Thyroid UK

B12 side effects

Hey guys

Sorry if just worrying but so many things have changed the past few days. Okay so I previously mentioned reacting to the Vit d sublingual oil and it making me feel a little shakey immediately after so I reduced the dose a little and I'm no longer reacting to this now so happy with that now.

However, the B12 and b complex have been working in a way I was not expecting and I'm also a little worried about the dose. I already mentioned that my eye problems I've had over the past two years seem to be completely reversing in a matter of days of taking it and even today, I could see miles down the street and all the blurriness has completely disappeared which is obviously great and dilation in pupils are improving every day.

But I'm worried about what happened today after taking them as I had soooooo much energy, I literally didn't know what to do with it and felt like my thoughts racing. I felt excitement for no real reason and a little too happy maybe lol. Anyone I spoke to on the phone, asked me what was going on as apparently I was talking so fast and sounded so ummm not my normal self - as in slow and considered. I was pacing a little too. I did then crash quite a bit maybe 3-4 hours later and became quite tired. I feel a little more balanced now although strangely very warm as normally I'm a cold person but I'm assuming this isn't quite normal or is it simply because I'm not used to having that kind of energy?? I know I've prob been deficient for a very long time?

It's just worrying me a little as not sure if this kind of reaction after just a week of taking it when low anyway is that normal? Do you think I should maybe get a lower dose?

28 Replies

One possible side effect of taking high dose B12 is low potassium.

I started taking a small dose of a potassium supplement with my B12 and they did help. I found that as I adapted to the B12 my need for extra potassium became less. I don't take extra potassium very often any more.

I am aware that the best way of increasing potassium is by eating foods high in it, but I'm simply not that organised. Supplements are a lazy way out that is perfect for me. I keep the dose low, and definitely don't exceed the dose suggested on the bottle.

Whether this has anything to do with your experience I couldn't say.

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Hiya, thank you, okay will look into that - gosh so many things to think about, i really know nothing about vitamins lol.

I think I'm going to give it a break tomorrow as even in the last hour, I have weird pains and uncomfortable sensations everywhere - back of head which seems to be spreading upward, overly warm skin patches, weird feelings in my veins and especially my arms, funny bone thing and fingers. I wont give up though as I'm assuming the massive improvements in my sight must mean I actually really need it. I will try and get some sleep and have a more sensible think about it tomorrow :-)

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I tend to eat a Bannana when I feel I am going to crash as the have a good amount of Potassium in the. Not keen on them but the do work also if you are feeling nauseous or bad headache


B12 is used in the methionine cycle. It needs cofactors to do its job, and enough methylfolate coming out if the folate cycle which feeds it. All of which can start mobilizing toxins.

So there's a lot going on.

Sounds like you became a little manic. You can have other psychiatric type symptoms, too, as you begin to supplement. Not a reason to run off and get some psychiatric drug, but having these symptoms means something isn't balanced properly.

Some thoughts, and you will have to experiment...

Eat a good amount of protein for adequate amino acids, which are needed cofactors. Try around 1.4g/kg a day. (If you're a vegan, may be time to reconsider, along with the B12 deficiency.

You can try separate amino acids, too. Taurine can calm manic symptoms. You may need methionine, glycine, or cysteine. But eating mirecprotein can help...

Next, you might try Thorne MethylGuard Plus, which has a balanced set of nutrients that support use of B12, like folate and riboflavin.

In addition to potassium, most people are magnesium deficient. Watch for arsenic contamination when choosing a magnesium glycinate supplement. Magnesium citrate or taurate can work, too. Not magnesium sulfate or oxide. About 4-800mg a day. (Diarrhea would be your clue that you're taking too much.)

B12 is a good thing. But sounds like you need more than just B12.

You might also educate yourself on methylation, which will help you understand the suggestions I made. Google methylation and Ben Lynch or Amy Yasko to get an overview.


Hi there, than you very much. I don't think it's the amount of protein as I've been obsessed with steak steak and more steak recently and lots of cheese lol. I did go off mackeral for some strange reason as have eaten this all my life. My iron is low though, I know I saw it mentioned as a caution with B12 but I am taking prescribed iron supplements although only taking half prescribed amount.

In regards to the thorne methylguardplus, I have been taking thorne basic b which has thiamin, riboflavin, niacin, vitb6, folate, biotin, pantothenic acid included. It also lists magnesium laurate and citrate in other ingredients but I will assume not in required doses. Is the methylguard one still likely to be better?

In regards to potassium, the last blood test showed okay levels 3.8, but I will get a supplement to try.

Magnesium is the one thing I do not have any clue as to levels in me but I have already ordered some but have not yet turned up.

Arsenic? Will this be listed as ingredient? I'm assuming not but will watch out.

Okay will have a google at your suggestions, just been struggling to keep new info in my head lol.

THanks again :-)


In regards to potassium, the last blood test showed okay levels 3.8, but I will get a supplement to try.

When you compare that to the reference range, was it low? It certainly sounds it. I always assume (on the basis of zero evidence) that mid-range is a sensible place for sodium and potassium to be.


Sorry, just double checked. It was 3.9 (3.5-5.3) so I suppose a little less mid range. sodium was 137 (133-146).


So with those ranges I would want potassium to be 4.4 and sodium to be 139 or 140.

If you've increased your consumption of potassium containing foods though, the result may be out-of-date.

I should stress again that I have absolutely no evidence for thinking mid-range is a good level to be.

I just know that one day, in hospital, my potassium matched the bottom of the range and I felt truly awful.


If you're craving steak, that's probably a clue that your body needs more amino acids for some reason. Could be you're not digesting well, could be you're toxic, could be a parasite like a tapeworm, could be an infection - I have one that causes me to suck up amino acids.

Make sure you get 3 healthy portions a day of varied protein sources... meat, fish, eggs, nuts, seeds, and possibly a pea or bovine gelatin protein powder.

MethylGuard Plus is stronger than the Thorne basic B. You can take both together, maybe 2 capsules if the MethylGuard Plus You could also Neurochondria plus Anti-oxidant together in their product line. It's more expensive, but beats going crazy ...

Most magnesium on the US market has arsenic contamination - I think it's found in the same rocks. It us definitely not listed as an ingredient, but it's there! Arsenic is the #1 worst toxin for humans - it's widespread and linked to many serious diseases.

I choose supplements from companies that are meticulous about testing ingredients. Brands I feel OK with are Thorne, Seeking Health, Designs for Health, and Doctors Best.

You might also pay attention to your gut health, which could be the root of all this.

A good primer in nutrients and the brain is Patrick Holford's New Optimum Nutrition for the Brain. He runs a clinic in London, and the book is excellent at explaining concepts, with good diagrams.

Best wishes as you experiment, and please reach out if you start to feel really off kilter.

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I do really feel off-kilter today :-(

I have a little one at school - so a tapeworm wouldn't be that shocking lol! I could take a tapeworm treatment anyway I suppose.

My digestive system used to be awful since I was kid but it has been working very well since i gave up gluten. no signs of problems - no gas, no foul smell, no constipation/looseness, all seemingly perfect deposits as per the poo scale lol etc. I was always very unwell and was always falling asleep before I gave up gluten and even have NHS diagnosis even though not coeliac because of the improvements of my autoimmunity and other conditions so may have been low on most things for quite some time etc.

Okay, I will increase proteins.

Thank you :-)


You are welcome.

You might also consider a Genova Diagnostics NutrEval test, which might help identify all your deficiencies. Sounds like you have multiple issues.

Take care....


Hello an sorry to bother you again, where do I go about getting one of those tests, i did google it but it seemed in the US and mentioned clinician log in? Thank you :-)


Magnesium glycinate is good and doesn't cause stomach upsets.


Hi, I just had a quick look at what foods contain potassium/magnesium and I've been eating an increased amount of these since my last blood test. I've always had a banana every day and often new potatoes. But recently I've been eating a whole lot more sweet potatoes, spinach and nuts although strangely have gone off tomatoes all of a sudden. What If I'm too high, am a little worried as apparently it's just as bad to go high on these two.

The only other new symptom I'm having is needing the loo more and being thirstier, does that indicate anything more specific.

I've got to say, everything aches this morning, muscles, back, stomach on one side, arms and shoulders greatly and everything. Feels like I did a whole lot of exercise yesterday, which I didn't lol.


I think you need to ask for help on the Pernicious Anaemia Society forum. They will know all about the side effects of taking B12.


Okay will do :-)


Have your calcium level checked for those symptoms.


My calcium was fine last time I checked, have never had a problem with this - at least since I gave up gluten. My last dexa scan showed my bones has healed to normal too after going GF.

I felt so exhausted, I went back to bed for the first time today and slept the whole time and only just woke up three hours later very sweaty and lines on my skin everywhere. I did dream for the first time in a couple of years lol ????


The vitamin D can interact with calcium.

Your symptoms sound like an electrolyte imbalance.


I've not had issues with calcium before and I haven't taken that much vit D yet as even skipped a few days of this so only had it a few days but I can stop this for a while if worth seeing if problem goes away and go back on it later.

Okay so maybe sugars and salts? Stupid question but Is it worth trying some of those Dioralyte sachets lol?


One day, I developed angina (I had to look it up), kidney pain, thirst, peeing constantly and severe keg cramping...

The answer was.... calcium deficiency. I'd never had it before either.

Shortage of electrolyte minerals can cause your heart to stop, too.

Worth checking out... potassium, sodium, magnesium, and calcium should all be in a harmonious balance.



Saggyuk Ohh the joys of dreams - I miss them too! Can't remember the last time I had one. Is that a hypo thing? Hope you feel better soon.


I don't think it is a hypo thing to be honest, I've never had a problem dreaming in all the twenty years I've had issues with my thyroid, just the past year or so. Well I wouldn't say it was a comfortable dream - rather strange lmao!!


May be try a slower pace to get your body used to things gradually. Also as you find your body wanting to be more energetic that don't use it up all at one! That's likely to make you crash! Lots of changes happening so be kind to yourself.


one over-energetic leap forward = two steps back, or injury :-)

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I didn't do more than usual, well apart from the pacing and over sped talking lol but will bear that in mind x


Hello again, I'd go with the advice above from Learner 1; Magnesium needs to be in balance with the amount of b vitamins you're on. High cocoa chocolate contains magnesium, so I eat it for medicinal reasons :-)

I take 1,000 mcg of B12 with no side effects, but 5,000 mcg made me a bit zingy when I started them, but I was deficient at the time. I think that b12 is finding itself going to nerves that need to be 'woken up' from sleep and at first it's a bit weird.

N-Acetyl-Cysteine sorted out chronic sinusitis due to it's mucus thinning properties, and is good for coughs too.. but it can interact with other meds so research it before you go for that one as it can cause issues with calcium in the kidneys as well (I take vitamin k2 to prevent calcium build up). NAC is one of several amino acids found in bone broths - which is one of the reasons why bone broth is great for colds. Making bone broth is a new hobby of mine! I also like L-theanine which is found in green tea.. but I usually just drink the tea rather than supplement.


THank you, hmm, I like the idea of that. Will be picking up some wonderful choc later, obviously for medincal purposes lol

THe Vit D I've been taken has K2 included. I might look into making bone broth but hate green tea lol. I do drink lots of normal tea but I assume that's not quite the same lol :-)

Yes, it might be worth me picking up some lower dose ones to be honest. I would have struggled if I had been at work today and I can't afford for that to happen.


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