Pernicious Anaemia Society
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Reaction to injections and tablets

Hi, I'm really not sure what to do. I've had blood test which shows my b12 is really low, dr called me in for injections. On the day after first injection felt really odd with strange weak sensation in legs, same for second injection. After the third injection I felt dreadful with a heart rate of 150 temperature and the same weak feeling in legs. My gp (and I) felt sure that the injections had caused this and she said she would definitely advise against any more. She gave me a prescription for high dose b12 tablets. To cut a long story short I have tried these and then sublingual tabs that have had exactly the same effect. Making me feel really ill with same symptoms for days I really am at a loss what to do. I cannot describe how Ill these have made me feel. If anybody has any ideas or similar experiences I would be really interested to hear. I am terrified to try again with the b12 but know it has to be treated. My gp has no ideas but is really sympathetic.

34 Replies

a) check what other ingredients are in the tablets/injections that you have been given and see if anything other than the B12 itself is the cause of the problem

b) check what forms of B12 you have been given - believe clivealive had problems with hydroxocobalamin injections and has to be treated with cyanocobalamin. Also some people have reported problems with high dose methyl. People do respond quite differently to different types of B12

c) try taking smaller doses to see if that kicks of the reaction - may be start off with .25mcg - that would be a quarter of the normal loading dose.

Some people respond to high levels of B12 in their blood by trying to shut down the mechanisms that facilitate it getting through to cells ... and that could be what is going on - which would imply lower doses might avoid the problem ... though reality is that the levels in your blood are now likely to be really, really high so it would be about avoiding getting to the point where levels kick off the response that leads to a functional B12 deficiency.

Have to admit though that the only things I've found in the literature - and my own experience - with functional B12 deficiency is that it tends to be about keeping levels so high that there is so much in the blood that enough manages to get through to the cells despite the response. However, B12 is a very individual thing and some people have reported that lower doses, potentially more frequently, work much better for them so possible that for some it is about keeping the levels in the blood below the level that triggers the response ...

This is link to an article on functional B12 deficiency - references a study in Denmark that showed that something like 40% of patients recieving B12 shots showed signs of functional B12 deficiency - lots in blood but non getting through to the cells

Inclined to think though that you might be best off trying to contact one of the following and see what they say - you would probably need to join PAS to get that sort of advice - though membership isn't astronomic ... and at you would probably need to ask to be put in contact with Dr Chandy.


Your doctor might find it useful to look at the first as there is a section there for health professionals.


Thanks so much for your reply. I have joined pas and have spoken to Martin on the help line who was very nice but could not come up with any ideas. I did email dr chandry who replied that b12 was natural and didn't cause any problems in his experience. My last attempt at taking any b12 was on Tuesday when I tried a quarter dose of the Holland and Barratt boost spray and again had a really horrible effect, temperature plus really fast heart rate and again the really weak legs that I still have today. I'm usually pretty stoic about stuff and pretty laid back but this makes me feel so bad that it is really frightening. I will look into the info you have sent me but if you have any more ideas I would be really grateful.

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sorry to hear that even the quarter dose proved to much. Frodo makes a good point about other minerals and vitamins. If you have macrocytosis then there is a real risk that your potassium levels can become depleted as the potassium is used up in processing the B12 - so it might be worth looking at that with your GP -

this is a link to the symptoms of potassium levels being low

muscle weakness,

muscle aches,

muscle cramps, and

heart palpitations (irregular heartbeats).

which sounds pretty much like what you are describing.

Another possibility is that the immune system is getting the B12 that it needs now and has gone into overdrive fighting an infection - and a lot of the symptoms we associate with feeling ill are actually the body fighting off the infection. Possible that the two are starting to combine.

Never been through this myself but can imagine it is really scary - my experience with the immune system was when I started to treat myself with large doses of B12 and was a few days in and started to really express a cold - runny nose and the works that I hadn't had for years - and I was using nasal spray as delivery method :).

Unfortunately anxiety is also a symptom of B12 deficiency and think that is one that can be a viscious circle - the more anxious you are the faster it depletes B12.

Would be good to establish

a) exactly what your levels were before treatment

b) look at your levels of various minerals after an injection/supplementation - though quite difficult now that everything has spooked you so may not be possible

c) establish exactly what symptoms you really do have - use the checklist on the PAS website - and GP may not be aware of a number of the symptoms and areas

All I can really suggest is trying really reduced levels of B12 and building up - may be even start with the supplement levels that would be used to treat a dietary deficiency rather than ones that would be used to treat an absorption based deficiency and see if there are any responses - look at potassium as a possibility with GP.

If you have had 3 loading shots then actually that might be enough for the moment but if your problem is absorption then you will need more at some point - and would be good to sort out that sooner rather than finding yourself going through all of this again.


Sorry had to rush out but didn't want to lose the post -

in saying 'spooked' I really don't want to belittle the way you are feeling or why. It's a very understandable reaction to something extremely concrete in this instance.

Also, like others wanted to emphasise that I am not medically qualified - just someone that works from my own experience and is prepared to experiment within safe boundaries. Your GP may also be prepared to experiment but has some professional boundaries on safe that are likely to be much more restrictive than those I have as an individual - the medical profession seems to be particularly adverse to anything that smacks of experimentation - the experiences of Dr Chandy for one show that the potential consequences can be rather unpleasant.

Keep posting.


We can't give medical advice here, but I think I've read that very, very rarely, there are people who have an allergic or extreme reaction.

Also, from posts on here, I've gathered there are people occasionally who have a fairly extreme reaction if they are low in other essential nutrients or have other conditions (possibly undiagnosed). People usually need to take folate (folic acid) as well as B12 for example. People also say they tend to take a multi vitamin/mineral supplement too and need to make sure all their other B vitamins are adequately supplemented.

Do you know why your B12 is low? If you are able to absorb it from food you could at least look into which foods have most B12, such as fish, and up your intake.

How do you get on with multi vitamins? There's one called 'Floradix' for example which is easy to absorb because it's a liquid and is derived from food sources and herbs. There isn't much B12 in it but if you can tolerate it, it might be better than nothing. It has wheat germ in it so you'd have to avoid if you were gluten intolerant.

If Martin and Dr Chandy don't know what's going on, I agree that is a bit difficult as they are the experts.


Hi KathyN

I'm not a medically trained person but am interested to know why your B12 level was "really low" There are many reasons why this can be caused for example are you vegan/vegetarian, had gastric surgery, take a contraceptive pill, Metformin or PP.I. such as Lansoprazole etc., I'm guessing you've not been diagnosed with P.A....?

Do you take part in extreme sports or exercises? Are you under a lot of stress in your daily life? As these too use up B12

What symptoms were you having before you started the injections and how long have you been deficient? Are any of the current symptoms the same or are they all "new"?

Could it be that the B12 is actually working at repairing the damage to your nervous system?

Some people have likened the effect of B12D on the nervous system to that of electric cables where the insulation has been damaged so the current is leaking away instead of getting through to the lightbulb.

Injections of B12 start to repair the outer sheath (insulation) of the damaged nerves (cables) and all of a sudden the "lights come on" in the brain as it starts to receive messages (current) from places previously not in touch with for a long time.

Another simile is that of a badly tuned radio that you (the brain) has to strain to listen to even with the volume turned up high when all of a sudden the signal (B12) gets "tuned" in and the result is painfully deafening.

As I've said I'm not a medically trained person but hopefully someone on here will be able to give you the advice you need.

I wish you well.


Hi, I am pretty much repeating what Gambit62 said, but what forms of B12 have you tried? Were the injections hydroxocobalamin or Cyanocobalamin?

I have tried 3 types, Cyano, injected, which I tolerated fine but it did nothing for symptoms, adenosyl cobalamin which, with only a few drops in a sublingual liquid form gave me a headache and fatigue and an unwell feeling. I inject methyl and am fine. So different forms affect individuals very differently.

Also, I take a food based multi vitamin and a B Complex from Garden of Life vitamins called Vitamin Code. You can get them from Amazon or other online discount vitamin websites. I use Swanson vitamins. You might find that you might tolerate these as they are food based? They contain methylcobalamin.

Please keep us posted. I am so sorry to hear of your reaction- it sounds just awful. And frustrating.


Hi KathyN. Oh dear, how very awful and frightening for you!

I agree with everything said by Gambit62, Frodo, Clivealive and Ndodge - really good advice given and worth following up on it all.

As Frodo points out there are rare instances where some people have an adverse reaction to B12 injections!

If you type in 'patient information leaflet [and then the name of the particular cobalamin you have used] this will take you to the information about possible adverse reactions that may be occuring. Also, type in Mayo clinic adverse reactions to B12 and you can find more information there.

What you are experiencing could be for a variety of reasons and as B12 deficiency is such a complex issue, it might take some time to sort out what is really going on.

If you are having an adverse reaction to B12, then the following might be of interest.

I see you are a manner of the PAS. If you look in the library section, there are details of two doctors who specialise in treating patients who are allergic to B12. They 'desensitise' patients so that they can receive replacement therapy in the form of B12 injections.

What is clear is that if you have low B12 (for whatever reason) then you do need to be able to have some form of replacement therapy. Perhaps you could discuss with your GP with a view to getting a referral to either of the following:

Prof. tak H Lee and Dr Pierre Daguerre, both at Guy's Hospital in London. The full address and email contact details are on the PAS website in the library section so you could always email them to ask what your GP needs to do to get a referral?

The fact that your GP is really sympathetic is really good news (many are not) and should help with his willingness to make the referral, if needed.

I'm currently having trouble with B12 (though my reaction is not as severe as yours) and am seeing a neurologist who may or may not get to the bottom of the issue. If I find out any further information that might help, I'll let you know (though this might take some time - the wheels of the NHS grind slow!).

Good luck and please post again to let us know how you are doing xx


Excellent post, foggyme! So helpful! I'm sorry to hear you are having problems now. Hope it all resolves for you. My very best wishes for you. :-)

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Oh thank you Ndodge 😊. It's all part of the rich tapestry called B12 deficiency! I'm going to sew my way back to health, one stitch at a time - with a few little pricks along the way!

Hope you're doing okay 'over the pond' and please don't forget to let me know if you'd like to try the hydroxo.

Take care xx

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Hi foggyme, just woke up from a 3 hour evening nap. Time for more B12!

I found out that the local compounding pharmacy can make up hydro for me, but I am reluctant to try it because I took some adenosyl in sublingual liquid drops and after just 2 doses felt horrible. Headache, really fatigued, so once I remembered that hydro breaks down into methyl and Adeno, I am very reluctant to try it. The methyl works great for me and I have discovered that if I give myself 80% of a mg. every other day, I have more energy and the tinnitus consistently goes away for a longer period of time. Not until the next injection, but getting there.

I feel as if I've finally found the correct dosage and injection schedule and all has smoothed out.

Just have to resign myself to every other day shots but I am much more stabilized than before. So it is worth it. As the saying goes," if it ain't broke don't fix it!"

Thank you for thinking of me re: hydro, you are a cupcake! & a smart cookie! :-) xx

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Hi Ndodge. Three hour evening nap sounds just like me. Have to have a rest before I go to bed 😊.

Really pleased you're finding a regime that works for, probably right decision about the hydroxo.

Oh how I wish we had compounding pharmacies who would deal direct with us, here in the UK. It would truly be a miracle if we could go in and just order our cobalamins. 'Oh, think I'll have 20 shots of methyl, two of hydroxo, and a side of adenysol, for good measure' - it would be like Christmas and birthday all in one!

Anyway Ndodge, keep well and keep safe...hope your sister is doing okay 😀 xx


Hi Foggyme,

Sorry to take so long to get back to you! I wish that you had compounding pharmacies over there, too! But you can order from Germany and that is less expensive- the compounding pharmacies charge about 5.00 US dollars per injection whereas you pay about a dollar an injection. So, nothing about getting enough B12 is easy or cheap, for any of us! :(

My sister is doing much better, thank you. She is on a diazapam Rx - Klonapin- which she has avoided for years but finally had to give in. But she's so much better and they have stopped the panic in its tracks!

I hope that you start feeling better soon and figure out that neuropathy problem. I wish we could check our B12 levels like diabetics check their glucose levels. It is so hard to know whether to do more B12 or less. Especially as about 40% of us folks ( and I am starting to believe I am one of them!) develop an antibody to the B12, as Gambit 62 has pointed out.

Onward and upward! :)

Take care xx


Grief Ndodge...your B12 must cost you a fortune! And you're right, nothing about it is easy for any of us!

Pleased about your sister....hope this is the beginning of better times for her.

And I think I'm probably an antibody person too 😖😖.

Wouldn't it be good if there were people out there doing decent research and doctor's who were interested enough to help us through this dastardly thing!

Truly don't know how I'd be getting on without all my 'stranger friends' here 😀😀.

Be well xx

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I second that emotion!

It is so hard to duplicate what the body does (or should do) naturally. There are probably so many variables to this B12

problem that we are stabbing in the dark to figure it out for ourselves. (Ha ha pun intended!)

Yes, there needs to be in depth research, just like there is with diabetes.

Wouldn't that be a dream come true!

Well, here's to dreaming! :-)

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I'll third you in that!

Exciting here.... delivery of my second grandchild in progress!


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Oh, my gosh, congratulations !!

Please keep us posted about the baby- I'm so happy for you!

:-) xx

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Hi. There is a compounding pharmacy in Glasgow that works with doctors and posts out drugs. I'll look up the name. I found out through the low dose naltrexone web site.

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Hi there. My b12 was also really low and within a few days of loading doses I got feelings of extreme heat buliding in my body, a racing heart and pain in my left hand and foot.Weird sore tingling feeling for last few months I self inject every 4 days with hydrochobalim(,sorry about spelling) and feel better.My brain fog,extreme tiredness has improved and the pain in my finges has lightened but if i go more tham 4 days it deteriorates again I think pain is nerves waking up .Also add multi b vitiman and try to add magnesium (zero capsules dissolve in water are great) This is just my journey and have found these of benefit so maybe something here can help.wishing you improvements. ☺linda


As well as cyanocobalamin, hydroxycobalamin, methylcobalamin there is also adenosylcobalamin. Some people respond better than others to a particular form of B12.

I wondered about your folate and iron levels as i have read that both folate and iron levels need to be good in order for B12 to be taken up effectively by the body.

I also wondered if you had had your potassium levels checked recently as I have also read that a drop in potassium can happen when people start to supplement B12.

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


Thanks so much to everyone for all the responses, so much appreciated and all taken on board. I am seeing my gp on Tuesday so can go through some of the stuff with her then. Certainly the potassium thing had occurred to me and I have been trying to include more of this in my diet. My b12 deficiency seems to be due to being on the ppi omeprazole for 14yrs and it was because of my concerns about this that I went to the doctors in the first place and why she did the blood tests. I really knew nothing of b12 deficiency before this just that problems with long term ppi use had come to light. I have tried on many occasions to come of the drug but to no avail and my doctor had said not to be concerned at that time. I will check exact results on Tuesday, apparently my vitamin d was very low as well. All the symptoms I have had since the injections have been new. In retrospect I think I have had a lot of b12 deficiency symptoms for a long time for example extreme tiredness which luckily I've been able to manage as I work for myself and am able to pace myself, also tinnitus and I can so well relate to the brain fog thing!


Just a thought about PPI's ....(which I was on for several years).

Turns out that low stomach acid has the same symptoms as high stomach acid...what I actually had was low stomach acid and the PPI's were just making it worse by reducing my stomach acid even more. Ended up on ever higher doses which never 'cured' the symptoms, just made them worse, resulting in my thinking I couldn't stop taking them!

The acid reflux eventually disappeared once I had been off them for several months.

May not apply to you but worth a thought.

Good luck the doctor on Tuesday. Please let us know how it goes.



Some links that might be of interest.

Not sure it will help with your current problems but I found reading "BCSH Cobalamin and Folate Guidelines" helpful.

B12 books

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

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

Found this old HU thread that might be of interest

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Hi, again thanks so much for all the information links etc, all so helpful. Have been back to my gp today. My b12 was 85 before the injections my potassium was within normal limits. She took the potassium being depleted after processing b12 thing on board and took bloods for that and repeated b12 test also thyroid . She has no real ideas but agrees that I shouldn't take any type of b12 for the time being. She has referred me to a gastroenterologist. I know I was really lucky to not feel too bad before the b12 jabs but still a week later after my last b12 tab feel really rough with all the same symptoms. Thanks to foggyme for comments on ppis I completely agree and am still trying to come off them but have had major reflux probs since a child and my life before omeprazole was awful so it's really difficult. Thanks so much again guys!


Hi, have you ever been tested for food allergies and coeliac? I have both and since I've removed all the trigger foods I have no pain or reflux. Worth a thought.

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Hi KathyN. I've just been reading (today, in fact) about gastric reflex problems. If PPI's are not working, other causes of reflux can be achalasia (the gullet loses it ability to move food along due to problems with the nerves in its walls), problems with the way stomach values work, bile acid escaping from the duodenum into the stomach and oesophagus (because of muscle problems) and slow gastric motility / gastric paresis. And there's probably more.

There's a test called Esophageal Manometry which measures the force, coordination and movements of these muscles. Apparently, it's available on the NHS but is quite specialised and not done at every hospital.

If you've had reflux problems since childhood, it might be worth thinking of looking for other causes and the above test might be useful if you can find somewhere to get it done.

Really pleased that your appointment went well but can I just add a word of caution...your B12 is very low and if your symptoms are due to B12 deficiency (which would be likely with such a low level), rather than an adverse reaction to B12 injections, then it is not a good idea to go too long before supplementing with B12. Particularly if you have neurological symptoms. These may become irreversible it you do not get sufficient B12 in the early stages. Your GP may not know this.

Whist the reflux is horrid and painful and obviously wants 'fixing', it's the B12 deficiency that has the potential to cause most long-term damage to your health.

Really sorry....I'm not trying to frighten you or 'rain on your parade'...I (like many others here) received insufficient B12 in the early stages and it's now looking likely that I do have some irreversible damage.

My GP had no knowledge of B12 deficiency, particularly in relation to the potential for long-term irreversible neurological damage. Many GP's are ill informed and though some are well meaning, unnecessary damage is being done to patients.

And please be aware that many gastroenterologists have little knowledge of B12 deficiency either, so you may have to become your own expert.

If you want more information about B12 deficiency, a site well worth looking at is and, of course, the PAS website.

Anyway KathyN, hope you get to see a gastroenterologist very soon and please do pop back if you need more help. It'd also be really good to hear how you get on.

Take care xx

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Are you taking Methylcobalamin or Cyanocobalamin. Sublingual Methylcobalamin bypasses the stomach and goes directly to the brain and nervous system.


The injection was methyl cobalamin I believe. Got blood results today apparently my thyroid is under active and starting treatment for that potassium fine. Thanks so much for all the interest, sorry I'm not replying to individual posts, I just feel so rubbish that it's a bit of an effort at the mo. Can anybody relate to A really weak feeling in the legs that's my main symptom at mo and I find it a bit scary to say the least.

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Hello KathyN. legs are like rubber and so weak I now have trouble going for anything but a shortish stroll (up until three months ago, I was walking at least five miles a day). Walking upstairs is a bit of a tease!

It is scary, isn't it 😖

Please that they've identified your underactive thyroid. Rubbish at thyroid stuff but treatment for that will hopefully make you feel a lot better.

With so much going on at once, it's not surprising that you feel so bad....don't despair...perhaps it's a case of being at rock bottom and Inge can only get better 😀

Take care. Hope you feel better soon xx


Hi Joycekay. It's really not quite that simple - but how I wish it was 😀.

Any of the cobalamins (Hydroxocobalamin, Methylcobalamin, cyanocobalamin or adenosylcobalamin) taken sublingually (lozenges or sprays) or via nose drops/sprays or transdermal patches, enters directly into the blood stream, thus bypassing the stomach. This is a good thing since anybody with PA cannot absorb B12 from the stomach and most people with B12 deficiency can't either.

At a most basic level, once in the blood stream (and hence the cells) the B12 (whatever the form) is transported to all areas of the body. (Some people have problems with B12 at a cell level, but that's a different story).

Some people find that for them, sublinguals, sprays, drops and patches just do not work.

Some schools of thought think the Methylcobalamin is most effective for neurological symptoms (perhaps this is what you have found) but not everybody finds this. Some do better on Hydroxocobalamin and clivealive has been taking cyanocobalamin successfully for more years than I care to think of!

So....the cobalamins (and the different delivery methods) tend to work differently on each individual that uses them. What works for one doesn't always work for another. For most, it's a case of finding out out what works, for them, and sticking to it.

Apologies for the 'splurge' of information (which you probably know anyway) but thought it a good idea to expand for anybody new who may be searching for information.

Hope the methyl is working for you 😀😀

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Poor you that's dreadful, do hope things improve for you soon. What I find so confusing is that all these symptoms came on after my b12 injections which I only had after testing levels because I was on omeprazole. I suppose I had a few vague symptoms but nothing that I would have gone to the dr for.

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Yes...its is confusing isn't it. I've read many posts about this and lots of knowledgable people suggest that it may be down to the 'repair' process where things a healing and 'waking up'. This makes a lot of sense to me and after I was diagnosed, I realised that I had lots of symptoms that I'd just brushed off got so used to that I thought they were normal! Or I attributed to getting older (though 56 to 90 is a bit extreme). I also had things that had been misdiagnosed (I.e. Morton's neuroma) that were more likely due to the B12 deficiency.

It's really good news that you didn't have too many symptoms before being diagnosed since if you get enough B12 early enough, the chances of a good recovery are vastly increased.

So don't despair, the chances are that you're going in the right direction 😀



Hi KathyN

I am having very similar effects after injecting B12. I feel awful for about 24hrs with hot flushes and racing heart and general feeling of anxiety.

I am currently having weekly injections as they have been effective in treating my symptoms but I have to put up with feeling awful for at least one to two days per week.

I am currently trying to up my potassium levels as this was suggested by other members of this forum. I have tried injecting a half dose one day and the other half the next ... Not sure if this is helping yet as just had it this morning but to be honest I'm already feeling fluttery and a bit hot. I also had the same result when I tried a high dose lozenge.

Between a rock and a hard place and not sure what to do next although I have a Gp that does listen I'm not sure he really understands much about it all.

If you have any updates I'd very much be interested to hear about it

Best wishes

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Hi julie74 Yes we're both having really strange reactions aren't we. I'm still really struggling. I just had the original 3 injections which just made me feel worse with each one and have since tried several different sprays, lozenges and tabllets which have all made me feel dreadful. My symptoms are really fast pulse, hot really weak feeling in arms and legs and just the last week pins and needles in my right leg. I have now got to the stage that even a multivitamin bring on these symptoms, I have no idea what to do and neither has my doctor. If any one has any ideas out there Ian sure we would both be really grateful. x


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