Top 6 Injection Mistakes

By Ari
published 2026-10-21

[printable foldable PDF version][web PDF version]

Top 6 Injection Mistakes

Boba tea cup with large straw.

(and how to avoid them)

Incorrectly opening the vial top (… or not!)

If your vial has a small metal disk covering the stopper, do remove that before drawing…

Picture of unopened vial stopper with a needle puncture through the metal cap, with a large red X mark superimposed in the corner. Red X mark

Picture of vial with the metal stopper peeled and ripped all the way to its side, exposing the side of the rubber stopper underneath, with a large red X mark superimposed in the corner. Red X mark

But don’t remove the entire metal cuff holding the stopper in place!

How to correctly expose the stopper:

Four pictures of a vial showing in four steps on to correctly and gently pry off the metal cap without damaging the stopper, with a large green checkmark superimposed in the corner. Green checkmark

Improvisational vial cleaning

Don’t clean your vial top with:

  • hand sanitizer
  • bleach
  • iodine
  • water
  • 100% alcohol

Red X mark

or anything else other than…

Illustration of bad things to swab vial with, showing a faucet with running water, a hand sanitizer bottle, and a box of iodine swab sticks, with a large red circle with red cross bar superimposed over them.

70% ethanol or isopropanol prep pads!1

Picture of a box of alcohol prep pads

Illustration of hand wiping vial top with alcohol prep pad, with a large green checkmark superimposed in the corner. Green checkmark

If you’re out of prep pads, it’s better to just skip vial cleaning this time.

Piercing the vial with a boba straw needle

Although many guides recommend it, don’t use 18G needles to draw from your vial.

Boba tea cup with large straw. Red X mark

These recommendations originally derive from research conducted in healthcare settings, where clinicians administer several injections per day to different patients.

In those settings, medication vials get used up very quickly and it makes sense to use a large needle to prioritize drawing speed. But for trans people who use one vial for a span of months or even years, we need to take better care of our vial stoppers than that! A busted stopper compromises your vial’s ability to stay sterile.

Studies of how many punctures a vial can withstand have found that needles of 22G or smaller cause much less damage than larger needles.2

Box of 23G x 1" needles, with a large green checkmark superimposed in the corner. Green checkmark

Remember: bigger gauge (G) = smaller needle!

Sterilizing your sterile needles

Yes, Trace Lysette did it in the movie Monica.

That doesn’t mean it’s a good idea!

Needles are sterile out of the package.

As long as the packaging hasn’t been damaged, you’re good to go as soon as you unwrap it. Swabbing the needle with something only introduces more potential contaminants to both your vial and your body!

Picture of the front and back of a sterile needle in its wrapping.

Illustration of a hand mistakenly swabbing a sterile needle with an alcohol pad with a red circle and red bar superimposed over it.

For insulin needles that come in multiple per bag, a bright orange cap should be covering the needle and plunger. These keep them sterile too!

Picture of a box and a bag of insulin syringes with fixed needles.

Misreading the markings on your syringe barrel

Make sure to read the units on your syringe barrel carefully. The dose is measured from the top of the plunger.

Picture of a 1mL Luer syringe with an arrow pointing at the the total volume inscription at the end of the barrel, labeled "Total Volume", and a second arrow pointing at the measurement markings along the barrel.

Close-up picture of the barrel of a syringe partially filled with oil with the plunger between the 12th and 13th small marks, indicating the barrel is filled with 0.125 mL of oil.

0.1mL is a small amount of liquid in most syringes. Don’t give yourself 10x as big of a dose by mistake!

For people who inject 0.1mL or less, insulin syringes come in 0.5mL and 0.3mL sizes and can be used for subcutaneous injection. It’s easier and more accurate to use these smaller syringes for small doses.

Picture of a 0.5 mL U-100 insulin syringe, with an arrow point where to locate the inscription showing the type of units on the syringe barrel, in this case U-100, indicating that each small marking is equivalent to 1 mL / 100 = 0.01 mL, and a second arrow pointing along the barrel at the 20 unit mark, indicating that pulling the plunger down to that point equals drawing 20 x 0.01 mL = 0.2 mL.

Insulin syringe markings measure insulin units.

1 mL = whatever the U number is.

For instance:

On a U-100 syringe, 100 units = 1 mL, so 10 units = 0.1 mL

On a U-40 syringe, 40 units = 1 mL, so 10 units = 0.25 mL

Tossing out your dose when swapping needles

Detachable needles and syringes always have some space that the plunger can’t fully push liquid out of, called deadspace.

Illustration showing four types of syringe and needle hubs: (1) Standard syringe with standard detachable needle, high amount of deadspace (typically 92 uL = 0.092 mL) (2) Modified syringe with standard detachable needle, rubber plunger with narrow tip extending into the hub to push liquid out of the deadspace, reduced amount of deadspace (typically 59 uL = 0.059 mL) (3) Standard syringe with low deadspace needle, the inside of the needle hub has a narrow point which extends into the syringe hub to fill the deadspace (deadspace as low as 17 uL = 0.017 mL) (4) Low deadspace insulin syringe with fixed needle (deadspace typically 3 uL = 0.003 mL). Credits: exchangesupplies.org Low Dead Space Injecting Equipment: A Briefing

When swapping needles, make sure to draw in air before removing the drawing needle so you don’t lose your dose to the needle deadspace! It’s also possible to use air to flush out deadspace after injecting, a technique called airlocking.

Resources

US-based needle suppliers

needle info + how-to videos

* note that this guide makes the bad recommendation of using 18G needles to draw! ignore that, it will core your vial. otherwise it’s a great resource.

find local needle exchanges in the US

needle disposal information by US state

  1. Why 70% Ethanol is the Star of Sterilization: Mechanisms and Limitations↩︎

  2. Ponto, J. A. (2013). Self-sealing capacity of vial stoppers after multiple needle punctures. Journal of the American Pharmacists Association: JAPhA, 53(1), 58–60. https://doi.org/10.1331/JAPhA.2013.12064↩︎