Short answer: Using a weight-loss injection pen involves these steps: letting the pen reach room temperature, attaching a new needle, setting the dose dial, inserting the needle into the skin at 90 degrees, pressing the button and waiting 6–10 seconds so the medicine is fully delivered.

Key takeaways

  • Letting a pen taken out of the fridge reach room temperature for 15–30 minutes noticeably reduces pain.
  • Always attach a new, sterile needle for every injection.
  • After pressing the injection button, wait until the counter shows 0, then count 6 seconds before withdrawing the needle.
  • Do not press on or rub the injection site; if it bleeds, press lightly with a cotton wool pad.

GLP-1 medicines are mostly given with prefilled pens. The type of pen depends on the product: some are single-use and need no dose setting, while others are multi-dose and you select the dose for each injection. The steps below describe the common process; the instructions for your own pen always take priority.

It is recommended that you do your first injection with your GP, prescriber or another healthcare professional. This page does not replace that training.

Before injecting

  • Wash your hands.
  • Take the pen out of the fridge and let it stand for a few minutes; cold liquid hurts more.
  • Check the medicine name, dose and expiry date on the label.
  • Look at the liquid: it should be clear and colourless. If it is cloudy or has particles in it, do not use it.
  • Choose the injection site: choose it knowing which site is next in line this week.

Step-by-step injection

  • Remove the pen cap.
  • Attach a new, sterile needle; a new needle is used for every injection.
  • If your pen needs a flow check (priming), do it as the instructions describe. Most single-use pens do not need this.
  • On multi-dose pens, turn the dose selector to the dose your prescriber set.
  • Insert the needle straight into the skin and hold the button down.
  • Wait for the time stated in the instructions (usually a few seconds). Withdrawing too early means part of the dose stays outside.
  • Withdraw the needle from the skin and do not rub the site.
  • Remove the needle from the pen, put it in a sharps bin and put the cap back on the pen.

Pen or vial?

Some treatments are given with a vial and syringe. In that case, the dose is read from the unit markings on the syringe, and your prescriber works out the amount. The injection technique is similar; the difference is that you draw up the dose rather than the pen doing it. Do not work out syringe units on your own.

Common mistakes

  • Pressing the button and withdrawing straight away: the full dose has not been delivered.
  • Reusing the same needle; a blunted needle increases both pain and tissue damage.
  • Taking the pen out of the fridge and injecting straight away.
  • Injecting into the same spot every week.
  • Throwing used needles away with normal rubbish.

Logging your injection

Haftra logs an injection with one tap and keeps the site, dose and time together. At your next injection, it reminds you which site is next. It does not suggest doses or work out syringe units. It is free and can be used without creating an account.

iPhone, iPad and Apple Watch. Free.

Frequently asked questions

How do you use a weight-loss injection pen?

Wash your hands, take the pen out of the fridge and let it stand for a few minutes, attach a new needle, insert the needle straight into the skin and hold the button down. Wait for the time stated in the instructions, remove the needle and do not rub the site.

Is the needle changed every time?

Yes. A new, sterile needle is used for every injection. Reusing the same needle increases pain and tissue damage, because the needle becomes blunt; it can also get blocked and carries a risk of infection.

Can I use the pen straight after taking it out of the fridge?

Take the pen out of the fridge and let it stand for a few minutes; cold liquid hurts more.

Can I withdraw the needle straight after injecting?

No. Keep the needle in the skin while holding the button down for the time stated in the instructions (usually 6–10 seconds), because withdrawing too early means part of the dose stays outside.

Will I feel pain during the injection?

The needles are very fine (31G–32G); when the medicine is at room temperature, most people feel very little pain.

Sources

  • EMA: Mounjaro (tirzepatide)
  • EMA: Ozempic (semaglutide)
  • EMA: Wegovy (semaglutide)
  • NHS: Obesity treatment
  • MHRA (Medicines and Healthcare products Regulatory Agency)

Last reviewed: 4 August 2026