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Needle length for using insulin syringes with Mounjaro pens?

11 replies

PuzzledObserver · 09/09/2026 08:14

Just finished my first 2.5mg Mounjaro pen, 5mg pen on the way this week. Have bought extra needles and swabs to facilitate short dosing/extending pen usage - but also have a golden dose in my existing pen, and have had some thoughts about possible contamination risk if using a higher dose pen for many weeks.

So, thinking bout going the insulin syringe route. What length of needles do people use for those? The pen needles I was supplied with are 4mm, so that’s what I’ve bought more of to use with the pens. But are those sufficient if using an insulin syringe to extract the dose from the pen?

OP posts:
SilenceInside · 09/09/2026 08:24

You can use 4, 6 or 8mm needles. I use 8mm ones as I find the length helpful when extracting. I haven’t tried 4mm ones. Logically they should be fine as the red seal isn’t going to be more than 4mm in depth I’d have thought looking at it.

MJqueen · 09/09/2026 08:40

You can get the same screw in needles from any pharmacy, then count clicks for partial doses. I think mine are 6mm. They won’t work for the bonus dose unless you keep twisting and manage to break the pen. I have some syringes from Amazon for that, although now that the new pens are only 4 doses they will soon be redundant.

PuzzledObserver · 09/09/2026 11:41

SilenceInside · 09/09/2026 08:24

You can use 4, 6 or 8mm needles. I use 8mm ones as I find the length helpful when extracting. I haven’t tried 4mm ones. Logically they should be fine as the red seal isn’t going to be more than 4mm in depth I’d have thought looking at it.

I had wondered whether you need a longer needle for extracting. Do you feel any difference when injecting?

OP posts:
SilenceInside · 09/09/2026 11:46

The needle itself feels the same, it's the gauge that would make a difference rather than the length. As long as the gauge is 30 or 32g then they will be just like the pen needle. It's easier to inject with a syringe as you aren't dealing with the more substantial pen mechanism which can be quite hard to push down.

MrsMiagi · 12/09/2026 22:19

4mm is fine, thats what i use

KizzyKoala · 14/09/2026 21:04

Can anyone link to 4 or 6mm syringe needles from a reputable and tested source please?

MJqueen · 15/09/2026 23:38

KizzyKoala · 14/09/2026 21:04

Can anyone link to 4 or 6mm syringe needles from a reputable and tested source please?

Mine are from Amazon. I’ve been on MJ for 2.5 years and haven’t died yet so they are probably fine…

Like this - https://amzn.eu/d/07j8JlVy

Amazon

Amazon

https://amzn.eu/d/07j8JlVy?tag=mumsnet&ascsubtag=mnforum-weight-loss-injections-5576439-needle-length-for-using-insulin-syringes-with-mounjaro-pens

Ketra · 16/09/2026 09:12

KizzyKoala · 14/09/2026 21:04

Can anyone link to 4 or 6mm syringe needles from a reputable and tested source please?

I buy from UK Medi - I use 8mm so don't have a link to the ones you are looking for but it's very easy to search there.

There are a lot of other reputable medical companies out there - I would just avoid Amazon and ebay - I know some people are comfortable doing that but personally I think it's too risky.

HappyWineDay · 17/09/2026 07:21

MJqueen · 15/09/2026 23:38

Mine are from Amazon. I’ve been on MJ for 2.5 years and haven’t died yet so they are probably fine…

Like this - https://amzn.eu/d/07j8JlVy

It says they are for “lab use only” - that’s not for injecting people. I’d recommend you use UK Medi and get approved human-use syringes.

Freecall · 17/09/2026 16:58

HappyWineDay · 17/09/2026 07:21

It says they are for “lab use only” - that’s not for injecting people. I’d recommend you use UK Medi and get approved human-use syringes.

That is because Amazon stopped retailers on their site selling medical supplies a couple of years ago so the companies now list them as 'lab equipment' or 'measuring tools'.

They are exactly the same syringes that we have used for years though.

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