Pernicious Anaemia Society
14,247 members10,202 posts

B12 injections - how soon before I notice a difference

I have just been diagnosed with B12 and vitamin D deficency. I have had my first injection and have another 5 over the next 3 weeks and started Fultium-D3 800iu tablets. How long might it be before I notice any difference. I have been goining downhill since the new year. I am so tired at the moment and struggle to more than sit in a chair or even be bothered to get a meal.

I would add I have ME and an underactive thyroid since 2007. The B12 deficency symptom list rings so many bells for me.

On looking on the internet this week it is amazing how much lack of B12, ME and underactive thyroid all have similar symptoms and I do wonder how long I have had B12 problems and whether this has been going on for a long time but my symptoms have all be attributed to ME.

I got the blood test just by chance when talking to my doctor about increasing the thyroxine dosage as I had hair loss generally ( no eyebrows now), dry skin, ridges in my nails as despite stopping work my ME had not improved, if fact I had less energy than a year before.

If it will help my test result was 110 for B12 and 45 nmol/L for Vitamin D.

Also are there any other blood tests I should be asking for to check if I am deficient in anything else?

4 Replies


Are you in the UK?

Some useful links for you. I have written some very detailed posts in past that may have some useful info if you search for them.



01656 769 717

If you leave a message they should get back to you within a few days.


Could it be B12?: An Epidemic of Misdiagnoses by Sally Pacholok and JJ. Stuart

What You Need to Know About Pernicious Anaemia and Vitamin B12 Deficiency by Martyn Hooper

UK Documents/Articles

BCSH Cobalamin and Folate Guidelines

Other links

Martyn Hooper is the chair of the PAS. there is a post on his blog which mentions the misdiagnosis of PA as ME/CFS.


Thanks sleepybunny for all the links.

This is all very new to me, less than 3 days since my diagnosis. I will slowly work my way through them. I see that the first one I read told me to get folate and ferratin levels checked as well. That's one question aleady for my GP.

Hopefully one of them will answer my question of how long I have to wait to notice any improvement.

1 like

Forgot to add I am in the UK



My understanding is that people's reactions are very individual when it comes to B12. Some people experience improvement within a few days. It took me several months before I noticed any substantial improvement. Some people do well on the standard NHS treatment, some people find they need to take extra. I know of some people who need to inject every day.

There are different forms of B12 (Cobalamin) eg cyanocobalamin, methylcobalamin, hydoxycobalamin and adenosylcobalamin. Some people respond better to a particular form of B12.

"Also are there any other blood tests I should be asking for to check"

You mention you have an underactive thyroid, there are quite a few on here who have both thyroid and B12 problems. Sadly sometimes auto-imune diseases come in clusters.

Coeliac Disease

Have you ever been checked for Coeliac disease? Again there are quite a few on here who have some degree of gluten intolerance and I think some with Coeliac disease.


You may find it interesting to look up MTHFR gene mutations.


Some medicines and drugs affect B12 and/or folate metabolism. See link below.

Nitrous Oxide

Have you had any surgery involving nitrous oxide? Nitrous Oxide can inactivate the B12 in your body.

" I do wonder how long I have had B12 problems and whether this has been going on for a long time but my symptoms have all be attributed to ME."

Although I believe that ME/CFS exists, my personal view is that some people who receive this label are actually suffering from some other condition that produces similar symptoms.

Have you ever been bitten by a tick? Lyme disease symptoms can overlap with those of ME/CFS, thyroid problems, B12 deficiency etc.


You may also like...