Pernicious Anaemia Society
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How long do the injections last?

How long do the injections last?

Hi I'm Claire-louise

I had my injection in the beginning of March 2015.

I'm understood they would last 3 months .

I had 6 injections over 2 weeks .

But the last two weeks all the signs are coming back .

So tired

No energy

So much pain a crossed my chest and down my left arm


Can feel my heart like it's going to pop out

Plus so depressed.

I completely broke down on Tuesday .started crying at 1 PM Just couldn't stop saw my wonderful gp at 4pm

Had more blood test on Thursday receive results tomorrow Monday.

I just want to feel me again

Full of life.

Always busy not wanting to just stay home in my pj's.

This is not me.

Has anyone else been the same as me .

They didn't last long the injections.

Can you have one a month .

Sorry for going on but no one understands.

Say low b12 and it like ok so what ?

Thanks again for reading

2 Replies

People vary a lot in how long they maintain B12 but this isn't reflected adequately in either guidance or the text books.

I find that my B12 runs out within 24 hours of an injection but I don't think that is necessarily reflected in serum B12 results.

Someone recently posted the following article

which referenced a study in denmark where 30% of people receiving B12 supplementation had developed an immune reaction which meant that their B12 levels were high but the process that transferred B12 to cells doesn't work properly so they are functionally B12 deficient.

You certainly aren't alone but that doesn't mean that it is going to be easy to get through to your GP

1 like

Hi Claire-lou,

You definitely are not the only one who does not do well on the standard B12 jab once every 3 months.

To read many more see:

One size treatment just does not do the same for all, we all are deficient initially of B12, but the reasons why vary greatly and the treatment just does not work the same for all. We do not all fit in the on size 10, and people with PA/B12 def in France, Germany, Holland etc get the same B12 jab more frequently as a standard treatment. It is very strange that only an UK resident is expected to last 1or 2 months longer on the same B12 injections than those in other EU countries. Yes it keeps you alive, but it does not cater for quality of life, nor for differences in age, body weight or reasons to have become B12 def.

Also this link below shows how some can have a B12 functional def see:

Pract Neurol. 2009 Feb;9(1):37-41. doi: 10.1136/jnnp.2008.161968.

Functional vitamin B12 deficiency.


We describe a case of functional vitamin B12 deficiency where the repeated measurement of a serum B12 level within the normal range led to delay in the diagnosis of subacute combined degeneration of the spinal cord, and possibly permanent neurological damage as a result. Failure of intracellular transport of B12 by transcobalamin-2 can lead to functional B12 deficiency but with apparently normal serum levels, and is suggested by raised levels of either serum methylmalonic acid or homocysteine, associated with low levels of transcobalamin-2. Such patients may respond to repeated high-dose injections of B12.

Try your GP, try to see a haematologist, it can all help, and sometimes if not doing well on standard treatment means you have now become folate def and or iron def etc. Thyroid problems are also very common with PA/B12 def so should be tested etc.

But if all ells fails learning to self treat, what ever way, may be the only option left.

Many here do, or learn to self inject and get their B12 abroad (or online etc) or find other B12 products that work for them to keep them topped up and well.

I hope your appointment goes well on Monday and you will be helped to feel a lolt better again,

Kind regards,



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