CommunityInjection Technique

4mm vs 6mm pen needles

38 replies23 peopleJul 6, 2026☆ Follow
Summary

4mm or 6mm pen needles for subcutaneous injections with hidden-needle pens?

Users report mixed experiences with needle lengths for twice-weekly peptide injections. Some find 4mm sufficient and less noticeable, especially on the abdomen, while others prefer 6mm to reduce injection-site reactions or ensure proper depth with the cap in place. Several note that 4mm works fine for most sites but may require pinching or careful technique, and one manufacturer reference indicates shorter needles reach the target layer without folding skin.

What this discussion establishesWhere people disagree

Whether 4mm is reliably long enough with the pen cap engaged, and whether shorter needles increase ISRs for everyone.

Still open

Individual variation in skin thickness, site choice, and sensitivity means no single length suits all users or compounds.

Nothing here is advice.

38 replies · 23 people
PlainMarble21archiveopening postJul 6

I've been doing reta injections twice a week for two months and it still feels just as hard. My husband has been doing them for me since I'm too nervous to do it myself. I bought a pen designed for hidden needles and now I'm looking at 33-gauge 4 mm tips but wondering if 6 mm would be better instead. I'm carrying extra weight so there is plenty of fat to work with. Will the shorter ones still reach the right layer when the cap is on?

GreenMeadow27archiveJul 6
↳ replying to @PlainMarble21 (opening post)

I'd go with the longer option. Shorter needles seem to come with a higher chance of reactions at the site.

KeenFenwick81archiveJul 6

I'd pick the 6 mm size as well. Also check that the tips you buy are compatible with the pen so the hiding cap still works properly.

PatientTimber12archiveJul 6
↳ replying to @GreenMeadow27

That's a shame. I already bought a whole box of the shorter ones. I'll still try them since they will probably work okay anyway. Live and learn.

SlowSparrow49archiveJul 6
↳ replying to @KeenFenwick81

The regular version of those tips can be used, just not the plus version. I learned that the hard way. I would have chosen the longer size too. If the short ones end up being too shallow you can still use them for purging cartridges after filling, or try them without the cap.

QuietThistle70archiveJul 6

I use the shorter ones on the stomach and the longer ones on the rear. On the belly I can pinch better and line things up more easily. Results will vary by person.

LevelAlder29archiveJul 6
↳ replying to @PatientTimber12

Same here. I received samples in several lengths with a new pen kit and the shortest ones felt really comfortable, especially on the arm. I ordered a large box of them. No site reactions when using them with another compound. I kept the longest ones for rear injections.

NorthQuill51archiveJul 6
↳ replying to @PatientTimber12

You may already know this, but some pens from one major maker come with the shortest needles. They must have a reason. Still, my feeling is that anything from 4 to 8 mm works fine. The shorter ones also don't need you to pinch the skin.

PatientTimber12archiveJul 7
↳ replying to @NorthQuill51

I didn't realize that. Useful information.

GreyAlder39archiveJul 7

According to one pen maker's diagram and notes, the shortest lengths reach the correct layer automatically. At 6 mm you need to fold the skin. At 8 mm you should go in at an angle to avoid going too deep. Going into muscle can cause problems because of blood vessels and different diffusion, and there's even a small risk of damaging the fascia with larger volumes. My usual choice is 32-gauge 4 mm from one brand; for 1 ml syringes I use 31-gauge 6 mm.

IronLantern24archiveJul 7

I have the same brand in three different lengths. I save the longest for the more irritating compounds and use the others for everything else. I think the shortest ones can be too shallow unless the skin at the site is fairly thin. Once these run out I plan to stay with the middle or longest size.

PlainMarble21archiveJul 7
↳ replying to @SlowSparrow49

I'd like the shortest 33-gauge ones but they all seem to be the plus version. What exactly prevents them from working with the pen?

PatientFenwick91archiveJul 7

Not a fan of the shortest size. The shortest I'd consider is 5 mm. The middle length works perfectly every time.

ClearMeadow73archiveJul 7

I have the shortest ones for two compounds and the longest for anything containing a certain copper peptide. I only ordered the short box because that was what came with a prescription version before. After this box I'll try the longest and switch to middle if needed.

SteadyWillow88archiveJul 7
↳ replying to @GreyAlder39

This matches what I do and I've stayed with the shortest size for a long time. I'm really happy with a European brand of 4 mm 32-gauge needles; I barely notice them going in.

SlowBramble67archiveJul 7
↳ replying to @PlainMarble21 (opening post)

The middle lengths work much better when the cap is on. I don't recommend using the cap at all though, because the needle can bend if you don't hit it at the right angle.

GreyAlder39archiveJul 7
↳ replying to @SteadyWillow88

Thanks. Six bevel and silicone coated sounds worth trying even if it costs more than the usual ones.

SlowSparrow49archiveJul 7
↳ replying to @PlainMarble21

The regular version has a smaller base. The plus version is too wide to fit through the hole in the cap. You could still use it without the cap, but not with it.

KeenHarbour15archiveJul 15
↳ replying to @ClearMeadow73

Why do you choose the longest size for anything containing that copper peptide?

BlueAlder28archiveJul 15
↳ replying to @KeenHarbour15

Injecting deeper reduces the stinging from that compound. That's why I use the longest size. Diluting it a lot also helps. I don't like one particular brand because I've bent quite a few of their longer 32-gauge tips. I prefer another brand's 31-gauge longer ones but will probably move to the middle length for most things except that copper peptide when I reorder.

PatientSparrow94archiveJul 15
↳ replying to @NorthQuill51

I'm not sure which company ran it, but one maker tested longer versus shorter needles in people with more body fat and found no difference in how fast the GLP compounds were absorbed. Most participants didn't feel the shortest ones at all, which is probably why they supply them.

NorthSparrow68archiveJul 15

One thing I've noticed is that the shortest needles feel a bit shallow for the compounds that tend to burn. The middle length seems to place the dose below the layer that gets most irritated. Your experience may differ.

PatientAlder89archiveJul 15

I like the shortest 32-gauge because I'm sensitive and don't want to feel anything.

PlainMarble21archiveJul 15

I've now tried the middle-length 32-gauge from one brand twice and I can definitely feel it. My husband and son don't notice it at all. Not sure why it affects me differently.

GreyAlder39archiveJul 15
↳ replying to @PlainMarble21

Try areas with fewer nerve endings such as the sides of the waist or the upper part of the buttocks. If your skin has loosened after weight loss, use the folds that form. Otherwise pinch a fold before inserting. You can also test whether breathing in or out changes how it feels.

IronFenwick84archiveJul 15
↳ replying to @PlainMarble21

I read somewhere that coughing at the moment of injection helps block the sensation. It works for some people.

PlainMarble21archiveJul 16
↳ replying to @IronFenwick84

I don't want to shift position and make it worse by accident!

IronFenwick84archiveJul 16
↳ replying to @PlainMarble21

It will get easier with time. It sounds like you really want to keep going, so stick with it.

PlainMarble21archiveJul 16
↳ replying to @IronFenwick84

I've been doing the twice-weekly shots since early May and it still hasn't become any easier. If anything my anxiety has increased, but I'm at a point where I really need to continue. A fear of blood and needles seems to run in my dad's family, though it shows up differently in each of us. Exposure is supposed to help but I'm still waiting for results.

PatientAlder89archiveJul 16
↳ replying to @PlainMarble21

Have you tried icing the area first? I still do it months later because I'm sensitive too. I also wear headphones with calm music, close my eyes, and try to relax.

RustBramble70archiveJul 16
↳ replying to @LevelAlder29

It really comes down to the person you're speaking with at the moment.

PlainMarble21archiveJul 16
↳ replying to @PatientAlder89

Do you clean the skin before or after icing? I tried icing once but by the time the alcohol dried the numbing effect seemed to be gone.

GreenPebble54archiveJul 16

I use the shortest size even for the copper peptide and rarely feel any sting. Pinning does become easier over time. Doing it myself and watching the motion helped a lot. A smooth, steady movement reduces pain while hesitating lets your mind take over.

PatientAlder89archiveJul 16
↳ replying to @PlainMarble21

I ice for fifteen to twenty minutes with a reusable pack. I take it off right before the shot, then wipe with alcohol so the skin is clean at the last moment. The cold lingers for a while afterward.

SteadyWillow88archiveJul 17
↳ replying to @KeenHarbour15

I have a collection of different pens, including one brand from Europe and a modified version of another model. As someone outside the US I ordered them from overseas.

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