stretched to 5/6 days. Some of the neuro symptoms appear to be receding too which is great, but still a long way to go. It does take time and everyone is different. Read the links above, get the right treatment regime for you in place and it should slowly start to come round. Good luck in the future.


Thanks for your help and advice - I'm afraid I don't quite understand what you mean by 'a fall off from the recovery' though. Could you clarify, please?


My apologies if it wasn't clear. 24hrs after having my injection, the improvement for me (recovery) is very noticeable and many of the symptoms start to reduce, then initially after 4-5 days I am falling back to where I was, numbness and pins and needles symptoms coming back, increased tiredness and any physical exertion or exercise resulting in breathlessness and tiredness and falling asleep. Currently, after 7 weeks on this weekly regime, I am now lasting 5-6 days before going backwards as regards symptoms.


No, you were very clear - it was me! I now understand what you were saying and it made sense the first time - the brain, of course, isn't working! Thanks for your information - thanks to the kind replies on this site, I realise now that I'm probably not getting enough B12 and need to speak to my GP.

I really appreciate everyone's help and feel in a much stronger position now to demand the proper treatment for my problem!

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