How long for a B12 injection to kick in?

[scadman]

I have been on B12 injections for approx. 18 months, initially at 12 week intervals, 2 months ago I persuaded my GP to reduce this to 10 weeks, but find all symptoms return at about 7-8 weeks later. I had an injection yesterday at 1.30 pm, went home and promptly fell asleep exhausted. Woke up this morning feeling 200% better, is the usual time span for an injection to kick in. I have a GP appointment next week to get blood tests and nerve conduction tests results, and want to suggest reducing down to 8 weeks between injections. I get the feeling sometimes she thinks I am not confident in how I describe the symptoms. I don't want to come across as too aggressive and assertive, but confident that what I am saying about feeling before and after an injection is accurate to what is normal. Thanks in advance for any info

[Gambit62 Administrator]

if you have neurological symptoms then the standard recommended in the BSCH guidelines, and the NICE guidelines is maintenance every 8 weeks

Your GP can access the guidelines through the BNF but you can access them here

onlinelibrary.wiley.com/doi...

some people do find that they feel wiped out after a B12 shot.

[scadman in reply to Gambit62]

Already been down that route with another GP, who emphasised the word "guidelines" does not mean mandatory treatment. This GP is more flexible and prepared to listen, hopefully the blood tests and nerve tests will convince her to reduce the time between injections. This may seem a silly question, but I've seen various posts that suggest taking B12 sublinguals between injections, what exactly is that and where do you get then from.

[Gambit62 Administrator in reply to scadman]

sublinguals are basically high dose tablets that disolve in the mouth. The theory is that this means that you absorb B12 through the membranes in the mouth though the practice seems to be that the amount absorbed is generally only just slightly better than that for the same dose just taken as a tablet - at just over 1% of the dose*. so from a 1000mcg sublingual you would get something around 10mcg. RDA for B12 varies from country to country but is 2.5mcg at the high end so that means that you would be taking in 4xRDA - so a little bit more than you would using if you are an average person.

High dose oral can be a very effective of keeping your levels high between maintenance doses but it doesn't work for everyone - for some people they can even be an effective form of treatment and not require maintenance shots but a) it isn't a licensed treatment in the UK and b) it doesn't work for everyone. The tablets are vitamin supplements so not covered by need for a prescription and, because B12 isn't toxic, there is no risk of overdosing if you take more. They also give you the opportunity to try different types of B12 to see what one works for you as you can get cyano, hydroxo, methyl and adenosyl sublinguals.

nasal sprays are another possibility - but even then the average absorption is 3% of the dose provided.

*This is the average for passive absorption of B12 - ie absorption outside the ileum and in the gut in general, so the 1% only applies to people who have impaired absorption through the ileum - people without absorption problems will absorb a lot more of the dose.

[Suzibelle]

My time span for feeling better after an injection is anything from overnight (as you mention) to several days. Still haven't figured out why the difference but I haven't been good at noting what else is going on in my life at the time to see if that's part of the problem. I've reduced the time between injections from once every 12 weeks to once every 7 weeks and am still assess that, too. Just explain it fairly simply to the GP or keep track of your symptoms in a diary for a while to show her what you mean. Good luck!