Pernicious Anaemia Society

Too much b12

I was on 6 weekly hydro injections from doctor which wasn't sufficient. Eventually through help on this forum i purchased my own ampules from Amazon Germany. I am finding I am needing at least 1 per week and often 2. My friend who is a nurse and has seen me suffer in the past years and done my injection after 2 weeks for me is worried now that I am doing it too much. I have convinced her you can't overdose on b12 as it is ex created out of your body. But because of her profession she is still concerned. I also use patches with folic acid as well as taking soluble forms as well. Health wise I feel better than ever but still have days were I dip. Can I get reassurance that u can't have too much b12 and I am not harming myself. Advice and opinions are welcome please. Thank you all x

20 Replies

Hi littlecarol,

Don't worry you can't overdose, all the B vitamins are water soluble so you can't overdose it's just excreted. It's used in extremely high doses to treat cyanide poisoning. I was taking 10x5000mcg of b12 daily, so 50,000mcg and I'm still here! I self inject every other day now and still use 3 or 4 lozenges every day.

I'm sure the experts on here will direct you to the relevant documents that will support that and you could give them to the disbelieving nurse. So don't worry. :-)


Little carol -honestly you cannot overdose on B12. I can't remember the reference you need to read the Dutch report on this or the European Union report on this But someone will let you know . The medical profession seems entirely ignorant on this subject in the UK . Carry on and inject without worrying . If it bothers your nurse friend so much ,I would get her to show you how to self-inject into your thigh. (Outer middle third to get the muscle) Best wishes


Hi my doc said to much b12 can have toxic effects. I to self administrator once a month and feel a little more human however I have my bad days and wonder if I should increase. I don't know what to believe.


Your doctor is wrong about that . There are scientific papers proving that B12 isn't toxic even in huge quantities (Dutch Heath service and EU.reports)

I read somewhere that there there is a condition where people with a certain liver disease have very elevated B12 readings . This is because of their liver problems . So these patients are ill because of that liver disease that's all . Increase your B12 injections without worrying . Best wishes ! PS ask someone to give you the links so you can read the reports I mention , I'm not very clever when it comes to things like that ! But I don't want you to be too worried to give yourself the injections that you need . The sooner the better . Delay can mean that you get irreversible problems -I know because my diagnosis was very delayed because of doctor's ignorance .


Hi Splodge1. My GP stopped my B12 in the mistaken belief that I had B12 toxicity! I emailed one of the research professors at a top UK university to ask if he could send me one of his research papers that I found on the Internet. He responded and said that there was NO SUCH THING as B12 toxicity and said that the high levels of B12 in my blood were simply an indication that treatment had taken place.

B12 cannot hurt you, only heal you. And many people have to inject Hugh quantities of B12 to be and stay well.

Since then I have been sent much information from people here and everything I have read confirms what he said.

What I actually needed was more B12!

Would be a good idea to follow Wedgewood's suggestion and learn to self inject. It's very very easy and people here can offer help about this, if needed.

Or maybe your friend who is a nurse will teach you?

Hope this sets your mind at rest.

Wishing you the very best of luck.

Pop back if you need more help or advice.


littlecarol I tried to reproduce the hyperlink here but I don't think it works so I've copied the whole article. Sorry it's a bit long.

The whole article reads as follows but if you just want to scroll down to the "Conclusion" I won't blame you:

"Treatment with high dose vitamin B12 been shown to be safe for more than 50 years

Out of fear of overdosing vitamin B12, treatment is often reduced to below the frequency that is needed by the patient, or, even worse, treatment is stopped completely.

As a result, symptoms can reoccur again and again and even become irreversible.

It is very clear this fear of overdosing is based on a misunderstanding. For over 60 years high dose vitamin B12 treatment has been used without any signs of the danger of an overdose.

The Dutch National Health Counsel and the Regional Disciplinary Medical Board of Eindhoven have stated clearly that vitamin B12 is non-toxic.

Clinical research and the treatment for cyanide poisoning have shown that even extremely high doses of vitamin B12 and the serum values that go with it are harmless.

A decennia long history of safe treatment

In 1926 it was discovered that patients with pernicious anaemia could be saved from a certain death by eating a pound of raw liver a day. More than 20 years later the substance that was responsible for that was isolated from liver extract: vitamin B12 or cobalamin. Since then numerous patients have been treated with high dose vitamin B12 worldwide. Usually per injection and often lifelong, as a deficiency is mostly caused by an irreversible absorption disorder. In all that time harmful effects have never been shown from overdose. No single case has been found in medical literature in the past 60 years.

No maximum dose

The Dutch National Health Council therefore decided not to determine a safe upper intake level for vitamin B12. In their report from 2003 “Voedingsnormen: vitamine B6, foliumzuur en vitamine B12” the council joined expert commissions from the American Institute of Medicine and the Scientific Committee for Human Food from the European Union, who had already reported 3 years earlier that toxicity from high dose vitamin B12 poses no real danger.1

Of course, like with any medical treatment, side effects can occur. Acne, eczema and itching seldom occur and very rarely anaphylactic shock. Changing brands of vitamin B12, forms of B12 (cyanocobalamin vs hydroxocobalamin), or switching from injections to tablets can be a solution in those (rare) cases.

Misunderstandings about blood and reference values

Yet often physicians reduce injections or even stop treatment altogether out of fear of overdosing B12. The result is that many patients are left with recurring or lasting symptoms, which could be relieved by more frequent injections. After an injection the serum B12 value rises quickly, well above the upper reference value (on average 150-700 pmol/L), followed by a slow decrease. Apparently the underlying thought is that it is necessary to keep the value between the (upper and lower) reference values. However the blood level of serum B12 rises regardless of therapeutic effectiveness.2

A high serum B12 value does not mean that symptoms are treated sufficiently. This presumption can have damaging effects for patients with neurological symptoms, which can become irreversible with insufficient treatment.

Treatment based on symptoms instead of blood values

The recommended treatment in the Netherlands consists of a hydroxocobalamin injection of 1mg every two months, after an initial loading dose of 10 injections in 5 to 10 weeks.3

No reference is made to the serum value or a danger of overdosing, unlike for instance in case of a vitamin D or A deficiency. The lack of danger of an overdose is further underlined by the advice to treat patients with neurological involvement with two injections a week for up to two years, if necessary. This also emphasizes that symptoms and not blood values should be used as a guideline. If serum values were decisive, even patients with neurological involvement could suffice with the maintenance dose of one injection every two months after the initial loading dose.

Elevated serum B12 values in serious conditions

Maybe the concern for a possible overdose is caused by the knowledge that some life-threatening diseases can be accompanied by a strong increase in the B12 blood value, in some cases to even 30 times the upper reference value.4

In blood diseases like leukemia, polycythemia vera and hypereosinophylic syndrome, the cause is often an enhanced production of the transport protein haptocorrin, to which most of the circulating B12 in blood is bound.

In liver diseases such as acute hepatitis, live cirrhosis and liver cancer, elevated B12 values are often found because the liver is no longer capable of storing vitamin B12.

Elevated B12 values are always cause for further testing, but of course, to the contrary, it cannot be concluded that elevated levels after B12 injections leads to serious disease.

Scientific research

Scientific literature offers numerous examples from which it can be concluded that treatment with high dose B12 up to very high serum values is no cause for concern.

In the treatment of children with an inborn error in the production of transcobalamin II, the binding protein that transports B12 to the cells, serum values are kept at levels of 10 000 pg/ml (about 7 400 pmol/L) without any side-effects.5

Japanese research from 1994 into the effects of B12 therapy in patients with multiple sclerosis shows that a daily tablet with 60 mg methylcobalamin during six months is non-toxic. Half of the patients even started with two weeks of daily 5 mg B12 injections straight into the blood. 6

In the fifties, when chemotherapy wasn’t available yet, children with neuroblastoma (a tumour of the autonomous nervous-system) received 1 mg B12 injections every other day during 2 to 3 years in a London children’s hospital. From 1957 the dose was adjusted to 1 mg per 7 kilograms of body-weight. In the majority of patients the tumour disappeared wholly or partially and the chance of survival was considerably increased.7

In 1999 in Japan, kidney dialysis patients with polyneuropathy, received 0.5 mg methylcobalamin 3 times a week intravenously for 6 months. Because of lack of renal clearance, serum values rose to more than a hundredfold from 422 pmol/L on average to 54 000 pmol/L, with 67 000 pmol/L as highest value, without side-effects. 8

Also in Japan, in 2007, patients with the incurable neurodegenerative disease ALS (Lou Gehrig’s disease) received daily injections with 25 mg methylcobalamin for 4 weeks, followed by daily injections of 50 mg intravenously, followed by 50 mg a week. In the long term, treated patients survived for longer because of this, than did untreated patients.9

Megadoses B12 as lifesaving antidote

The safety of vitamin B12 treatment is further illustrated by the decennia long use of hydroxocobalamin as an antidote for cyanide poisoning, often caused by smoke inhalation. In the Netherlands ambulances, fire departments and emergency rooms have the Cyanokit at their disposal. In life threatening situations 5 mg hydroxocobalamin is given intravenously within 15 minutes, an amount that corresponds with 5 000 injections of 1 mg B12.10 Hydroxocobalamin reacts in the body with cyanide, and forms cyanocobalamin, which is excreted in urine.

The serum value of B12 can rise to an average of 560 000 000 pmol/L within 50 minutes.11

If necessary this treatment is repeated within several hours, making the total dose 10 grams. The side effects that occur, like reddening of the skin and urine and changes in heart rate and blood pressure are temporary and harmless. In short: 10 000 injections a day are still not enough for an overdose of vitamin B12.

Regional Disciplinary Medical Board: vitamin B12 cannot be overdosed

In 2009, the Regional Disciplinary Medical Board in Eindhoven stated very clearly that an overdose is not possible: “There can be no question of an overdose of hydroxocobalamin, as the excess is excreted in urine by the kidneys and therefore cannot accumulate in the body.12 The Medical Board ruled against a patient who claimed his deteriorating health was due to the continued treatment with B12 injections. The patient received monthly injections for 10 years. The physician was not rebuked because the patient was treated according to guidelines.


A vitamin B12 deficiency can cause many different symptoms, among which are serious neurological problems. The treatment with high dose B12 injections is not only completely safe but fortunately also very effective. With the right treatment patients can recover completely. Starting straight away with treatment is essential, as is the continuing treatment in order to give the body enough B12 to fully recover. Therefore it is essential that patients are no longer exposed to the real danger of irreversible symptoms because of the imaginary fear of overdosing.


1. Voedingsnormen: vitamine B6, foliumzuur en vitamine B12. (Nutritional standards: vitamin B6, folic acid, vitamin B12) Gezondheidsraad.Publicatienr. 2003/04, Gezondheidsraad, (Dutch National Health Counsel) Den Haag 2003:130-31

2. How I treat cobalamin (vitamin B12) deficiency. Carmel R. Blood 2008;112: 2214-21

3. College voor Zorgverzekeringen. Farmacotherapeutisch Kompas. CVZ, (pharmaceutical reference book) Amstelveen 2011

4. De betekenis van een te hoge cobalamineconcentratie in het bloed. (the significance of a high cobalaminconcentration in blood) Ermens AAM, Vlasveld LTh, Van Marion-Kievit JA, Lensen CJPA, Lindemans J. NTvG 2002;146:459-64

5. Inherited disorders of folate and cobalamin transport and metabolism. FentonWA, Rosenblatt DS. In: Stanbury JB ea. (eds). Online Metabolic & Molecular Bases of Inherited Disease, The McGraw-Hill Companies,

New York 2001:3897-933

6. Vitamin B12 metabolism and massive-dose methyl vitamin B12 therapy in Japanese patients with multiple sclerosis. Kira J, Tobimatsu S, Goto I.Intern Med 1994;33(2):82-86

7. Neuroblastoma: an evaluation of its natural history and the effects of therapy, with particular reference to treatment by massive doses of vitamin B12. Bodian M. Arch Dis Child 1963;38(202):606–19

8. Intravenous methylcobalamin treatment for uremic and diabetic neuropathy in chronic hemodialysis patients. Kuwabara S, Nakazawa R, Azuma N, Suzuki M, Miyajima K, Fukutake T, Hattori T. Intern Med 1999;38(6):472-75

9. Clinical trials of ultra-high-dose methylcobalamin in ALS. Izumi Y, Kaji R. Brain Nerve 2007;59(10):1141-47

10. European Medicines Agency (EMEA). Europees openbaar beoordelingsrapport (EPAR) Cyanokit,Londen 2007

11. Hydroxocobalamin as a cyanide antidote: safety, efficacy and pharmacokinetics in heavily smoking normal volunteers. Forsyth JC, Mueller PD, Becker ChE, Osterloh J, Benowitz NL, Rumack BH, Hall AH. Clin Toxicol 1993;31:277-94

12. Regionaal Tuchtcollege voor de Gezondheidszorg te Eindhoven. (Regional Disciplinary Medical Board Eindhoven verdict) Uitspraak van 15 april 2009 nr. 113b Juni 2011

I've been on cyanocobalamin for 45 years and I'm still "clivealive" at 75 :)


Thank you for reproducing that clivealive, I really appreciate it. I was sitting in bed feeling fuzzy headed and lacklustre trying to motivate myself to get up and ready to meet a friend for a bike ride. I had been trying to hold out til next week before giving myself a si.

After reading the article I decided to just do it now. Feeling improved already!


It's obviously not just "Cycle-logical" then JanD236 :)


Excellent, Clive!


Hi littlecarol,

I self inject 3 times weekly but if I am stressed or my other autoimmune condition acts up, I have had to inject 4-5 x a week. I use 1mg. of methycobalamin in each injection. This is dosage is prescribed to me by my naturopathic physician. I, like LtAngua52, also use sublingual b12. I often take up to 15,000 mcg a day, on the days I don't inject.

I have never had a problem with these amounts and in fact would feel awful with many of my neurological symptoms returning, if I don't use this much.

I feel safe in suggesting to you to inject what you need to to feel good. Happy jabbing! :-)


Or as Fred Flintstone would say "Jabba Jabba do" NancyndodgeWilma...!


Thanks for the article - I have copied it into my laptop - and the dreadful puns!!!


Clive, I've been wracking my brain to try to top that one but having no luck! My husband can always tell when I am reading your puns because I laugh out loud. Keep up the good work- we all need some comic relief! :) xx


I have my injections prescribed for one every fortnight by my GP on the advice of a consultant neurologist which keeps my levels high (we aim for above 2000) so I wouldn't worry at all LittleCarol


Wow! you must have a really good GP nikkikent. I'm still stuck on 3 monthly injections and it barely keeps me going. As I've only been on treatment for 8 months I was hoping some of the symptoms that are still there are part of the healing process. I don't like the idea of SI but may have to go down that route if things don't improve. At 50 retirement isn't an option just yet!


I'm 54 and the NHS turned my pension request for early payment down. I have also worked in further education and not able to access that pension either - so like you - it's keep on working. If you live in the Kent area try for a referral to a Dr Munro at South Kent Hospitals NHS Trust.


People receiving B12 shots have slightly higher rates of cancer and tumour tend to be somewhat larger - however no causal link has ever been established. Its quite likely, as B12 deficiency is known to be a risk factor for cancer that the period of deficiency before treatment is the cause of the cancer and the fact that B12 supports cell reproduction means that it also promotes reproduction of the cancerous cells leading to larger tumours.

High levels of b12 in the blood can trigger problems that mean very little of this gets through to the cells where it is needed. One study in Denmark showed that this seemed to affect 40% of people receiving B12 shots. However, as the reaction is triggered by the rise caused by the initial injection ... Although there are some people who report that lower amounts of B12 more frequently work better for them the only things I've been able to find in the literature on treating a functional deficiency is actually more frequent shots - presumably putting so much in your blood that whatever is preventing it getting through to cells can't actually stop all of the B12 getting through.

see references in this document which is about the possiblity of using raised B12 to diagnose other potential problems

and this article on treating functional deficiency - just the abstract

Hydroxocobalamin is the treatment of choice in treating cyanide poisoning because there are no known issues with toxicity - the concerns about this method are around the fact that it is intravenous and involves pumping a significant amount of extra fluid into veins and can cause hypertension - so nothing to do with b12 itself - dose is 5g (ie 5000x the amount in a shot) administered over 15 minutes, followed by a second dose after 30 minutes.

There was a case in the netherlands a few years ago where a patient tried to sue a doctor claiming that B12 treatment had caused his poor health - the case was reviewed by their equivalent of the BMA and thrown out.


Thanks for the links, Gambit62, I have bookmarked them.

1 like

A massive thank you to everyone who took the time to respond to my concerns with their own experiences and documentation. I feel well equipped to reassure my nurse friend with this knowledge. She did teach me to self inject.... and has been a rock to me all the way through... so I am happy to provide her with the feedback I have received to stop her worrying...... thank goodness for this forum!! good health to all...


Thank u for your message. Yes I take folic acid tablets and use patches with methyl and folic acid too . I have suffered for many many years and now at last through self medication can feel normal again! I just listen to my body now and if I feel like I am dipping I can do something about it. Thanks for reassurance that it won't do any harm.

1 like

You may also like...