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The danger of taking too much vitamin B-12 -- bottle of vitamin B-12 with pills on the table spelling out 'B-12'


If your B-complex contains 50,000% of the Daily Value (DV), which is 6 mcg for adults, then it has 3,000 mcg of B-12. For people without a severe B-12 deficiency, this is much more than necessary. [Note: In 2016, the FDA lowered the Daily Value for B-12 to just 2.4 mcg for most adults, but this won't be reflected on all supplement labels until 2021. This means that your supplement actually provides 125,000% of the current daily requirement.]

Although no "Upper Tolerable Intake Level" has been established, there are risks associated with getting too much B-12 from supplements. At a dose of 500 mcg (one-sixth the amount in your supplement), an increased risk of colorectal cancer was reported in a placebo-controlled study of older people. Doses of just 20 mcg per day or higher have caused outbreaks of acne and rosacea. A high-dose B complex supplement (with 1,000 mcg of B-12) hurt, rather than helped, people with type 1 or type 2 diabetes and advanced kidney disease, resulting in a worsening of kidney function and an increase in the risk of heart attack, stroke and death.

In women who are pregnant, excessive blood levels of vitamin B-12 have been associated with an increased risk of autism in their children.

Taking some B-12 is advisable for people over the age of 50 (when you're less able to extract B-12 from food), as well as for those taking medications that interfere with B-12 absorption (such as Prevacid, Prilosec and metformin), strict vegetarians, alcohol and drug abusers, people recovering from surgery or burns, and those with bowel or pancreatic cancer. But the amount needed to avoid deficiency is small and nowhere near the amount in the supplement you describe in your B-complex.

If you decide to take a B-12 supplement, you may want to choose one that has the right dose for you and has been tested and Approved by Be aware that sublingual and dissolvable B-12 supplements often contain sugar substitutes that can cause gas, bloating, and diarrhea in some people -- particularly if taking multiple pills. You can use the Ingredients listings in CL's Review to spot and avoid these ingredients.

In general, it's best to avoid excessive doses of any vitamin if it is not needed.

Get more information, including the Recommended Daily Allowance for B-12 (by age and gender), differences in the forms of B-12, potential side-effects and drug interactions, plus's tests of popular products, in the B Vitamin Supplements Review >>

You can check the recommended intakes of other vitamins and minerals here.

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November 3, 2019

What about B12 in energy drinks? Is that the same as taking tablets or getting injections?
November 4, 2019

Hi Theresa - Yes, B-12 in an energy drink is the same as B-12 in a supplement -- so add that to your B-12 intake. A B-12 shot should also be counted. Be aware that energy drinks may contain far more vitamin B-12 than most people need, as discussed here:

December 18, 2018

I have, after months of searching on the internet and in stores, not yet found a B vitamin
supplement that is not grossly over strong. All appear to be approved by CL. What is going on??
December 27, 2018

Hi Nancy - The B vitamins that are Approved in our Review passed all of our tests of quality (contained their claimed amounts of ingredients, disintegrated properly, etc.) However, as you noted, and as we state in our Review, most B vitamin supplements tend to contain amounts far exceeding daily requirements, and some even exceed upper tolerable intake levels (ULs). To make this more clear, we've also noted in the results table, in green, how the amounts of individual B vitamins in each product compare to daily requirements.

Although it's difficult to find a B vitamin product that does not contain excessive amounts of B vitamins, we did identify one B complex that provides least 100% of the daily value for each B vitamin without exceeding ULs, and selected this as a Top Pick:

Another way to get a lower dose is to break a tablet in half, or choose a liquid product, since you can more easily reduce the dose -- such as our Top Pick for B12, which is a liquid:

July 2, 2017

In July 2016 my husband was diagnosed with Early Onset Alzheimer's. In August 2016 he started monthly B12 injections, since his vitamin B12 tested on the low end. I do not see any information about B12 injections, so I am wondering if having these injections gives too much B12 at one time?

December 8, 2016

I recently started talking a 1000 mcg dose of B-12. At the time I was on omeprazole (Prilosec) maintenance for a reflux condition. After about five days, I started to to get itching on my lower arms and neck.This occurred mostly in the evening. By day 6 the itching was very intense (read tear-my-skin-off itching). As I usually do, I considered what had changed in my diet and looked for possible side effects of B-12. Sure enough my situation was described and 50 mg of diphenhydramine was suggested to obtain relief. It worked in less than 30 minutes.

November 14, 2016

I have a rare disease associated with frequent RAS (recurrent aphthous stomatitis) and read B12 can help with that. Do you know about this and how much B12 if any would you recommend? Thanks
November 30, 2016
July 20, 2016

Male Age 78, reasonably good health, quite active, take a number of vitamins. I get very tired in the early afternoon ... Taking 5,000 B-12 sublingual MethylCobuline about 10 am makes a huge difference ... I can remain active into the evening. Normal sleep pattern is 9 pm to 5 am. Stopped B-12 and tiredness returned.... tested several cycles over several months with same results ( a few days off or on confirms efficacy) ... it works great for me. Wife 76 has same results.

January 4, 2017

I found that 300mg daily Niagen (similar to B3) quite effective in providing more energy. It produces NAD+ which is part of the mitochondria energy cycle.
January 4, 2017

Hi David - Thank you for sharing your experience. You may be interested in the CL Answer about Niagen:

Dr Wm Martin11047
July 6, 2016

Can you add detail to the "study which showed that a high-dose B complex supplement (with 1,000 mcg of B-12) hurt, rather than helped, people with diabetes and advanced kidney disease"? What kind of hurt, what kind of diabetes, and how was B-12 identified as the culprit?
July 8, 2016

Hi Dr. Martin - We've now added information in the answer above to address your questions. You can also find information about the study in the "Concerns and Cautions" section of the B Vitamins Review:

Dr Wm Martin11063
July 8, 2016

Just so I'm clear: The test subjects had both diabetes and advanced kidney disease? Thanks.
July 8, 2016

Yes, they had diabetes (either type 1 or type 2) as well as kidney disease (diabetic nephropathy).

Rose 9831
June 19, 2016

I take 1 mg. B12 (sublingual) 2 x a day. It has really helped with the ringing in my ears.

June 24, 2016

It's very irritating for you to post expressions like ". . .it has 3,000 mcg of B-12. . ."
Why not use "u" (lower case U) for micro and "m" for prefix meaning milli ?
The above is better expressed as ". . . 3 mG (milligram). . ." You do not help bring our nation up to speed in using normal metric prefixs. The US is only one of two or three countries in avoiding NORMAL international metric prefixes.
u = micro m = milli M = Mega
tera = T , giga = G , mega = M. , kilo, = k , milli = m , micro = u
mcg = very poor expression intended to mean micro.

June 24, 2016

Hi Gerhardt - We are aware that ug (or more correctly, μg - using the Greek letter Mu) represents micrograms. However, the alternate use of "mcg" is still recommended when communicating medical information in the U.S. and we believe that it is more understandable to our readers, most of whom are not scientists.

August 24, 2016

Good answer. Thank you!

October 3, 2016

"mg" and "mcg" is how most of our vitamins are labeled. I also take a prescription thyroid that is labeled as "MG". Not everyone who posts here is an M.D.

Susan 12804
March 8, 2017

Yeah, but we are used to using mcg for micrograms. Using "u" is confusing to most people; except, lab workers.

March 8, 2017

Yes! Some of us take more time to switch over to European ways!

Virginia 12850
March 23, 2017

I appreciated this contribution and am glad to also have read the commentary to it. Informative!

March 29, 2017

I strongly support Gerhardt's suggestion. To suggest it takes scientific knowledge to understand basic symbols which alternately simplify the contents at a glance is a bit insulting to the consumer intelligence. Additionally, when listed ingredients and nutritional amounts are shrunk down on labels to the point of requiring a magnifying glass to read without straining,
--- It further underscores the difficult hurdles most consumers encounter in an industry that is poorly monitored, overrun with production standards
and methods which threaten human health. Your recent article suggesting 62% of pill manufacturing facilities have non-compliant record histories (going from memory so correct me if wrong), points to some potential health risks to us, the consuming public .
--Given the announced budget cuts targeting FDA and EPA, existing deficient inspection protocols and schedules are going to increase adverse health effects.
It is a documented fact 17% of imported foods from Mexico are found to be contaminated . Although I'm getting off topic a bit, I just want to conclude the very reason I subscribed to ConsumerLabs is to obtain information that is not adequately
made available to the public, and many of us are sure to increase the level of concerns in this forum, given the exposure of so many harmful substances we experience daily .
April 6, 2017

Thank you for your kind words, Henry. You are correct about the percentage of dietary supplement manufacturing sites found by the FDA to have manufacturing violations in 2016:

December 4, 2018

I plan on initiating the use of vitamin B-12 mainly because I am 79 years old and recently experienced some memory and energy problems. I'm under a doctor's care and she has me on mementine (1 5MG TAB twice daily) and donepezil (1 10MG Tablet every evening). They have provided excellent results . However, I'm hoping for additional hely from the B 12. My problem is dosage. Recommended dosages are all over the place. Today I got an email from
Stop Aging Now recommending taking one 5000 mcg of MAX-B12 5000 daily.

Statements in your current review of B 12 do not recommend that high of a dosage. What is the correct dosage?
December 4, 2018

Hi Ronald - As we explain in another answer ( taking vitamin B12 will likely only help you if are not getting enough from your diet or have trouble extracting it from food, which is common among older people.

Unless you are severely deficient, there is no good reason to take a dose of 5,000 mcg, which is about 2,000 times the daily requirement, and, as we have noted, there are potential risks with getting too much B12.

For more appropriate dosing see the B12 (cobolamine) section of of our B-Vitamins Review at The Review includes our Top Pick for a B12 supplement.

June 12, 2016

I read a lot and there was/is a consistent thread to take the methylcobalamin form (not the cyanocobalamin form) sublingually. So, I take one 5,000 methylcobalamin sublingually about once a week.

My doctor says she is happy with my B-12 level.
June 13, 2016

Hi Bruce - Thank you for sharing your experience using this form of B-12. You can find more about the different forms of B-12, and sublingual B-12, here:

May 11, 2016

I took B-12 because of all the Hype, turns out I was normal and in a blood test, my B-12 was high and the doctor told me to quit taking it, it was dangerous to take too much!

May 3, 2016

Years ago (over 40 years ago), my family doctor did a house call when my ex-wife was really sick. He gave her and injection of B-12 and it really perked her up. He was ready to put her in the hospital but didn't need to after the injection.

I have taken oral B-12 for many years. I am unaware of any negative side effects. Have taken as much as 5,000 mcg per say but take about 300 mcg now.

Everyone's system is different.
May 3, 2016

Hi John - Thank you for sharing your experience. From your description it sounds like your ex-wife might have had a B-12 deficiency.

July 30, 2015

My doctor administered a B-12 injection for my daughter and she had severe adverse neurological reaction. It has been over 1 yr and she still has evidence of side effects. We have been told B12 toxicity is uncommon. Has anyone experienced such side effects?

Carol 8707
May 15, 2016

YES! My doctor gave me Vitamin B!2 last August -- I did have a severe neurological reaction that lasted for several hours whenI wanted to jump out of my skin, and while it calmed down a bit, I have not been the same since. I did my own research and discovered it could cause such a reaction in those who are histamine sensitive. I have been following a strict low histamine diet, and at least am somewhat functional, but lost 7 months of my life to anxiety, depression, and what I can only call heebie-jeebies. You must find a naturopath or other practitioner who understands this relatively newly isolated condition. Believe me, it has been hell.
May 17, 2016

Hi Carol - As noted in our Review (, although rare, there have been reports of possible allergic reaction to vitamin B12 supplementation.

June 20, 2016

Yes, I believe that is somewhat similar to my experience from taking the B12, 1,000 mcg daily. Too bad the dr. didn't understand.

June 20, 2016

Now I have a-fib because it stressed my heart so much and they don't get that either.

August 24, 2016

Please see my comment on High B12 levels and the MTHFR gene.

August 24, 2016

You are 100% right Carol. If you have the gene that doesn't function properly, MTHFR, you cannot metabolize B vitamins correctly. A LOT of people have this issue and don't know about it!
Google MTHFR there are a lot of informative websites about this condition.

August 30, 2016

You, and the woman above whose daughter had bad reactions to B-12, may have methylation issues that sometimes make one intolerant of methyl-B12. If you have an MTHFR snp (as I do) with other snps that ride along with it, you may do better with a combination of adeno-B12 and hydroxo-B12. It made an amazing difference for me. I use the ones from Seeking Health. Hope this helps.
August 30, 2016

Hi Dale - Thank you for sharing your experience with these forms of B-12. You may be interested in our CL Answer about MTHFR mutation and B vitamins:
September 22, 2016
May 15, 2019

Hi, Lynne11193.

Can you share with me some resources for reading about MTHFR as it relates to a B12 adverse reaction?

Thank you in advance!

July 15, 2015

My ex-husband told me he received vitamin B12 injections from his doctor, and afterwards suffered extreme itching. I recommended the sublingual B12 tablets instead of the injections. The large amount received at one time could cause itching.

December 12, 2014

I took B12 1,000mcg for six months. Didn't feel any different. Went off it and have been suffering from speeding heart and palpitations, problems I never had before the drug.

December 12, 2014

I'd just add a friendly reminder that correlation doesn't guarantee causation. I recognize that your heart symptoms could be connected to going off the supplement, but it could also be coincidence, meaning there is something else causing the new problems. I hope you'll get your symptoms checked by a doctor soon.

December 13, 2014

I have taken B12 supplements and also some shots now and then in the past without any discernable effect. It may be that enough of this vitamin is enough and I was getting enough in the diet.

January 14, 2015

The heart rhythm problem is definitely from taking too much B12. Going off the 1,000 mcg stressed my heart but the doctors who prescribe these things wash their hands of you when you come back to them with problems.

December 11, 2014


December 11, 2014

I think it is more complex... using serums, creams, that help cell rejuvenation and to firm and tighten and make skin look younger, they all make skin more sensitive to sun exposure. ( what is a huge cause of skin cancer)
It is crucial to be aware to always wear sun protection, when outside and reapply when needed.I have been using Vit C serums since years under my sun cream and believe it actually helps preventing sun rays to damage my skin. And I live in Hawaii.
Bottomline: using strong Vit serums, doing laser treatment, peels.... they all demand to stay out of the sun as much as possible.

December 13, 2014


December 10, 2014

When my 70 yr mother would have severe vertigo, a
B12 injection stopped the vertigo almost immediately.
It was years later we learned B12 deficiencies were common
for people being treated with antacids for ulcers.

December 10, 2014

there are certain drugs that rob your body of B12 (metformin and antacids) thereby creating a need for supplementation.

December 10, 2014

My father, in his late 80s, had to switch from oral high dose Vitamin B12 to biweekly B12 injections to manage pernicious anemia (loss of intrinsic factor). Without the B12 shots, he became very lethargic. I think older folks should check their B12 level and if deficient, try high dose oral B12. If that doesn't work, consider injections.

June 24, 2015

Sublingual tablets you suck have now been found to be as affective as injections -- in some studies I've read. The usual protocol is 2 weeks of sublingual daily initially, followed by a tablet about once a month or once a week. I believe the daily dose recommended was 1000mcg or 2000 mcg. It worked for me - my levels went up to 500 in a blood test (from 199 or 200) homocystine levels down. You can find these B12 studies on line, I don't have the reference in hand, also I am not an MD or PHD, just my personal experience.

September 20, 2016

IT COULD BE B12 ? An Epidemic of Misdiagnoses .writing by SALLY M. PACHOLOK,R.N.,B.S.N.&JEFFREY J. STUART, D.O. MAY BE THE ANSWER.

February 24, 2019

Kathleen, sublingual means "under the tongue". Thus, sublingual tablets should be dissolved under the tongue for absorbtion, since that area has more blood vessels that are close to the surface of the mucous membrane and can absorb more readily. If you just suck the tablets, you are likely just swallowing the B12 and it is less likely to be absorbed in the GI tract.
February 25, 2019

As explained in the B12 section of our B Vitamins Review, research suggests that the B12 from sublingual formulations is likely just being absorbed in the stomach, not really in the mouth, and appears to be no better than a tablet. See

December 10, 2014

Genetics play a huge role in how much one needs.

December 10, 2014

I have always felt it was better to take a B complex rather than individual B supplements. I take two tablespoons of nutritional yeast (all the B vitamins), and later in the day a B-50 capsule, and at 86 I am doing very well health wise.

June 24, 2015

I agree somewhat, altho I am only deficient in B12. I take my B12 with a multivitamin and followed by a full meal -- around lunch time when digestion is excellent (noon to 1pm or 2pm in daylight savings time).

April 24, 2016

If you take all B's in one pill how would you know which one is the problem?

December 10, 2014

It helps neuropathy and phathom pains. I take 3,000 every day and people on amputee site take 5,000....some take it two times a day. I tried to take that much and I broke out in hives.

May 8, 2016

I am concerned about absorption so I take a 5-MTHFR formula as a topical cream. A friend who has the genetic malfunction (MTHFR test) was told by her doctor to use this rather than Cerafolin. Sounded good to me so I have opted for this formula and a TransDHEA Cream. The 5-MTHFR formula comes out red but completely disappears when I rub it in.

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