How long before B12 injections start to work?


I'm new to all this and basically just got diagnosed a couple of weeks ago with PA and I've also had iron deficiency anaemia for a good few year too. I'm generally feeling rubbish, have absolutely no energy, no patience and snappy plus only getting a few hours sleep a night. I have also become a bit low in mood..I thought this was all down to not sleeping. Doctor is convinced I have depression and has given me anti depressants even though I've never had it before and I really think it's more to do with the B12. I've also just had my 4th loading dose injection this morning and then after the 6th I've to have 1 every 12 weeks depending on my levels when they get checked again. My question is how soon am I likely to see the effects? I don't feel any better yet and I'm currently on the sick from work while I'm not sleeping and feeling this way. I can't seem to concentrate on anything and have really loud tinnitus on a night time which doesn't help the sleeping. I just wanna be back to normal!

11 Replies

  • Hi,

    I've assumed you're in the UK.

    "Doctor is convinced I have depression and has given me anti depressants"

    I have read that depression can be a symptom of PA and B12 deficiency. Some drugs can affect the uptake of B12 in the body.

    "then after the 6th I've to have 1 every 12 weeks depending on my levels "

    Do you have any neurological symptoms?


    Symptoms list in library section

    The reason I'm asking is that the NHS treatment for B12 deficiency with neurological symptoms is more intensive than the treatment you mention.

    The info on treatment can be found in the BNF (British National Formulary) Chapter 9 Section 1.2 The BNF is copyrighted so can't reproduce info here but this link contains similar info.

    Info on recommended treatment is also in the "BCSH Cobalamin and Folate Guidelines". The BCSH Cobalamin Guidelines were updated in 2014 so are recent. I found them useful to read and I gave my GP a copy. The PAS have a summary of the BCSH Guidelines in library section on website. Sadly some GPS are not aware of these guidelines.

    If a patient is diagnosed with PA, treatment is for life. Some patients with PA have had their injections stopped because of high levels of B12 in their blood.

    Has your GP checked your ferritin , folate and full blood count?

    Other useful links


    Could it Be B12 by Sally Pacholok

    "What You Should Know About Pernicious Anaemia and Vitamin B12 Deficiency" by Martyn Hooper

    Some people find they need B12 more often than the standard level of treatment. The NHS injections are usually hydroxycobalamin but some people on this forum have said they respond better to other forms of B12 eg methylcobalamin, cyanocobalamin and adenosylcobalamin.

    I am not a medic, just a person who has struggled to get a diagnosis and wants people to have the info to make their own decisions.

  • Thanks for the info, will have a good look through. It will be good to know a bit more about it. Doc didn't say wether they'd checked for anything else just iron, B12 and thyroid, Iron level was at 8 and B12 was at 60 apparently..but I do have to go back for more tests to check why I don't absorb the B12. I did have tinnitus really badly but that is one thing that's started to ease, and I also get dizzy spells and feel faint every now and again and have for ages now..haven't seen the Doctor about that before because I'm deaf in one ear so just put it down to an imbalance because of that. Maybe I should mention it next time I'm there. Looking at that sympton list theres quite a few things I have that I never even thought could be down to B12. I spoke to the nurse when I got my jab today and she said it could take a few weeks after the loading dose to start feeling the benefit, but that seems like a long time to still be feeling rubbish.

  • Took a couple of weeks for me to feel better after loading doses and now on holiday feeling so much better and near normal. It's such a relief. Hope you feel better very soon

  • I also wondered if you had ever been tested for coeliac disease.

    "had iron deficiency anaemia for a good few year too"

    Iron deficiency is common in people with coeliac disease.

    The Coeliac UK website also mentions that it is possible to have coeliac disease with negative test results.

    PA is an auto-immune condition and they sometimes come in clusters.

    You mentioned you had had thyroid tests. The thyroid forum on HU is very active.

    The reason I mentioned the FBC (Full Blood Count) test in my previous post is there can be useful clues on that. Low iron makes red blood cells smaller, low B12 and/or low folate makes red blood cells bigger. If a patient has both conditions then red blood cells can appear "normal" .

  • You are not alone in this I have diagnosed with PA have got seven shot already and I'm not feeling any better I have the same symptoms like you skeepless night ,low energy lf I dont take a sleeping tablet I dont sleep most of the time my GP told me that it would make me sleep I feel frustrated most time I need to feel well again

  • You could be me! Exactly the same symptoms I was offered antidepressants a few years ago which I refused then HRT which I accepted as I assumed it was menopause but when I started forgetting common things and experiencing pain and pins and needles in my feet and extreme fatigue I had the PA diagnostic tests. Now although my GP is knowledgable and supportive & I've had loading doses I may consider self injecting daily to prevent further neurological damage as I feel good for a couple of days then drop back. My serum blood level is over 1000 but the active level is only 148 so it doesn't look like I'm absorbing it properly. I'm booked to see a hematologist but not hearing much joy from others who have seen hematologists & most seem to be self managing. This is not ideal but with our Govt trying to save money by reducing acceptable B12 levels and a lack generally of knowledge and interest of PA from the medical profession I can understand why people want to take it into their own hands. Maybe have B12 injections more often as in my case after a couple of months of twice weekly injections it has helped stomach issues, sleeping, memory,energy and mood.

  • If your GP is knowledgeable and supportive, as is mine, I suggest you try various intervals between injections and keeping a symptom diary.

    Originally my GP and I agreed on weekly jabs, which he unilaterally changed to monthly. So I phoned him and we agreed a compromise of fortnightly jabs.

    I managed to last two weeks, and felt crap. The next time I only managed 10 days (today) before I needed another fix. When I see him again ,in four weeks time, I'm sure my diary, plus my worsening neurological symptoms, will persuade him that weekly jabs are required.

    It may be highly unpleasant to go without an injection for a week, but if you can last that long, and present your doctor with a daily record of how awful it made you feel, then he should realise that you know the frequency of jabs that you, personally, require.

  • Thank you fbirder! I will do that, it's very up and down. Weirdly I just realised I received exactly the same results for B12, active B12 & folate two months apart which doesn't seem to make sense? Early September test results showed B12 >1476 Active B 12 >128 Folate >54.5 then after twice weekly B12 injections I tested again and received exactly the same results early November. GP wants to go to monthly injections based on this, I didn't realise the results were the same while I was with her i just noticed it on the tests she emailed me. Not due to see her for a while. Does this make sense?

  • Fbirder ignore my last comment.. I just realised the results are > greater than and not exact levels. Labs here don't provide exact levels if you're greater than the normal range cut off point....

  • Yes your right

  • You do not give any details about your diagnosis of PA. However, it may be that your symptoms are not related to this diagnosis. That would be one reason why you are not improving on the injections. That does not mean that I am saying that you do not have PA. Only that the symptoms may be caused by other problems.

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