How long does it take for B12 injecti... - Pernicious Anaemi...

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How long does it take for B12 injections to work

MKitty profile image

Hello all, I finished a course of 6 injections 4 weeks ago and do not feel any better. The nurse at our practice said they would take about 3 to 4 weeks to work. am I just being impatient. So so tired aching all over feel like I have permanent flu. pins and needles in right arm, toes and left side of my face have not improved. I also went gluten free of my own back to try and calm the bloating and the other nasties. but no change so gone back to the normal diet. Should I be taking supplements to help. Should I try to find some B12 tablets. I am on 100mg Levo and still not lost any weight. Should I send for another private blood test. Thank you in advance for any advice.

35 Replies


I'm no expert, having only recently found myself in a similar position (in fact I'm not due to start my loading dosage until next week). But I've done a lot of reading in a short time so I'll answer what I can in an effort to give back some of the help I've already received.

Was your dosage following a low test? If so the numbers would help others with more expertise.

From my reading of the expert literature, the position SHOULD be to treat the symptoms, not to just hand out a 'standard' 6 injections. However, that seems to be the norm in many practices (including mine) even though the NICE standards suggest when there are neurological symptoms (such as pins and needles) the treatment should be alternate days UNTIL there is no further improvement.

People seem to react differently to the injections, with some immediate improvement and some much slower.

Have they suggested a follow up blood test, or put you on the standard 3 month maintenance dose? (With neuro symptoms it should be 2, but again that seems to be unknown in many areas).

If the cause of the B12 deficiency is malabsorption (PA or similar issues) then tablets are often not useful unless they are extra high doses, as the body may not absorb more than 1%.

Fortunately, it seems that the body disposes of extra B12 itself, so overdosing seems to be almost impossible. The only issue may be that it might elevate blood levels in any test and give a GP a reason to think you miraculously 'cured' (In most cases, the guidelines are clear that the injections should be for life because there is no cure)

I'm investigating sprays and other methods, though some people seem to find that self injecting is the only solution that works for them.

I'm sure more experienced members will add more, but hope that was some help.


Gambit62 profile image
Gambit62Administrator in reply to GavinUK

GavinUK - some B12 is absorbed outside the ileum - on average this amounts to about 1% of B12 absorbed so if you have an absorption problem then likelihood is that the amounts absorbed will be around 1% not 10% ....

GavinUK profile image
GavinUK in reply to Gambit62

Thanks for the correction - I'll edit it. This is why I'm happy there are experts here :)

closere353 profile image
closere353 in reply to GavinUK

Vitamin B12 - This tablet took my Vitamin B12 levels from dangerously low to so high I can only take them every other day.

No answer just wanted to say I feel same as you, I actually feel worse since my loading doses two weeks ago, really hope you get some good advice and feel better soon xx

MKitty profile image
MKitty in reply to Leigh33

Hi Leigh33 sorry you feel bad.Its horrible. I guess I maybe thought the injections would make everything go away. but for me nothing has changed. I do hope it's better for you. I have so many different things wrong and im sure the family think I'm a hypochondriac. take care

Mummy365 profile image
Mummy365 in reply to Leigh33

Hey I'm a newbie I'd my first load up dosage last thur, then ystdy back again on Thurs. I feel like a pair of old pants that don't want to get up and dance. Chores take forever which is hard when house proud, autistic son, mental health issues myself and fibromyalgia every day is a constant battle body and mind and find myself having to go back to bed for a few hours. I could sleep 24/7 don't think it would make a difference tbh. Ystdy injection now it gave me pins and needles also, is anyone that is on the injections also on folic acid as apparently I shouldn't have been took of meds for either. When they diagnose you with this are you not regularly checked where your markers are at? Does it ever get any easier? As with my other health issues I find it hard to differentiate between the two

Sorry for rant, I'm just so confused what's happening to my body. Tia

Leigh33 profile image
Leigh33 in reply to Mummy365

Hi, I found that my symptoms became a lot more exaggerated when I had my loading injections, and I still find for a week or two after my 3 monthly injections symptoms appear worse, but once the b12 gets to where it needs to be you will find you have some relief from the symptoms.....until ur next injection is due.....(this is just my experience) but you can supplement with oral or nasal sprays, and patches (not sure how good these are I haven't used them) and I find they help until my next injection. Hope ur feeling better soon x

MKitty profile image
MKitty in reply to Leigh33

thank you

Mummy365 profile image
Mummy365 in reply to Leigh33

Thank you for a reply, everything I do leaves me sore tired breathless. I was always on the go never stopped. Now lucky I can get started at times. I am sick being sick, I'm like a flat pack and extras left over. As I said been ill with other stuff from 1995 and my poor son doesn't understand why mummy sick or tired. He'll never understand. Hate what memories he's building off me. I try my best, but I tire so easily. I went nuts cleaning, washing hung out moping etc. Was still awake gone 4:30am cause I fell asleep and I detest I didn't see or put my son to bed. I want and need better for him.

My right arm takes the worst hit, like getting it there thur wee nurse just asked how I was and the tears started. I suffer nausea 24/7 but after loader I can't eat it wipes me, my appetite and makes me feel sick unsure if that's just me. A friend said she could see I'd lost weight in my face. I call it vaping cheeks lol

Thanks for letting me rant, I wasn't told what my markers were, what they should be or told anything about this, I've been trying to find out myself plus a friend has it and 2 wks sometimes 3 before her 3mt jab she goes downhill again and she's on it years x

Brookieg profile image
Brookieg in reply to Mummy365

My heart goes out to you. I've had no energy since having both my boys and I get the whole 'mummy is sick again', it breaks my heart. Hang in there, it took along while for you to get like this it's going to take a little bit of work to get back to being you again xo

mirelle25 profile image
mirelle25 in reply to Mummy365

I started loading dose last Monday and I feel 10 times worse my whole body aches I can’t even hang up a washing and I’m out of breath and I lost my sense of smell about 7 month ago due to this deficiency, I’m now starting to smell things now and then but my body feels like a tonne weight most of the time, my nurse said I won’t feel any improvement till after my booster shot which will be in 3 months time 😢 surely there is more they can do for this I feel so tired and deflated all the time

I have been on injections since early May - they just can't figure out what I need (but neither can I). I have maybe 1-2 decent days a week, which is better than before. I am trying to be patient but I want to feel better also. I feel like a hypochondriac sometimes, but I know I am not making it up.

MKitty profile image
MKitty in reply to Lorilee60

lorilee60 so you have been given more than 6 loading doses on the nhs

I had an injection to start and then 3 weeks later, 2 per week for 3 weeks, then one a week for 3 weeks. Now they ordered 2 a week for 3 weeks again.

Have you had a vitamin D test? Only asking as some symptoms do overlap, especially as you have Thyroid problems- you are more susceptible to low vit D. It made me feel terrible, achy and very tired when I was low. Also vit B12 & D, folate and iron ALL have to at an optimal level to feel the best.

MKitty profile image
MKitty in reply to greenbexy

Hello greenbexy thank you for your reply. no my Vit D hasn't been tested, but have been taking a supplement for over a year because I live in Scotland and we don't see much sun. So am I wrong to assume that the daily dose might not be enough.

greenbexy profile image
greenbexy in reply to MKitty

It might not be enough, best to get a recent test before upping the dose. I keep having loading doses of around 20000 units over several weeks, but I still can't manage and optimal level for a length of time. So I'm back to the GP for a maintenance dose. We don't get much sun in Lancashire either!

MKitty profile image
MKitty in reply to greenbexy

thank you I will send for another kit from BH no way will the GP test Vit D.

maybe we should all emigrate to where the sun shines all day everyday. Boy that would be nice.

Gambit62 profile image

MKitty - there isn't a simple answer to your question about how long it takes the injections to work. b12 is used by a lot of processes in the body and its sympotms may be caused by the lack of B12 for one or several processes. Some processes recover quickly - others will take much longer. If you had macrocytic anaemia this will take several months to clear because new health red blood cells will only be made as the old red blood cells 'die' and the average lifetime of a red blood cell is 4 months.

It is also quite common to feel a bit worse before you start to feel better - aches and pains can be worse and the flu type symptoms may actually be your immune system kicking back in and possibly going into overdrive fighting lots of low grade stuff that it hasn't been able to tackle properly - many of the symptoms we associate with being ill are actually ways in which the body fights infection - which includes raising temperature a little, rash type reactions. The aches and pains getting worse are possibly down to the role B12 plays in regulating neurotransmitters - the chemicals that carry signals between nerves - the signals will be getting through stronger and sometimes it takes the brain a while to adjust - the simile I use is comparison to an analogue radio when the signal is weak - you turn it up so you can hear the it above the white noise and then suddenly the signal comes through clearer and it is deafening.

Other processes can take a lot longer to heal - eg damage to the myelin lining around nerve cells.

If you are based in the UK there is a different protocol for treating neurological symptoms that is more aggressive - loading shots (3xweekly) should be continued until there is no further improvement in symptoms (with a review at 3 weeks) and then on to maintenance shots every 2 months.

If your folate levels were low when you started treatment there is also the possibility that you may have become folate deficient - as starting all the healing will take folate as well as B12.

Like so many have said on this forum, be patient, it took 4-6 month for my neurological symptoms to improve, my migraines improved within 2 month, thank goodness.

Also it's not a miracle cure, you have to expect an odd off day when things are out of balance inside your body, it's not just a vitaminB12 deficiency issue. Take the time to read lots of the posts on this site and on de PAS site, get informed and you will find answers to your what and why's and how. 😮😐

MKitty profile image
MKitty in reply to ACritical

I wish it were just an odd day.

Thank you for your reply.

kjl3 profile image
kjl3 in reply to ACritical

Did you have brain fog, trouble remembering, etc.?

ACritical profile image
ACritical in reply to kjl3

I felt very tired, couldn’t remember for instance what I just read when I tried reading books or online articles. I could no longer be relied upon, I was also very unsure walking, used a walking stick on bad days. I felt like things were in slow motion when I turned my head. I had a few falls, neurologist found out that I had no feeling in my legs below the knees and in my feet, she pushed a sharp implement in the skin and I felt absolutely nothing. I thought it had all to do with my migraine, it wasn’t. Migraines went first, fairly quick, still get them sporadically but less severe in pain and duration. No more chucking up for 3 days in a row. I am off all heavy medication and I have my life back, I am able to read again and retain what I read, walk every day 3-5 km, minimum 30 minutes. I do small weights and use my treadmill when the weather is too bad to go out.

I can relapse when I wait too long for my injection, migraines reappear and my legs don’t want to hold me up , I struggle with walking. Tiredness overwhelms me again.

If I can’t get my injection , I need them once a month ( as prescribed by my neurologist ) I try to get them privately or I do it myself subcutaneously. It takes longer to work but it does the trick within a day or 2. My GP only allows me to have 1 injection every 3 months now, no reason given.

I manage myself fairly well, a good diet is essential as keeping an eye on all the other vitamins and minerals my body need. I pay privately for blood tests. I supplement when necessary. Vitamin B12 deficiency runs in my family, didn’t know until I start researching, I realised my grandma as well as my mum suffered in silence. My daughter has been diagnosed and started her loading injections, again through suffering terrible migraines. Her headaches are much improved. However, healing, it does take time from a few month to 2 years depending the issues, to feel like you want to. My ear ringing has not improved, some days worse then others, I have learned to ignore the sound. Hope this answers your question.

kjl3 profile image
kjl3 in reply to ACritical

Wow, I’m glad you are doing better. I just started my injections 2 weeks ago (i have only had 2 so far) and i see very little improvement. I still feel foggy and not motivated. I’m hoping it will get better as time goes on and as i continue the injections.

ACritical profile image
ACritical in reply to kjl3

Keep the loading injections going until you see, feel improvement, you might need more then the usual 6, mine took longer, improvement gradually happened. I still can’t believe that a simple deficiency can cause so much havoc in the body and that a ordinary vitamin injection can help to bring the balance back so you can function normally. Remember it’s not just a vitamin B12 injection that will do this, it’s you listening to your body and realise what you put into it matters, i.e.what you eat and drink and how you treat your body. Diet and exercise com into this. Also when you catch a virus, expect a set back, don’t blame it on the B12 deficiency alone, give your body rest and what it needs.

I do want to add, I am not medically trained, I had a neurologist who treated the whole person not just the symptom, in my case the referral was initially for migraines, they got worse because of all the meds I took.

kjl3 profile image
kjl3 in reply to ACritical

Thanks! I am in the US and the neurologist ordered me to do injections once a week for 4 weeks and then monthly after that. There was never a ‘loading dose’ per say. However, she checked my intrinsic factor and that was fine ao i am able to obtain b12 orally. I am doing the b12 supplement along with the shot. I’m thinking maybe I need more? Did you take any other supplements while receiving the injections?

ACritical profile image
ACritical in reply to kjl3

Yes I did, I was also low in other vitamins like vitamin B9 /Folate and vitamin D. I do supplement and take vitamins D3 together with vitamin K2 they work together. For my migraine I also take the other vitamin B’s and magnesium in liquid form, only when needed. I try to get them through eating healthy food but as I have an absorbing problem, this doesn’t always work.

kjl3 profile image
kjl3 in reply to ACritical

I see, I think I am going to try the folate/folic acid and see if that helps at all.

Im not medically trained so these are just my thoughts on nutrients to consider as nothing seem to be the magic cure all for any of us.

I decided it is possible that if my body isnt absorbing b12, it may not be properly absorbing other nutrients either. Additionally when prescribed thyroid medication it does not change how you feel overnight so if you suppliment any of these i doubt an overnight correction will happen with them either.

Best of luck to you. I hope you begin to feel better soon

I'm the same just finished my loading injections and feeling crap . What do we do next ?


Not sure if this is still active but will love some advice!

I have recently been diagnosed with low iron, low folic acid and low b12 amongst other things. I have been taking iron tablets and folic acid tablets along with 6 injections over a 2 week period and have had a follow up blood test which shows that my iron and folic levels are good but my b12 levels are still abnormal. I am a confused, shouldn't the injections have helped improve my b12? I didn't feel better while having the injections or after so i'm not sure if its working! I have started to take b12 supplements. Has anyone else experienced this? What was your outcome? What an be a possible reason why it hasn't made a difference? I am disappointing as I have been taking extra care with my health and it doesn't seem like its helping :(

kjl3 profile image
kjl3 in reply to RWUK

I have recently been having issues with my b12 also. I’m no doctor but just a few suggestions. You should have your doctor check your intrinsic factor (to see if your body is able to properly absorb the b12 that you are taking in) also have them check your ANA to see if there are any autoimmune issues that are causing you to not be able to respond to b12 injections.

Ken-ard20 profile image
Ken-ard20 in reply to kjl3

I wish you right with intrinsic test my doc refused even after having bowel surgery.

But I had some tests done privately and test showed I needed vit d and other b vita although folic was not low but b12 was.It reflection on NHS at the moment

Hi there, just wondered where you did your private tests and how much they cost?

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