When can I expect to feel the effect from B12 injections?


I 'm very new in here - and from Denmark so please overbear with my English;-). I was diagnosed with B12 defiency just 4 days ago shown in a bloodtest. There doesn't seem to be anaemia.

I'm feeling very, very tired and fatigue among other typical symptoms due to b12 defiency.

I'v received two injections so far. The plan is to have 5 injections 2-3 days apart. Then, probaly 1 injection every 3 months.

Can anybody tell me when I can expect to feel the effect from the injections? Especially when it comes to feeling tired and fatigue.

Any comment will be gladly received:-)) as I can't find any Info on this. My doctor says within a week, but he doesn't seem to know a lot about this desease.


34 Replies

  • I'm still feeling tired after 18 months, everyone is different, one nurse told me it all depends on how long you were undiagnosed for as the body needs to make new supplies of blood in the bone marrow? At present I find I have a window of 3 weeks when I feel back to my normal self just after my injection. Also I'm constantly fighting for insight into this illness from my doctor, which I'm finding very stressful.

  • Hi Nettie,

    Ideally try to get your next B12 jab before you sink to rock bottom again...I know its terribly hard to get more frequent B12 treatment..but try..

    Kind regards,


  • Dear Nettie.

    Thank you so much for your reply.

    I´m sorry to hear that you have been feeling tired for so long.

    I can´t help but asking that even though you are still feeling tired after 18 months, have you felt any improvement at all (just a little less tired at all) during this time after you started getting the injections?

    Kind regards,


  • HI I'M also new to this and after the B12 injection feel dreadfully sick and depressed, after about 3 weeks i'm fine but 2 months in I get the shakes and tingles in my hand and itchy feet and start to go down hill my nurse tells me its normal think i would rather fore go the injections and just feel tired the shakes are some thing i can do with out … pugsly

  • Have u tried B12 vitamins? Multivitamins are ok, but the deficiency may exist. Try boosting your b12 levels that way. I find Over The Counter vitamins a great way to boost my levels.

  • Hi Anja,

    I am sorry you have to join this PA boat, and it may take a bit of time to feel the benefit of the B12 jabs. It depends on the person as nettie says, we all are di8fferent. Some people feel the benifity within a week others weeks others more months. I went back to Gp initially saying "these B12 jabs are doing nothing, are you sure you've got this right?". But after some 3-4 months I did feel a lot better (stronger and awake etc) , and started to rely on the B12 jabs to keep me well.

    So we all are different, it helps if you eat well, give your body a chance to get better, give it time, rest if you can and possibly take a multy vitamin, to avoid any temporarily shortages of other vitamins/ mins that are needed in the renewed blood production process with the added B12.

    But you should eventually feel a lot better, I hope its sooner than later for you!

    Kind regards,


  • Hi Marre.

    Thank you so much for your reply.

    I must say I hope that it won´t take 3-4 months to feel better. I´m afraid that my doctor will stop the injections if there´s no signs of improvement very fast. The doctors think I should feel better within a week, but I´m afraid it will take longer since my B12 level is very, very low. It´s also like they don´t take this illness serious enough. At the Clinic where I go there´s 3 doctors and when I came in for the second injection he asked if I drink enough water during the day. What´s frustrates me is, that I´m doing a great deal and always have to live healthy in any way - and taking vitamins and mineral supplements with extra B-vitamins.

    So it worries me that my body of some reason don´t absorb b-12. Have you felt worried as well?

    Kind regards,


  • I have had my very first injection today so I am interested to find out how long it takes p

  • Sorry pressed wrong thing lol -for people to feel less fatigued I have been feeling unwell for years and only just found out I have vit B12 deficiency I also have thyroid problem so hopefully I will soon feel better, but it not nice getting all these problems I don't know anyone with these problems so all the best let me know how you get on please

  • Hello I just started B12 injections and have taken 2. Dr has given me 1 per day for 7 days then one a week for a month then one a month for ??? I hated giving myself the shot but after only one shot I feel better. I take metformin and it had depleted my own b12. levels should be within 211-946 range and mine are 135. so my muscles were so weak just getting out of a chair is a chore. I was so tired all the time. I do feel much better and I hope you have the same experience. Good Luck

  • Hi Anja,

    Yes I was worried and upset that my body was not perfect anymore is what I remember, but pleased that I did not have "Mad Cow's decease", which is what I thought I had (jelly legs, confused brain). Its also not nice to know this is for life, somehow you now depend on a jab to stay alive is a strange concept I found initially. And then comes the why, why it has gone wrong, it took me years to find out that it runs in my family, and the reason is not known. I've seen a haematologist, neurologist and gastro over a period of more than 10 years after diagnosis in 2001. I still have no real answer as to why, but all say so much is still unknown about PA/ B12 def, and for what ever reason I must stay on the B12. Not that I'd ever try without now, its given me my life back.

    What is important is that you get the right treatment that suits you, and have some monitoring of bloods as over time other deficiencies and or issues can crop up. Ideally your treatment is individual to your needs, this is unfortunately hard to get, the current guidelines in most countries seems the same treatment for all, no matter what the reason was, or how you feel, although a difference exists if you are diagnosed with neurological problems caused by a prolonged B12 def. If you are lucky you get (or find) a supportive Dr, one that will recognise that one size does not fit all. If you are lucky the standard treatment will be fine and you will feel fine in time!

    I hope you will, but be patient, it can take time. It takes 3-4 months for new blood cells to replace all the faulty ones produced by the lack of B12 .

    Both my daughters are on B12 treatment, for their sake I would like a reason, but no there is not one common one for us at this time. My daughters are fine on standard B12 treatment, their serum levels were low (def) but not as low as mine (I was diagnosed late), so perhaps it is a matter of how long you have been deficient to how long it may take to feel well again, and how much B12 you need to achieve that.

    Eitherway It will be worth the wait though! You will feel a lot better in time!


  • Hello Mare,

    Thank you for telling us about your experience and history. When my B12 level was tested my doc also checked my Thyroid. My B12 was very low and she started me on weekly B12 shots for eight weeks, then the regimen extended out to monthly while taking oral B12 as well. (I'm 72, live in U.S.) I've checked the British guidelines but don't remember seeing anything about receiving oral along with injections. Any feedback is appreciated.

    Also, my thyroid function was low, with elevated TSH of 5.95 (previous tests were always normal range, 0.35--4.0) and T4 of 0.8 (normal 0.8--1.5). My doctor deferred action on this issue.

    I'm wondering if those of us who have both low thyroid function and B12 deficiency take longer to respond to what is considered adequate treatment by British guidelines? Again, I'd like to hear opinions and/or receive sources for follow up.

    Thank you all,


  • Hi Linda,

    I know little about thyroid conditions, but do know about some guidelines and treatments for B12 def/PA in other EU Countries, and hum some other countries have a far more generous approach to regularly topping up the B12 (jabs) than UK, in UK one has to survive on once every 3 months hydroxocobalamin injections, whilst in some other EU Countries the same hydroxocobalamin is recommended every 2or even monthly. In UK oral B12 is only recommended as treatment for diet related B12 def. These guidelines are in the BNF see this link:

    Official UK BNF (British National Formulary) guidelines


    (One will have to register to access it PA is chapter 9 section 1.2 ).

    I believe in US the B12 used is mainly cyanocobalamin, which is "shorter lasting" than hydroxocobalamin. Maintenance treatment with cyanocobalamin is once ever month as standard.

    I hope answers some of your questions, I believe that out of UK residents can not register for the BNF and as it is copy righted no one can paste or copy from it.


  • Hi Marre,

    Thanks for your response and omformation. Yes, cyanocobalamin is the injection I receive in US, not hydroxo-

    I obtained access to the Guidelines (pdf) at this URL:


    Appreciate your help and experience,


  • Marre, If you have read, or do read, the CDC source I noted in my reply to Gambit I'd be interested in your thoughts about it.

    Thanks, Linda

  • Hi Leilanilea,

    I have read some of the link (CDC source) and yes it seems to be good advise and up to date.

    A bit pasted for others to see below, Marre.


    "Initial Assessment

    The CBC, smear, and the serum cobalamin (B12) test should be included in the initial laboratory assessment of vitamin B12 deficiency.

    After conducting a thorough history and physical examination, if you suspect vitamin B12 deficiency, you should include a complete blood count (CBC), peripheral blood smear, and serum cobalamin (B12) as part of the initial laboratory assessment.58 The serum cobalamin test is readily available and generally affordable, and can detect low serum vitamin B12 levels even among patients who are not anemic.59,60 However, not all patients with a vitamin B12 deficiency will have hematologic manifestations. As Carmel succinctly noted, “the proscription that cobalamin deficiency should not be diagnosed unless megaloblastic changes are found is akin to requiring jaundice to diagnose liver disease.”11

    While serum vitamin B12 concentrations are generally accurate,61 many conditions can complicate the interpretation of vitamin B12 laboratory values. Falsely low values have been associated with multiple myeloma, oral contraceptives,62-64 folate deficiency,58-59 and pregnancy.10 Additionally, a low serum B12 level does not automatically mean a deficiency. From 20% - 40% of elderly people with low serum B12 levels have normal metabolite (homocysteine [Hcy] and methylmalonic acid [MMA]) levels and should not be considered deficient. 11

    “Accepted lower limits of serum B12 levels in adults range between 170 and 250 pg/ml; however, higher levels (but less than 350 pg/ml) have been recorded in 15% of ostensibly healthy elderly patients with other findings suggestive of a deficiency state, most notably increased levels of serum methylmalonic acid. The true lower limits of normal serum B12 would therefore appear to be somewhat poorly defined.”

    Ward, 2002

    Sometimes, a true cobalamin deficiency will not be detected by the serum vitamin B12 test. Some examples of falsely normal serum cobalamin results might be seen with (but not limited to) liver disease,58 myeloproliferative disorders,58 and renal insufficiency.4,65 If a patient has clinical evidence of vitamin B12 deficiency and a normal serum B12 level, it is important to evaluate further.


  • Hi Linda,

    Having read some more:

    I think the diagnostic section is good.

    But the treatment section is very rigid, does not seem to allow for the individual's needs. There can be so many other factors that can influence how a person actually deals with the injected B12 I think. This also applies to tablet forms of B12 as addition to injections, some people will be OK with that, others not, depending on how much is absorbed passively, and how much recycling of B12 takes place (bile), which again can be very different per person with the same PA diagnosis.

    I hope you appreciate my comments,

    Kind regards,


  • Hi Marre,

    Thanks, I definitely appreciate your comments about CDC article. Re: Treatment recommendations, did you look at Table 6, "Examples of Treatment Regimens for Clinical Vitamin B12 Deficiency?"

    I'm not questioning your concerns that the CDC article is too rigid about treatment recommendations, but the information in the Table seems to suggest allowance for adjustment of routines and is taken from approaches suggested by Stabler, Allen and Carmel. In general are you questioning the dose or the frequency, or both? I'm not being argumentative, I'd really like to know your thoughts on this. Although my physician realized the need for treatment, I had done research by then and seen examples of loading doses, and did suggest to her that at least weekly would be best initially, and she complied.

    As this article is part of a physician education course, I was so glad to see the following: "While the route, dosage, treatment timing, and follow-up might vary somewhat, there is no question about the decision to treat patients with pernicious anemia or with a low serum B12 level and hematologic or neurologic signs or symptoms without pernicious anemia (clinical vitamin B12 deficiency). Once treated for a vitamin B12 deficiency due to pernicious anemia or other irreversible severe problems with absorption, patients need to continue some form of cobalamin therapy for life."

    Any resources you recommend are appreciated.



  • Hi Linda,

    There are those that do not cope on the maintenance treatment recommended in the CDC article, once every month IM or subcutain cyano jab, and there are those for which oral does nothing at all. There seems to be no mention for treating the individual according to their individual needs. For me oral B12 did nothing, proven by a lack of any increase in serum B12 levels (and symptoms). One of my daughters initially went on high doses of perscribed B12 vitamins for 3 months to see if this would address her deficiency, it did nothing to raise her serum B12 she stayed deficient. If I inject every 2 weeks cyano, my serum B12 levels drops to low, for me to feel well. On standard NHS maintenance B12 (hydroxocobalamin) treatment my serum B12 levels dropped to B12 230 ng/L = 170 pmol/L. Others may have triple that level but still feel unwell. We all are terribly different. People can have more than one problem with taking up , storing and metabolising B12, and recycling of B12. Normally a body is very careful with B12 and will recycle it, this process can also be broken by completely other issues on top of say genetic PA. One size treatment does not fit all.

    Perhaps read this : WHO on B12 ,

    WHO on B12:

    whqlibdoc.who.int/publicati... ... chap14.pdf

    Kind regards,


  • The link is out of date for the WHO document I think, anyway this topic on the old PAS forum has more upto date links and is perhaps more relevant, see:


  • Thank you so much, Marre. More later, Linda

  • Sorry to hear you are struggling - and dealing with doctors can be really frightening. My experience was of really getting absolutely no information from anyone and even being told - that symptoms I was describing were not symptoms of B12D and it couldn't be B12D anyway because I was receiving shots, though on reflection I don't think the loading shots were done correctly. My diagnosis was done as result of a blood-test in hospital after a fall that broke my ankle ... and nobody bothered to ask me if I had had neurological symptoms (eg problems with balance ... and the tiredness as well) so I had just the 6 loading and then 2x3 months. The recommendation in the UK if neurological symptoms are showing is once every other day until symptoms improve and then once every 2 months.

    People do react very differently - and even then it can be different for the same person. Last October (having talked to a locum who seemed to know something about B12 - and being told I needed injections at least every 3 months and most of his patients ran out of juice after 2 so don't necessarily hold out for the 3 months) I noticed the improvement within a couple of hours ... and it lasted for about 6 weeks. The last injection I had - during a period when I kept having colds which really seemed to wipe out any benefit - the effects lasted only a couple of days ... hence the rather disappointing trip to the GP

    I was so upset after the last encounter with my GP that I decided that as far as possible I was going to self-medicate and started using high dosages of a nasal spray of hydroxocobalamin. Within a week I was feeling much better - the energy seems to go start dropping after about 12 hours so when I feel tired I take another squirt. Last year I couldn't climb a ladder. This March I could scarcely walk and getting into and up from a chair was a real struggle - sometimes requiring several attempts. Within a week of using the spray my balance was much better and within a couple I had enough energy to play a full game of bowls without having to sit down each end ... or taking 1/2 hour to change my shoes.

    The PAS has published a couple of books - Pernicious Anaemia: the forgotten disease - is aimed partly at trying to get doctors to realise that PA isn't a one-size-fits all condition. A lot of people also recommend 'Could it be B12'. It might be worth purchasing one of these and giving it to your doctor. The PAS book is quite an easy read. I haven't read the other one (yet) Suspect neither is available in translation unfortunately - but may be there is an equivalent of PAS or a B12Deficiency group in Denmark that has produced something similar.

    Please feel free to post here because a lot of us do have problems with finding a solution that works for us ... getting information from our doctors ... and even being able to communicate with our doctors.

  • Hello Gambit,

    Although Britain seems to be ahead of most countries in their knowledge and guidelines for B12 deficiency, I'd like to recommend a source of info online that is a start in educating US providers about diagnosis and treatment: "Why Vitamin B12 Deficiency Should be on Your Radar Screen." You will reach it by searching that title on internet. It is from the Centers for Disease Control (CDC) and is aimed at healthcare providers, but is lay-reader-friendly. Ignore the top part and scroll down a bit.

    Thanks, Linda

  • Thanks - looks really interesting. For others in UK, and for Anja link came up as

    cdc.gov/ncbddd/b12/index.html, and then delve into the details below.

    Useful to see 1 in 31 as a figure for prevalance as the impression I get is that it is considered to be rare in the UK and I certainly wouldn't regard that as rare :)

  • Hi Anja

    I was diagnosed with very low b12 a year ago. Like you I had no anaemia and also like you I felt worse before I felt better. Although some of my symptoms improved significantly within 2 weeks such as the headaches and tingling sensations, the fatigue and muscle weakness became so bad I asked my GP to give me a break from the loading doses in order to let my body recover! I also had some side effects from b12 such as extreme thirst and spots all over my chin. Once the loading doses were finished I did start to feel better. My mood improved and gradually my energy returned. I now have an injection every 8 weeks but, like many people, some symptoms return after about 3 weeks so I supplement with patches and sublingual tablets.

    Stay positive Anja. I do hope you feel better soon.


  • Hi Megan.

    Thank you so much for your reply. Sorry not to get back to you sooner. I´m a mother of four, my youngest, a babygirl is only 5½ months old so it´s so hard to get to the computer. How many loading doses did you get? My doctor says the standard treatment is 5 injections 2 days apart. Then a 6th injection 3 months later. It´s in such contrast to what I can read from many in here that need injections a lot more often. Like you, I´m also experiencing spots on my face. I´v had 4 injections so far. What I´m really looking forward to is for the fatigue to lift of...Glad to hear that I´m not the only one with b12-deficiency, but with no anemia. Do you know what causes your low B12 level?

    Kind regards,


  • Hi Anja

    It must be hard for you at the moment with such a young family but hopefully you will feel the benefits of the injections very soon.

    I had 9 loading doses in total: 3 a week over a month (I had 1 week off!) In England the guidance for GPs is to give alternate day injections until there is no further improvement for patients with neurological symptoms. In my case this was in the form of tingling and weird sensations on my limbs and face. Now my injections are 8 weeks apart. (If there is no neurological involvement the guidance is to give loading doses alternate days for 2 weeks then injections every 12 weeks)

    I believe the spots on your face show that your B12 injections are working so hopefully that's a good sign!

    A recent blood test showed I have antibodies to parietal cells in my stomach. If these are destroyed they cannot produce a substance called intrinsic factor which is necessary for the absorption of B12. My doctor has told me I have pernicious anaemia even though I have no anaemia; confusing isn't it!!

    Hopefully your GP will be monitoring you to see how you are responding to the injections and investigating you to find the cause of your low B12. Keep talking to him or her and let them know if you are still struggling; you may need to be referred to a specialist. I hope this makes sense to you. Your English is very good!

    With very best wishes


  • Hi,

    I have high need for B12. I have many symptoms of low B12. But, I do not have Pernicious Anaemia. I do have a methylation defect called (MTRR) where my body can't regenerate or make Methylcobalamin which is the active form used by the body.

    I can get a B12 blood test done and it will show that I have high levels of B12, like 1700. High normal levels are around 800 I believe? From what I understand is that my body can't convert standard B12 to its active form so I have all this other B12 floating around in my blood not being utilitized. Probably didn't help getting B12 injections that contained the standard form Cyanocobalamin.

    I had two tests that showed I had a need for B12 even though my blood had high levels. One was NutEval from Genova Labs. And the other was SpectraCell (spectracell.com). I like SprectraCell as it looks to see what nutrients are actually getting into the cells not just what's floating around in your blood. I believe that it how that test works.

    I started taking 1500mcg of Methylcobalamin in dry capsules form, which kinda helped. But it wasn't until I started taking a 5000mcg Active B12 sublingual that I really noticed a difference. This particular sublingual contains 4000mcg of methylcobalamin and 1000mcg of Adenosylcobalamin.

    I've taken 2000mcg Hydroxocobalamin sublingual before but not sure I noticed that big of a difference. It's possible my body can't convert it to Methylcobalamin. I'm not sure.

    I have had some blood work that showed that I had a bunch of small red blood cells I think, but doctors couldn't tell me why. Low B12 might be why?

    Anyway, does anyone know what symptoms might occur when starting higher doses of active B12? I definately feel better, but....I imagine as your body repleats B12, a lot of changes could occur, especially if you've been low for many years. Also, I've read that your liver stores 2-3 years worth of B12, anyone read this? I would assume it stores methylcobalamin? How long does it take to restore your B12 levels?

    I'v read at the following site that you need to keep you eyes on potassium and ferritin levels as you start taking higher doses of B12. Not sure about the potassium, but I guess when you start making more red blood cells, more iron is needed??? I'm going to have my ferritin levels tested hopefully this week. b12deficiency.info/home. This is a good site (I think from the UK) about B12 deficiency. But doesn't have much info on methylation issues like (MTRR) as being a reason for having low B12.

    Anyway, there is quite a bit of info on the web about MTRR. You can have methylation tests done to see if you have any defects that might be causing your low B12 symptoms.

    Anyway, love to discuss more about B12 stuff. Thank you.

  • Hej Anja. Jeg faldt over denne post da jeg søgte svar om B12 på nettet. Jeg er lidt nysgerrig efter at høre, om B12 behandlingerne nogensinde kom til at virke for dig?

  • Hej Maiken.

    Behandlingerne kom heldigvis til at virke for mig, men der gik ca. 2 måneder. Det kan vist variere meget mht., hvornår man mærker en effekt.

    Mange hilsner,


  • Dejligt at høre - har det nemlig som du havde - så rart at høre, at der kan være lys forude :-)

  • Der er helt bestemt lys forude. Men man kan godt miste modet, når det tager så lang tid at mærke en ændring. Min læge sagde, at jeg ville kunne mærke, at jeg fik mere energi efter en uge. Det havde han så ikke helt ret i...Det hjalp også for mig at læse, at andre også havde været lang tid om at mærke en ændring.

  • I have the same sytoms I have to take the shots 7 days then 1 a week for four weeks then once a month, I have had three yet I still feel so wiped out tried, its like I have to make myself just do the basic things, I hope u feel better soon

  • Anja and all, I have been on injections for years. I self inject once monthly. If I am under lots is stress or have been ill, I feel the affects of the meds wear off sooner..but, if I am healthy, take care of myself, I do fine. Oral or sprays do not work for me. I rather take the injections than feel tired, achey and foggy brained. I keep in mind, it is a life time, but...the prognosis is good and not terminal like many of my friends experience with other ailments. All will be good. Feel well..😊 ty and kindly for allowing me to share. Penny

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