Thyroid UK
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Is it ok to take B12 with levothyroxine? Vitamin advice needed please!

Following up my post about bitter taste in mouth, sore tongue etc..... Research on the web has made me wonder if I have a vitamin b12 deficiency?

Can it do any harm to take a vitamin? And can I take it with Levo - I will obviously wait 4 hours so it doesn't interfere with absorption!

I'm desperate to try anything that will relieve the awful taste in my mouth but don't know a lot about vitamins etc....

And if I do, how soon would the b12 'kick in'?

Any help, very much appreciated!

6 Replies

All other medication and vitamins you are taking should be kept four hours apart from your levo to be on the safe side.

Moggie x


Thanks Moggie - will do!


It most certainly can do harm to take a vitamin.

B12 is usually regarded as one of the safest of all vitamins. It is difficult to find anything bad about it even in massive doses so long as you do not suffer from Leber's hereditary optic neuropathy.

By far the majority of B12 taken either never gets absorbed or can easily be excreted.

However, your problem is what to do if the B12 does help! By taking a B12 supplement you will make any standard B12 test result reflect your supplement rather than your effective level. Even with the newer Active B12 test it is advised to wait four weeks (I think) between any B12 supplement and the test.

You could end up having to supplement indefinitely without getting diagnosed properly. Not ideal. Especially if you actual need injections rather than simple tablet forms.

If possible get tested by GP now. If possible get privately tested using the Active B12 test (e.g. from Blue Horizon - see main Thyroid UK website). Then consider your options. At the same time, do NOT ignore the possibility.



Thanks Rod! You scared me a bit with your first comment but thank you very much for the info about B12.

It's a very good point that you make but where do I go for a private test please? It's not a world I'm familiar with. Will it cost a lot?

Thank you :)


The main Thyroid UK web site:

Do double-check that the company does the Active B12 test before you order a test.

Vitamin A and vitamin E can most certainly be harmful if too much is taken.



You could just start by asking your doctor to do the standard serum B12 test on the NHS. It's not a great test but if your levels are very low it will pick that up. Unfortunately a normal result does not exclude deficiency. If it comes back normal then think about the active B12 test, which you would have to pay for as Rod says.

Also don't forget to ask the doctor to test folate and iron/ferritin. Deficiencies in any of these things can cause a sore tongue.



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