Log in
Pernicious Anaemia Society
17,124 members11,852 posts

SI B12 - needle size?


I’ve recently started to SI B12. Following the advice/recommendations given on the Forum, I’m using a BD Microlance 23G x1” blue needle. Is 1” sufficient for intramuscular? I inject into the thigh and I’m a slim female. Thanks

The ability to reply to this post has been turned off.
34 Replies

Yes, they should be fine (same as I use). The important thing is to make sure that you inject at 90 degrees so that you go directly down into the muscle.


Yes I do that. Thanks Foggyme.

1 like

If I were you I would get a finer needle i.e. with a higher gauge number . You can get a1 inch 25 gauge needle from Medisave , a 1 1/2 inch 27 gauge needle from Excange supplies . I found a1 inch 30 gauge needle at Bulk Syringes .com (in USA ) but they worked out very expensive with shipping . . Nevertheless , the 30 gauge needle is amazing —cannot feel a thing at all! Will only inject slowly though because of the fineness of the needle -but it suits me like no other .

1 like


1 like

Thanks Wedgewood, I'll look into it.

1 like

Hi Wedgewood and pas250218. Just a word of caution about the use of fine gauge needles (25G and above) for IM injections.

These very fine gauge needles are not manufactured or designed for IM injections. Rather, they are used for intradermal, interocular, dental and subcutaneous injections etc. In other words, for any type of injection that goes into less dense or fibrous tissue.

Because the needles are finer there is a greater risk of bending or snapping when used for deep IM injections - also a potential issue if the muscle goes into spasm during the injection (rare, but it does happen). And because the needles are so fine, there's also the risk of blow-back during the injection (blow-back is when too much pressure on the syringe plunger causes a pressure build up because the fluid cannot get into the muscle quickly enough, the needle and syring blow apart, wasting B12 and making it impossible to determine how much of the dose has actually been injected.

Here's a link to more information about needle selection:


And here’s a link to further information (chart on page eight that details different needle size/gauge and uses etc. And good for needle / syringe types - haven’t read the bits on injection technique so can't comment on that)


I know that these needle gauges suit you Wedgewood and am also aware of one other person who uses them ( Cetus) And yes, finer gauge needles can be less painful - but there are more risks associated with their use for IM injections and it's not something that manufacturers or healthcare professional recommend.

I certainly wouldn't recommend them for anyone new to self-injections - in fact, sorry to say, I wouldn't recommend needles with this thin gauge for IM injections at all. It introduces extra levels of unnecessary risk.

Not trying to rain on your injection parade wedgewood...Know you've been doing this for a while and are a practised hand...and this obviously suits you.

Just wasn't sure if you were aware of the additional risks and also want to make others aware of the potential problems associated with using needles outside the bounds of manufacturers (and medical) recommendations / advice 😉.


1 like

Yes you are right to point out the dangers involved Foggyme . I’m always very aware of them when I inject . But the difference with using the 30 gauge is enormous . Yes they are sold for use in dentistry . I think it’s best if I don’t recommend their use . I wish I hadn’t now . Thanks for pointing this out .


Hi Foggyme and wedgewood !

Thank you for your information on the smaller needles. I was aware of the problems of smaller needles but didn't think about warning people and feel I should have done.

I for one find the smaller needles (I now use 26G x 1") sooo much better that I would rather be aware of the risks and take extra care.

Some of it depends on how often you are injecting - if it's frequently then you get plenty of practice and the reduced bruising and tissue scaring is well worth it.

Please, Foggyme, would you consider the option of making people aware of the possilities AND potential risks of using finer needles? I agree it shouldn't be done without the caveat but it has made such a difference to my mornings (and probably my legs long term) that I would like to give others the chance to decide for themselves.

I believe Ashmead's Kernel posted some time ago about problems with tissue scarring over a long time and I am keen to avoid that if my aim of injections is to keep me alive for lots more years to come!! 😁 x

1 like

Hi deniseinmilden. Understand perfectly what you're saying. As I said in my reply to Wedgewood, I’m a great believer in in freedom of information....and speech..and...well...most things really. Enough information to make informed decisions etc....

I know that some people do use finer needles and that’s their choice (as it should be) but this is a tricky subject.

As an Admin, I cannot advise using dental / subcutaneous needles for IM injections - something that is contra to manufacturers / medical advice (and yes, medical advice is a problem for many here, but we're talking medical equipment that has been tested and assured for certain uses only😉).

Another potential problem is that we cannot make judgements in the forum about who could perhaps manage this safely...and who couldn’t.

If members of the forum wish to discuss this, then that’s their prerogative. But I'd suggest ALWAYS putting in the caveats and warnings...and if these are absent, then an Admin (if they spot the post) will probably pop up and advise against it (as we should).

Interestingly, the PAS are currently pulling together a research project to examine the differences in efficacy between SC and IM injection of B12 (never been properly researched before). It's hoped that if research evidence supports the notion that SC is as effective as IM injections for the delivery of B12, then this will eventually lead to a position whereby GPs are able to prescribe SC B12 for self-injection (as per with diabetics). And what a happy day that would be.

So yes...I really do get what you're saying...but there are some lines that Admin's (speaking for myself here) cannot cross.

And as with wedgewood, pleased that this has made a difference to your mornings...and your legs 😉😀.

1 like

Definitely - I'm very uncomfortable with advising on anything - other than being careful!

Really appreciate your care and guidance - thank you! x

1 like

Thanks deniseinmilden. Oh so much to be careful of...and wouldn't it be marvellous if we could reply on our medics to take that care on our behalf 🤔 😀.

I would dearly love to have a B12 universe where fora like this were obsolete...or where they were places where we could just pop in for a catch-up and chat with our pals.

Oh what happy days they would be 😀.

Hope you're managing in the heat - like you, I struggle - bit of a nightmare. But having grand children who hose me down in the garden helps 😂😂.


1 like


1 like

This sub thread is so very appropriate to me right now. I have just used my second 1” x 25g needle for IM in thigh. My daughter, who had been self injection for the past 10 years had a bad experience with a surgery supplied 1.5” x 23g needle and said she had been using 1” x 25g (orange) needles from the surgery until quite recently and found the thinner ones less painful. So I ordered a 100 each for both of us.

I did ask the surgery if they had any and the response I got was that 1” wasn’t deep enough - that was one of the nurses.

My daughter is on holiday at the moment so I will let her know of your concerns when she is back.

I have to say though, without presuming to make any recommendation 😊, the 25g needle slid in beautifully and with gentle pressure injected painlessly.

1 like

Hi Kebrecks. About needle length...

Your daughters' nurse is either taking a 'one-size-fits-all' approach to needle size...or she's based her opinion on knowing your daughters' size and weight.

The length of the needle used depends of the size of the individual and the depth of the subcutaneous layer of tissue that has to be injected through to reach the muscle, which sits underneath.

So...a 1” needle is appropriate for some one of small to average build (like me, and pas250218), a 1.5” needle would be needed for someone with a medium to large build, and an obese person would need an even longer needle - up to 3”. A person who is very thin and has little subcutaneous tissue would have to use a needle shorter than 1”.

So, needle size is relative, the main criteria being that it must be long enough to reach right down to the muscle - and that obviously depends on what size a person is 😉. And what area of the body is being injected.

As to the gauge (thickness of the needle)...23G is the usual recommended size for IM injections but up to 25G should not be a problem (okay for B12 which is 'thin' liquid, but might be a problem for something 'thicker' and injection needs to be done slowly).

Dental / subcutaneous needles (the sort under discussion here) are not suitable for IM injections.

Hope this helps and good luck with the injections...


I would agree with your assessment of needle length, Foggyme, but for the simple fact that the comment from the practice nurse, to which I was referring, was unambiguous. She said, categorically, a 1.5" needle is required. No if's No but's. The surgery also supply 1.5" x 23g needles but of the Safety design and neither of us get on with those.

1 like

Well...if it was a categorical statement, then she's taking a 'one-size-fits-all' approach...unless you're both slightly larger ladies, which only you can know 😉.

All the guidelines for needles length are as stated above - no categorical statements in them.

Go with what's suitable, within those guidelines, for your size and weight...which is what you appear to be doing.

As to needle design...I find that the simple basic design is what suits me best (perhaps because it’s what I'm used to), though there are those who do prefer the 'safety' design.

I've given hundreds (if not thousands) of injections and never adhered to the one size for all principle. Always selected needle size based on patients size and weight.

On good note - it's very rare to find a surgery that will provide equipment for self-injecting B12 - now if they could just up their game and hand out appropriately tailored advice about needle size...


Oh dear Foggyme thanks for the giggle. Firstly my daughter is about 5’4” and almost as fit as the proverbial butchers bitch so the 1” variety is just fine I would expect. But as for me I am her father and although not anywhere near sylphlike do have muscular thighs with minimal fat covering.

Our surgery have always handed over the syringes and needles to self injectors so I thought it was normal practice. They just don’t like going outside the NICE guidelines for frequency of injection.

1 like

And I'm joining you in that giggle...just imagining two lean mean women...a match for any one-size-fits-all-nurse, if the ever was one (or should I say two 😉).

As for the NICE guidelines...the PAS have been lobbying to have these changed for some time and NICE has recently agreed to review the current guidelines...and requested input from the PAS. It won't be quick, but fingers crossed 🤞

Hi Wedgewood. Oh please don't worry about this.

I’m a great believer in in freedom of information....and speech..and...well...most things really. Enough information to make informed decisions etc....

I can understand why you recommended these - they helped you and we all want to help others.

Recommend again? To be honest, as a general rule, I wouldn’t 😉. If only to keep your own self safe (public forum / potential liability etc.).

But really pleased that this works for you 😉😀.


You were absolutely right to point out the hazards of using very fine needles i.e. 30 gauge . I will use 27 gauge in future . It’s great to have you watching out for us Foggyme ! We need you !

1 like

Ah bless you Wedgewood. As an Admin it's always quite difficult saying things people might not want to hear...and I'm always conscious of not wanting to upset anyone 🤐😉.

So thank you for that 👍

1 like

"needles are finer there is a greater risk of bending or snapping when used for deep IM injections"??

That couldn't be further from the reality. I've been using 30g x 1" for about 5 yrs now.

If you tighten the muscle just before ... the needle might bend a little - if hold the muscle loose (as you are supposed to), it never bends for me. At first, when I unknowingly clenched my muscle and bent the needle, I would try to bend it to break it in order to see the failure rate when bent - no matter how vigorous I bent the needle back and forth I could not get it to 'snap' (I use a BD 30g).

PAS250218 - try bending and breaking a BD 30g needle yourself for a reality check.

I'm assuming that 'reality' is based on your experience.

Reality - 30G needles can and do snap.

Reality check - You might not have seen it, but I have. I've also seen snapped needles that have had to be surgically removed.

Using what are essentially dental / subcutaneous needles for IM injections is not something that we will be recommending...in line with manufacturers and medical guidelines.

Forum members are free to make their own informed decisions about what equipment they choose to use to self-inject.

It's quite a shame that you appear to take offence (or ridicule) appropriate advice underpinned with evidence from reputable sources.

"but I have"?

If you forget and clench the muscle (you're supposed to relax the muscle) before injection, it sometimes bent. If you relax the muscle just before IM, it never bends. I would then take the bent BD 30g needle and really try to break it (bend back and forth) and I could not snap the bent needle (BD 30g) - I'm a full-grown 6'7" man. I wanted to find out for my own satisfaction after the nurse who initially taught me how - she worried about the breaking of the fine 30g also. I gave her one of my BD 30g to bend and she really tried to break it off and couldn't either - she doesn't warn patients about that anymore. I have no idea what other extenuating circumstances that would make your 'snap' warning true. (eg. quality of needle - not a BD?)

wedgewood mentioned using a 30g - can you repeatedly bend and snap one of your used 30g needles? Please try to prove me wrong.

Sommerday. It doesn't matter how many times you say the same thing...it does not make it true on all occasions.

To reiterate...I will not issue advice in this forum which is contrary to both evidence based medical practice and manufacturers' instructions for use.

"it does not make it true on all occasions"

If you can get a BD 30g x 1", try to bend it repeatedly and snap it.

"risk of blow-back during the injection"??

I've never seen 'blowback', or anything remotely close.

I called a manufacturer of cyanocobalamin (when supply was restricted) and talked to a nurse. I asked about using 30g instead of 25g. She said there's no problem using 30g for cyanocobalamin - you will experience a little backpressure and only for the backpressure reason it goes in slow. And that's exactly what happens. Once again, there's no blowback whatsoever.

I'll take a little backpressure (push a little) in return for a 30g needle that's about 1/2 the diameter of a 25g. Those 25g needles look like turkey basters to me now.

Again, I'd say...you haven't seen it, I have.

Blow-back can occur precisely because of the back-pressure, which can cause the needle to become detached from the barrel of the syringe.

It's great that you feel so confident that you can advise ALL here that these things will not occur...until they do!

"which can cause the needle to become detached"??

If you don't tighten the needle on - of course, there'll be some leakage - you didn't tighten the needle to the syringe - just make sure the BD 30g needle is tight and there is only a little backpressure. A loose needle will allow some leakage with a 20g also - 30g has nothing to do with that.

If there's backpressure into muscle - it would logically follow that any 'blow-back' would also experience backpressure. And if you hit a major vein/artery to cause 'blow-back' with backpressure being exerted, you have far more problems than 'blow-back'

None of what you posited fits reality.

Try calling a B12 manufacturer and ask about using a 30g.

Sommerdaey. I really do not need a lesson from you on how to give an injection, thank you.

Point in fact (in case other readers get worried) - there are no major veins or arteries that can be damaged doing an IM injection into the thigh - no matter how much pressure is applied to a syringe plunger.

Back pressure occurs in the syringe ONLY because the B12 cannot get out of the syringe and into the muscle quickly enough - precisely because of the fine needle.

Sorry, but you need a reality check.

I think enough has been said on this topic now. Please cease and desist.

Hi I use a 25G x 5/8" needle and inject into muscle every other day as some symptoms come back if I leave it even a few hours longer. I now use my outer thighs, upper outer arms and belly in rotation. A nursing lecturer recommended the rotation as I inject so often.

Yes they'll be fine. You can get short blue needles from your local needle exchange along with 1ml or 5ml syringes and alcohol wipes. You can also return your sharps box there. Saves you having to buy them.

I'm in Scotland and you just walk in up here. It should be similar there.

Pas250218. Many apologies, but I am now closing this post to further replies.

Please be assured that this has nothing to do with the nature of your question or with the majority of the responses to you.

Please do post again if you need more help.

The ability to reply to this post has been turned off.

You may also like...