How long before vitamin b12 tablets start to work?

Last week I was posting in the Thyroid section of this site – my GP reduced my thryroxine, I started to feel unwell, so I had a blood test. The test results came back showing my thyroid levels are fine. But apparently the B12 result arrived back at the surgery a few days after the other results (?) and it showed I’m low in Vitamin B12.

Doctor has prescribed B12 tablets, told me to see how I go, and if I don’t feel better by the end of Jan, to come back, have another blood test, and she may consider B12 injections. Fair enough – a problem has been identified and I’m being treated.

My symptoms are weird (although quite typical according to Google) fatigue, feeling faint and a bit dizzy. My ears are also ringing slightly. I was beginning to think I’d got flu.

I’ve only been taking supplments for 24 hours, so I’m not expecting to be doing cartwheels just yet, but can I expect to be feeling a bit better by Christmas? Feeling faint and dizzy is making it hard to go about my usual routine, although I’ve been prescribed Stemetil, and that’s helping a lot.

47 Replies

  • What are the tablets? Which type of B12 and what strength?

    Assuming you are in the UK, the only reason for a doctor ever to prescribe just oral tablets is when the B12 deficiency is known to have a dietary cause which is unlikely unless you are a strict vegan. B12 deficiency for any other reason should always be treated with hydroxocobalamin injections.

  • I will be collecting prescription shortly, and I will report back on what I've been given.

    I'm not vegetarian or vegan, and I eat a fairly regular diet. The doctor said she wanted to see if b12 tablets might help in the first instance, and went to say that if they don't, this then points to a condition that makes it harder for the body to absorb b12, and then injections would be the next step. And yes, I'm in the uk.

    But if my body struggles to absorb b12 from my normal diet, surely some supplements will help, even if I end up needing injections in the long run?

  • The most common cause of malabsorption is Pernicious Anaemia (PA). This is an autoimmune disease where your immune system attacks cells in the stomach so they don't produce something called Intrinsic Factor (IF). This is a protein that picks up B12 molecules and transports them out of the gut. Without IF this doesn't happen.

    Without IF some B12 will manage to make it out of the gut, but this is only about 1% - on average. Most people with PA find that oral supplements don't work.

    Waiting for a few weeks probably won't cause too much harm. But if your symptoms start getting worse - especially if you start getting pins and needles or numbness in your hand/feet - I'd go back to the doc and ask for injections.

    One of the jobs of B12 is to help produce the myelin sheaths around nerve fibres (a bit like the insulation on electric cables). Without these sheaths the nerves don't work properly. At its worst this can cause damage to the spinal cord, which isn't something you really want to happen.

  • I've begun research on cause and effect of Vitamin B 12 Deficiency as it may apply to me personally. My interest in the subject began when I dropped two brand named vitamin B 12 tablets in a glass of water, to learn how long it would take for the tablets to disolve. I was not surprised to see the tablets intact after four days. What I am learning about this vital subject, coupled with my personal interest in all aspects of vitamin deficiency, especially Vitamin B 12, will be submitted for review and subsequently published as part of a thesis.


  • The rate at which a B12 tablet dissolves in water will depend solely on two factors - the coating on the tablet and the bulk material. 99%, or more, of a B12 tablet isn't B12 (Solgar 1000 ug lozenge weighs 130,000 ug; Jarrows 5000 ug lozenge weighs 650,000 ug).

    What you've determined is that the particular tablets you looked at have a bulk material that isn't very soluble in unagitated, cold, pH 5, water. This is not a very good simulation for any part of the human digestive tract.

    I wish you lots of luck in your thesis.

  • I should add that til recently, I was taking omeprazole, which I believe can cause b12 problems.

  • It is well known that taking PPI's can prevent good absorption of B12. You probably had low acid so taking a PPI makes matters worse. You need good levels of acid in the stomach to break down proteins. PPI's have been a huge money spinner for Big Pharma and in many cases wrongly prescribed. They are intended as an 8 week or short course - but GP's often forget to mention this important point.

    One of our grandsons was recently prescribed this medication by a gastroenterologist and his parents were not told it was to be a short course. He no longer takes them.

    Forgot to mention if you do choose to take tablets then it may help to buy some lozenges of B12 that dissolve under the tongue - get absorbed into the micro-circulation - and thus avoid any stomach/gut issues. Jarrow Methylcobalamin from Amazon in 1000mcg or 5000.

  • I am curious if you think that ACV with the mother might be a good thing to try to increase the acid in the stomach and if it would aid in the absorption of the B12?

  • Not sure about that 😊 All I know from reading is that good acid levels are required to cleave the B12 molecules from food for the onward journey. B12 is metabolised in the Terminal Ileum - so if you have any gut issues then that is where absorption is impaired ....

  • petal02 ,

    The British National Formulary, not the home of any form of radical statement, says:

    Apart from dietary deficiency, all other causes of vitamin B12 deficiency are attributable to malabsorption. There is little place for the use of low-dose vitamin B12 orally and none for vitamin B12 intrinsic factor complexes given by mouth. Vitamin B12 in larger oral doses of 1–2 mg daily [unlicensed] may be effective.

    And yet the ONLY B12 tablets it lists are 50 microgram cyanocobalamin at what appears an extortionate price:

    Tablets, cyanocobalamin 50 micrograms. Net price 50-tab pack = £8.99

    If the above is what you have been prescribed, think carefully about why you might have low B12. Think how long it might take to raise your B12 to adequate levels at that low a dose. And realise that high dose (e.g. 1000 micrograms) can get into your bloodstream by diffusion - which allows even those who have major absorption problems potentially to raise their levels.

    You can purchase your own B12, get to choose whichever sort you want/need (cyanocobalamin, hydroxocobalamin or methylcobalamin) in whichever dose you wish (usually 500, 1000 or 5000) for what seem not too bad prices. The first I came across on UK Amazon (as an example):

    Jarrow Methylcobalamin B12, 1000mcg, 100 Lemon Flavour Vegan Lozenges

    Price: £6.95

    You also have options of various forms such as lozenges, nasal sprays, etc.

    I have to wonder if your doctor is either attributing your low B12 purely to diet - or humouring you. Of course, my suggestion that is what has been prescribed for you could be totally wrong, but at least you can then simply ignore me. :-)

  • Hi Rod, what is your opinion of effectiveness of Better You B12 Boost spray?

  • Afraid I know nothing of the product - or what people think of it. I hope someone with experience of it is able to answer more helpfully.

  • Helvella - that's really interesting, thank you. But if it is omeprazole that's caused the problem, how long does it take your body to recover? I took it for one month in March 2015, then Aug-Nov 2015.

  • I don't know is the only honest answer.

    If you levels had been nice and high, I suspect they would not have plummeted so far due to Omeprazole for a few months. So I suspect they were not that wonderful before.

    My view is that you really don't want to stay at the very low end for any longer than necessary. That means doing something a bit more significant than taking a 50 microgram supplement.

  • Sorry for the delay in coming back: I have been prescribed cyanocobalamin, taking 50mcg twice daily. Can anyone make sense of this?

  • Yes - it is the only one listed in BNF. Quite possibly the only one listed on your GP's computer system.

    But whether you take them or any other oral B12 supplement, your end-of-January test will reflect the taking of the supplement(s), not your effective real B12 levels. Which, by being a bit higher, will likely result in your being refused injections.

  • Can I suggest that you keep a detailed record of your symptoms along with food taken and present these to your doctor. There is a lot to work out - no sense in testing in the new year because the results will be skewed because of your supplements. Consider taking someone else with you to help convince the Dr you need more urgent treatment. It will be a long month for you!

    Good luck.

  • I think my doctor wanted to try the supplements in the first instance, to see if this would get me back into the normal range and and stop the symptoms, and then if this doesn't work, to start injections.

  • I'm on Jarrow 5000-7500 mcgs B12 methylcolbalamin sublingual a day. Plus a B-multi and Folate. It's been 3.5 months. The last 3 months were full of start-up effects of replenishing my B levels. This is to be fully expected if you are low, in fact it's how you will know that you need it. All of those deadened nerve endings spring back to life. I've had all of your symptoms and more. I am now starting in the last few weeks to feel great. Best that I have in years! You just have to hang in there and get through it, I found this blog indispensable for help!

  • Could I ask your startup symptoms? That's a struggle for me.

  • I think it would be better if the doctor would give you a trial of B12 injections as you're feeling so unwell and having to take other medication to deal with it. You would probably get better more quickly. Then you could try taking the tablets after that to see if they prevented the return of the symptoms.

  • Hi Petal,

    Has your GP ordered an IFA (Intrinsic Factor antibody) test? This is a test that can help diagnose PA (Pernicious anaemia). It is not always reliable though and it is still possible to have PA with a negative test result.

    I would be concerned that taking oral supplements without a firm diagnosis of the cause of your B12 deficiency might make it hard to get a diagnosis from NHS. Has your GP explained why she/he thinks you are deficient. I believe that oral tablets are sometimes recommended if there is a dietary cause to the deficiency. Does your GP think your B12 deficiency is diet related? Which as you are neither vegan nor vegetarian is hard to understand.

    Have you seen the "BCSH Cobalamin and Folate Guidelines" which came out in 2014?

    It's a long document but I read all of it and found it very useful. I gave a copy to my GP as some Gps are unaware of this document. I was told the NHS should be using this. Page 29 is a diagnosis flowchart which might help GPs.

    I have been ill for many years and failed to get a confirmed diagnosis although I am highly symptomatic for PA/B12 deficiency. I chose to self treat as an absolute last resort which has led to some improvement but self treatment has made it virtually impossible to get a diagnosis from NHSand i am faced with trying to afford B12 for the rest of my life.

    Other blood tests

    MMA, Homocysteine and Active B12 tests can help in the diagnosis of B12 deficiency. Taking supplements may affect the results of these. They are available privately if GP does not order them. A blood smear (aka blood film) can also help as it can show shape changes in blood cells that can occur if b12 deficiency is present.

    Have you had tests for ferritin, folate and a full blood count (FBC) as well as B12?

    High MCH and high MCV on the FBC can indicate the possibility of macrocytosis (enlarged red blood cells).

    Do you know your actual b12 result? I always get copies of my blood test results as I learnt from experience that what I was told over the phone or sometimes to my face was not always what was on the copies. I find it useful to track my results over a period of years.

    Useful websites/ documents/articles/books about B12


    01656 769467

    Office open between 8am and 2pm every day except Sundays

    I found PAS very helpful to talk to, if you leave a message they will get back to you wthin a few days.

    "Could It be B12" by Sally Pacholok and JJ. Stuart

    A very comprehensive book about B12 deficiency.

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

    Martyn Hooper is the chair of the PAS and has written several books about PA and B12 deficiency.

    Medicines and B12

    You mention you are taking stemetil. Some medicines can affect the uptake of B12 in the body. See link below.

    Nitrous Oxide

    Have you had any surgery involving nitrous oxide recently?

    I am not a medic just a patient who has struggled to get a diagnosis and wants people to have the info they need.

  • Very interesting bit on nitrous oxide. I saw my GP yesterday and suggested that my sudden crash may be due to my having had nitrous during my colonoscopy. Luckily, he'd read Martyn Hooper's book (what I gave him) and remembered that it could wipe out B12 levels.

  • Will compose new thread.

  • Hi Sosoosunnny,

    I'd suggest starting your own thread on the forum.

    Responses on old threads often get missed. You'll get more people answering if you start your own thread. It's helpful to know which country a person is in as patterns of B12 treatment vary from country to country.

    "I went and bought some b12 tablets"

    Supplementing without a diagnosis of B12 deficiency can make it very difficult to get a diagnosis.

    If you're in UK, I'd suggest reading

    BSH Cobalamin and Folate Guidelines

    BMJ B12 article

    B12 books

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

    Martyn Hooper is the chair of PAs (Pernicious Anaemia Society). Book is up to date with UK B12 guidelines.

    "Living with Pernicious Anaemia and Vitamin B12 Deficiency" by Martyn Hooper

    Has several case studies.

    "Could it Be B12; An Epidemic of Misdiagnoses" by Sally Pacholok and JJ. Stuart (USA authors)

    Very comprehensive book about B12 deficiency with lots of case studies.

    B12 websites (UK based)

    PAS (Pernicious Anaemia Society)


    PAS tel no +44 (0)1656 769 717 answerphone

    As you say you have all the symptoms of PA, might be worth joining PAS.

    B12 Deficiency Info

    I've written some very detailed responses in last few weeks so might be worth searching for these.

    I am not medically trained just someone who has struggled to get a diagnosis.

  • Once you start on injections of B12, it can feel like a roller coaster.

    There are new symptoms that show up right after the jab. Some super highs, some not.

    Then you feel normal for a while. Whatever normal feels like to you.

    Then the original symptoms start to return.

    Keep a log book as progress on healing neurological damage is slow. New pain symptoms or hunger indicate that the nerves are healing.

    Check also on any new food issues. Particularly gluten and dairy (casein protein).

  • This is an interesting read about risks of taking supplements (including sublinguals) instead of injections:


  • Hi, I am glad that you are starting to get some help and its interesting how often thyroid comes up with this problem.

    However how the symptoms are described reminded me of just before I was found to have low B12 - I remember talking to the lady at the chemist about how I was feeling and she took my blood pressure which she said was quite low. She looked at me and said - " do you feel away with the fairies?" And really that sort of summed it up in one for me :)

    All the best to you.

  • Hi, i have b12 deficiency (due to diet i believe as i am a vegetarian and haven't really eaten any b12 fortified foods in quite some years) my levels in my blood test were at 179, my main symptoms are psychosis tinnitus and some cognitive problems, I'm curious to know if raising my b12 levels help alleviate these symptoms and also if anyone knows how long it will take, my doctors put me on 50mcg cyanocobalamin tablets 2 to take a day, I've been having these symptoms for a year now and i hope it's not too late to reverse the damage

  • How long have you been on the b12? Don't despair, a lot of healing is possible.

    I think especially with neurological and cognitive symptoms, go with how you feel. If you notice improvement, make sure you get the treatment you need. Also do watch out for side effects.

  • My B12 levels were approx. 170 was I was diagnosed - I started taking the same supplements as you, and my levels were at 241 ten days later, but my symptoms were still quite bad so I had injections (6 in total, 3 per week for 2 weeks) to boost my levels quickly, and now I just take supplements. My doctor tested for intrinisic factor, and the results showed that I don't have an absorbency problem - I'm due to have another B12 blood test in a few months time, just to check everything is OK. But it took 4 of the 6 injections before I started to feel better; could you ask your doctor for injections, just to get your levels nice and high again, and then maintain them with supplements?

  • hi petal,

    I had a consultation over the phone with a doctor (not my usual one) and she's requested another blood test do be done, I did ask about injections but she brushed it off, after i get my bloods redone I'm going to make an appointment with the doctor that gives my nan B12 injections in the hope that she will comply, my original intent was to get my B12 nice and high from the injections then take a good multivitamin and B12 vitamin as supplementation.

  • I think you're right to see your nan's doctor - all the doctors at my practice seem to be up to speed about injections and their benefits, but I gather that's not always the case.

  • I've read loads lately that doctors aren't up to speed on B12 deficiency and from my experience I somewhat agree, last year when all these symptoms made their presence I went to my doctors, she did bloods (vitamins, thyroid etc) and they all came back normal but she didn't check my B12 and she diagnosed me with depression, it's a shame at that time that I didn't know what B12 was otherwise I would have asked, you mentioned your symptoms have improved, I imagine that's because of the injections, what symptoms did you have if you don't mind me asking?

  • Nathan12345 - just wondered which thyroid tests you had and what were the results ? When docs say normal - they often mean in range. Where they are in the range is key. Also they rarely do all the tests needed to diagnose a thyroid issue .....

  • My thyroid came back as low but my t3 and t4 were in range, t3 was in the higher end and t4 in the lower end but still in range (i cant remember the numbers sorry) so the dr i seen has dismissed it as a thyroid problem

  • You are entitled legally to have copies of your blood test results. Were your anti-bodies tested ?

  • Yeah my anti-bodies were tested and again they came back in the normal range

  • Unusual for the FT3 to be high in range and the FT4 to be low. Maybe check your copies.

  • It might have been the other way around, i cant remember but i know one was on the higher side and one on the lower

  • Both need to be in the upper part of the range. T4 is a storage hormone with very little to do. T3 is the ACTIVE hormone and needed in every cell of the body. When low things begin to go wrong ....

  • Thanks, will speak to the dr who ordered the blood test about it once she hears from the endocrinologist

  • Lets hope your doc is up to speed on Thyroid. Most go by the TSH alone and have little understanding of the workings of the thyroid. Low B12 and low thyroid often go hand in hand. Having been on the Thyroid Forum for 5 years I have learned a great deal 😊

  • My biggest problem (before getting injections) was feeling ridiculously faint and light-headed all the time. I had a couple of weeks where I felt too faint to drive, and couldn't cope with being on my feet (which is no good when you have to go to work). I then started getting ringing in my ears, and pins and needles in my right hand and foot. It was really unpleasant. I couldn't imagine ever feeling well again - but thankfully I'm fine now, and I intend to stay that way !!!

  • I've had the faintness feeling as well as feeling constantly dizzy, it has eased up quite a bit but some of the other symptoms seem to be lingering, it's great you're feeling better and just shows that there is hope, I've not felt myself for quite a few years as when I was in college I suffered with anxiety which seems to have come out of nowhere adapted my life to that and got hit with this out of the blue whilst working early last year. I'll definitely be supplementing from now on and consider this a lesson to be learnt!

  • I have been suffering with anxiety stress etc. I had two injections so far and couple of weeks of tablets. The recent test shows the level at 376. I would like to know how long it will take to raise the level to 800.

  • Hi Suresh just noticed this.

    Feeds on activity aren't one of HU's strong points so if you post something on an old post it is unlikely to be picked up - have just responded to your post on the anxiety forum

    Better to start a new post as you did there.

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