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Strange feelings after loading dose of B12

Marrob profile image

Just finished loading dose and having horrible symptoms! Bad headaches, head feels fuzzy, eyes blurry, very unsteady on my feet, so tired, muscle aches and palpitations! I thought I would feel a bit better but feeling a lot worse, is this normal! Thanks for any help!

18 Replies

Generally, loading dose means alternate day shots for at least two weeks. Is that what you had? Also, it's a good idea to mention what injection you took for example, hydroxycobalamine or cyenacobalamine etc. Also, what was the cause of B12 deficiency? Vegan diet, malabsorption, PA etc.

I am a vegan for 7 years, made a mistake of not taking B12 supplement. So far I have taken 7 shots so you can consider that as loading dose. I have observed a new pain in my left leg calf. Last evening while walking I experienced more swaying than usual and although this dizziness was the prominent symptom to investigate, last evening's dizziness was a bit scary. Today morning it wasn't so bad.

Marrob profile image
Marrob in reply to nkindia

Hi nkindia, Yes I’ve had six injection over two weeks and to have three monthly ones now! Hydroxycobalamine! I have a high output ileostomy which is the cause of B12 deficiency, I do not have the part of the bowel that absorbs B12. Last injection was last Monday but last night I felt awful, very sore muscles, off balance, felt something was going on in my head, horrible feeling! I had some neuropathic symptoms before the injections but never felt this bad, also I was at doc on Wednesday and my blood pressure was very high, 170/95. I’m waiting on a monitor!! It’s horrible not knowing if this is normal or if something else is going on! Having bloods done Wednesday so see what that turns up! Thanks for replying!

nkindia profile image
nkindia in reply to Marrob

The reason I wanted to know what kind of injection is because cyenacobalamine can cause high blood pressure but hydroxycobalamine raises bp only for a short time like 4 hrs, that's what I understood from web search because I am in the same boat. Doc has given me bp medication. Did you check your homosystine level? In B12 deficiency it may go up and cause these problems. Let's hope things get better for us.

Foggyme profile image
FoggymeAdministrator in reply to nkindia

nkindia. I’ve never heard of or read any research which indicates that any form of cobalamin raises blood pressure following an injection (excepting when B12 is given in high dose IV form (for cyanide poisoning) with additional fluids - and it’s the additional fluids that cause the rise in blood pressure, not the vitamin B12). In fact, B12 injection’s contribute to the lowering of blood pressure.

Are you able to give references for your source?

Worth noting that the web is rife with wildly inaccurate information about B12 deficiency (and it’s treatment) 😉

nkindia profile image
nkindia in reply to Foggyme

It says if your B12 is high ( because of injections) then it complicates the issue if blood pressure.

Foggyme profile image
FoggymeAdministrator in reply to nkindia


This site is primarily selling services and products (i.e. blood tests, vitamin 'push' bags etc.). It's to do with nutrition and 'cosmetic' type information and sales rather than with the presentation of accurate medical information - in particular how vitamin B12 pertains to those with absorption issues due to pernicious anaemia (and other causes) and it's treatment.

The information given is, in places, confused and reductive...or downright wrong. For instance, they make the incorrect assumption that both high B12 levels from injections and high B12 levels caused by underlying health issues can be damaging, failing to clarify that where B12 levels are high without supplementation, it’s the underlying health issue that is the damaging 'cause' - not the high B12 levels (these are simply an indicator that something is wrong, somewhere else (if you get what I mean). And high B12 levels following injections for B12 deficiency caused by absorption issues are to be expected...and are not damaging or dangerous. The best way to put this is that there's enough information to make it 'appear' credible...but dig down to the detail and medical veracity and credibility...disappears!

For instance:

High B12 from injections does not complicate the issue of blood pressure BUT an underlying health condition that causes high B12 (without supplements or injections) can cause high blood pressure...

AND there are certain medical conditions that require the cautious use of vitamin B12 (I.e. where stents are in place or where there is an underlying cardiac condition - but this does not mean that that having B12 injections (and pushing B12 levels up) complicates blood pressure - it’s the underlying heart condition / health issue that does that!

The overall message given by this site is that high levels of B12 can be dangerous...even from injections...and that any form of supplements should be stopped to keep levels within the reference range. Whilst this may be applicable for anyone with a dietary's a positively dangerous message for anyone suffering from a B12 absorption problem (only one of the causes being PA). This perpetuates the myth entertained by many doctors (that B12 levels must be within normal limits) to the detriment of those with PA. Doctors often stop injections on this basis. However, once injections have commenced, serum B12 levels are meaningless (they will always be high) and stopping injections (or other forms of supplementation) on this basis can result in the return of symptoms (and a severe reduction in quality of life) or worse, the progression of neurological damage (ultimately to death (the pernicious bit) if B12 injections continue to be withheld. Shocking - but it has and does happen.

So hence this distinction between the different approaches to treatment for those with a dietary 'nutritional' deficiency (where it is sufficient simply to raise B12 levels to within 'normal' levels) and to those with absorption problems (where levels of B12 are meaningless and are inevitably high due to injections) and where the requirement is to keep symptoms at bay - with however much B12 is necessary to achieve that.

I can't find anywhere on this website that suggests, as you say, that hydroxocobalamin injection’s 'raise BP for a short 4 hours'. And as per my previous reply, never come across this in medical literature or research papers.

I think the problem here is that many website (especially ones to do with health and nutrition or especially those selling products or services) don't quite get it right - and often get it very wrong - when it comes to vitamin B12, vitamin B12 deficiency...and most especially vitamin B12 deficiency due to absorption problems, one of which is pernicious anaemia (there are others too).

In this context (nutritional B12 deficiency v absorption issue B12 deficiency), a good way to ascertain whether a website is likely to present credible and medically 'sound' information is to look at the bottom of the page and see if the material presented is referenced to external sources (peer reviewed research papers published in medical journals etc.). If not, then the information on the website is most likely to be sketchy, inaccurate...or biased in a particular way...often because they’re trying to sell you something.

There are some PAS pinned posts to the right of this page when you log on - these speak to PA and vitamin B12 deficiency from a medical perspective (rather than to B12 deficiency from nutritional causes). Well worth a read and the information presented is accurate and pertinent to this forum. Also worth looking at the Pernicious anaemia website for reliable information about pernicious anaemia, it's diagnosis and treatment.


It sounds to me like you are probably short of magnesium.

The processes that use B12 need a wide range of vitamins and minerals to work properly and when you get enough B12 to repair damage, a lot of other things get used up. If they are in short supply you can get deficiency symptoms of these.

You will probably find benefit from taking a broad spectrum multivitamin and mineral supplement plus extra folate, potassium, magnesium and maybe iron and vitamin D - ideally from your food but you may need to supplement too if you are very low.

You can look these up online to find out the effects of deficiency and excess and what good foods sources you will like to eat and drink.

I'm sorry, I'm not feeling well from non B12 problems but if you'd like more information you could go to my profile by double clicking on my name and look under the heading "replies".

Hope you feeling better soon.

Thank you - and you! xx

Hi deniseinmikden, I had a year of having to have magnesium infusions after a bowel op which left me with an ileostomy! The B12 deficiency was inevitable but I am having bloods done on Wednesday so hopefully the results will show a drop in magnesium or anything else for that matter! I just expected to feel a bit better after the loading dose but it’s obviously not always the case! Thanks for replying, I hope you are feeling not too bad today! X

Yes i got worse before better. Keep going it will improve . Take your supplements. Drink lots of water and let the b12 injections do the work of repair. T C

Marrob profile image
Marrob in reply to Nackapan

Hi Nackapan, my problem is I have a high output ileostomy so I can’t drink water it just makes the output worse and supplements in tablet form just go straight through me, anything I need has to be by infusion! I’m hoping all these symptoms settle down so I’ll take your advice and give the injections time to work! Look after yourself, you’re having a rough time yourself x

Oh okay sorry I didn't understand what sort of ileostomy .I know someone with an ileostomy who can drink and eat.

Like you say if you find something to correct from your bloods that will help you too.

Thankyou, yes am struggling again

The early dark evenings a real problem as artificisl lights set my head off!

I hope your symptoms settle soon and you feel the benefits from your b12.

Marrob profile image
Marrob in reply to Nackapan

No apologies necessary, we are all so different, you were just trying to help! Yes the dark nights don’t help, look after yourself, any help from yourself is very welcome x

Between my second and third shot I had an insane 12-24 hours (obviously I have blocked out the memory!)

Every 10-20 minutes it felt like someone was shooting me with intense pain via an electrical shot. I was not without nerve pain in my head before the diagnosis, in fact my GP thought I had trigeminal neuralgia.

The pain and sensations were so intense that I had to walk around constantly. It did not allow me to sit still or lay down and certainly not sleep.

I thought about getting medical attention as I did wonder if I was having heart issues in the moment not knowing what that would feel like (and would not want anyone to assume about their symtoms and not reach out either). But I didn't. It left as abruptly as it came. I did take two magnesium tablets but I find it difficult to think that instantly stopped it. But who knows.

I suspect it was my body refiguring itself. Might be a coincidence but a boatload of b12 deficiency symptoms disappeared that night and have not returned. I am early - about a month in - so time will tell but it is what I believe.

So yes some of us feel worse before it all changes.

All the best to you. Hope you have relief soon.

Foggyme profile image

Marrob. If you had macrocytic anaemia prior to commencing you injections, it may be that you now have low potassium, which could account for some of your symptoms (you can look up the symptoms of low potassium via web searches).

In the presence of macrocytic anaemia, the body uses up extra potassium to make new red blood cells - this is a temporary effect of treatment and the body stops using extra potassium one the macrocytic anaemia has resolved and the production of red blood cells returns to the usual rate.

Try introducing high potassium foods to your diet - it may help (again, information on the web about high potassium foods).

If your symptoms continue, ask your GP to test your potassium levels to rule this in or out as a cause (this should be done in the presence of macrocytic anaemia once B12 injections commence - but most GP's don't do it)!

Even if you didn't have macrocytic anaemia (large red blood cells) increasing potassium intake via diet will do you no harm. Also worth noting that potassium tablets should never be take as a supplement unless under direct medical supervision (supplementing in this way can be dangerous and cause issues with the heart).

Hope you begin to feel better soon - it's often the case that once treatment with injections starts, things appear to get worse before they get better.

Good luck xx

Litatamon profile image
Litatamon in reply to Foggyme


Was just coming back to post that many of your symptoms Marrob align with low potassium. I don't remember if it was here or not but I read about someone changing their issues with injections by eating something with potassium before and after the shot.

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