How to use your GLP-1 pen correctly
General steps, injection sites, storage and common mistakes. Always follow the instructions in your medication leaflet and your doctor's guidance.
General injection steps
Although each pen has small differences, the basic process is similar for Ozempic, Wegovy, Mounjaro and Saxenda:
- Wash your hands and check that the liquid is clear and colourless. If you see particles or it looks cloudy, do not use it.
- Prepare the needle. For multi-dose pens (Ozempic, Saxenda), attach a new needle. For single-dose pens (Wegovy, Mounjaro), the needle is built in — check the seal is intact.
- Clean the site with an alcohol swab and let it dry.
- Gently pinch the skin and insert the needle at a 90° angle.
- Press the button and keep the needle in for 5 to 10 seconds. For Mounjaro, wait until you hear two clicks; for Ozempic, hold at least 6 seconds after the dose counter shows zero.
- Remove the needle and dispose of it in a sharps container. Never throw it in household waste.
Injection sites
There are three approved sites for GLP-1 pens:
- Abdomen: at least 5 cm (2 in) from the navel, avoiding the midline.
- Front of the thigh: in the middle area, avoiding the inner thigh.
- Back of the upper arm: you may need someone to help you inject here.
Why rotate?
Injecting in the same spot repeatedly can cause lipodystrophy (hardening or pitting of fatty tissue) and, rarely, cutaneous amyloidosis. Both affect how the medication is absorbed. André automatically suggests the site that has gone the longest without use — so you rotate without having to keep track. If you use Mounjaro, see our Mounjaro Tracker page for body map and automatic rotation.
Storage
Conditions vary by medication. As a general rule:
- Before opening: refrigerate (2–8 °C / 36–46 °F). Never freeze.
- After opening: room temperature (up to 30 °C / 86 °F) for a limited number of days.
Specific out-of-fridge times after first use:
- Ozempic: up to 56 days.
- Mounjaro: up to 21 days.
- Wegovy: single-dose, use immediately.
- Saxenda: up to 30 days.
Never expose the pen to direct sunlight or extreme temperatures. If it has been frozen, do not use it.
What if you miss a dose?
- Ozempic / Wegovy (weekly semaglutide): if fewer than 5 days have passed, inject it. If more than 5 days, skip it and take the next one on your regular day.
- Mounjaro (weekly tirzepatide): if fewer than 4 days (96 h) have passed, inject it. Otherwise, wait for the next dose.
- Saxenda (daily liraglutide): take your next regular dose. Do not double up. If you have missed more than 3 days, restart the titration from 0.6 mg.
Never take a double dose to make up for a missed one.
Common mistakes
- Injecting in the same spot every time.
- Leaving the needle on the pen between uses (can cause air bubbles and inaccurate dosing).
- Using a pen that has been frozen or has exceeded its out-of-fridge time.
- Mounjaro-specific: replacing the grey cap after use (damages the mechanism).
- Storing the pen with the needle attached between injections.
When to call your doctor
- Severe or persistent stomach or back pain (may indicate pancreatitis).
- Swelling of the throat or tongue, difficulty breathing (allergic reaction).
- Sudden changes in vision.
- Lump or swelling in the neck, hoarseness, or difficulty swallowing.
- Severe dehydration from persistent vomiting or diarrhoea.
More detail on digestive side effects in our guide on nausea and when to call your doctor.
Related guides
- Nausea: what's normal and when to consult — the most common side effect and how to manage it.
- What to eat during GLP-1 treatment — gentle foods, plate structure and nutritional gaps.
- 8 GLP-1 myths — what the science says about the most common claims.
Sources: FDA prescribing information for Ozempic (2025), Mounjaro (2022), Wegovy (2021) and Saxenda (2020); Mayo Clinic Diet; NHS semaglutide; Lilly Mounjaro instructions for use.