Both Mounjaro and Wegovy are given as a once-weekly subcutaneous (under the skin) injection, using a pre-filled pen designed for self-administration. The general process is the same regardless of which medicine you're on: wash your hands, check the pen and medicine look right, choose and clean an injection site (stomach, thigh, or upper arm if someone else is injecting you), inject following your specific pen's mechanism, hold it in place for the count specified in your leaflet, then dispose of the needle safely in a sharps bin. The exact button or dial mechanism differs between pen types and has changed over different product versions, so always follow the Instructions for Use that comes in your own pack rather than relying on general instructions alone.
Mounjaro and Wegovy use different pen platforms, and even within each brand, the exact design has evolved across doses and product updates. Before your first injection, it's worth knowing broadly what to expect — but always check the leaflet in your specific pack, since assuming the wrong mechanism is one of the most common sources of injection anxiety.
| Mounjaro (KwikPen) | Wegovy (FlexTouch) | |
|---|---|---|
| Needle | Often pre-attached, single-use auto-injector | May require attaching a separate pen needle, depending on your specific pen and dose |
| Dosing | Fixed dose per pen, set by your prescription | Fixed dose per pen; some earlier pen versions contain multiple weekly doses in one pen |
| Mechanism | Press-and-hold style injection | Varies by version — some are press-button, some require dialling a dose before injecting |
Worth knowing
If anything about your pen doesn't match what you expected — a dial instead of a button, a needle you need to attach yourself, or a different dose count — that's not necessarily a fault. Pen designs vary by dose and have changed over time. Check the leaflet in your specific pack, and if you're still unsure, ask your pharmacist for a walkthrough before you inject.
- Take your pen out of the fridge around 30 minutes before your injection — injecting cold medicine tends to sting more than medicine that's closer to room temperature
- Wash your hands thoroughly with soap and water, or use an alcohol-based hand sanitiser
- Check the pen: confirm the medicine name and dose match your prescription, check the expiry date, and look through the inspection window — the liquid should be clear and colourless to slightly yellow, with no cloudiness or visible particles
- Never use a pen that has been frozen, dropped, or looks damaged in any way
- Gather what you need: the pen, a new needle if your pen requires one, an alcohol wipe, and a sharps disposal container
Both medicines are injected subcutaneously, meaning into the layer of fat just under the skin, in one of three general areas.
- Stomach (abdomen) — at least 2 inches (5cm) away from your belly button
- Front of the thigh
- Back of the upper arm — only if someone else is giving you the injection, as this area is hard to reach yourself
Whichever area you choose, rotate your exact injection point each week rather than using the same spot repeatedly. Injecting in the same precise location can lead to skin changes, lumps or discomfort over time. A simple rotation pattern many people find easy to remember is to move systematically around one body area (for example, working around the abdomen in a clock pattern) before moving to a different area the following month.
- Leave at least 2cm (roughly an inch) between this week's injection site and last week's
- Avoid injecting into scars, stretch marks, moles, or areas of skin that are bruised, red, hard, swollen or tender
- Clean your chosen site with an alcohol wipe or soap and water, and let it air dry before injecting — don't blow on it to speed this up
The exact button-press or dial mechanism varies between pen types, so the steps below describe the general process common to both — always follow the specific numbered steps in your own pen's Instructions for Use for the precise technique.
1. Remove the pen cap and set it aside on a clean surface — don't put the cap back on the needle once it's been exposed.
2. If your pen requires a separate needle, attach a new one following the instructions in your leaflet, and remove both the outer and inner needle caps before injecting.
3. Hold the pen against your cleaned injection site at the angle specified in your leaflet (this is typically straight down, at 90 degrees, for most current pen types).
4. Press the injection button, or follow your pen's specific dialling and plunging steps, and hold the pen firmly in place for the full count given in your Instructions for Use — typically several seconds — even after you feel the injection has finished.
5. Remove the pen or needle from your skin. If you see a small amount of blood, press a cotton ball or gauze gently against the site without rubbing.
6. Dispose of the needle immediately in a sharps container — never leave a used needle attached to the pen, and never place it directly in household waste.
Important
Never share your pen with another person, even if you attach a new needle each time. Sharing an injector pen carries a real risk of passing on blood-borne infections, because the internal mechanism can still come into contact with your blood. Each pen is for one person only.
| Before first use | After first use | |
|---|---|---|
| Storage | Refrigerate at 2–8°C | Room temperature, below 30°C, away from direct heat and light |
| Typical shelf life once opened | — | Around 28–30 days, depending on your specific pen — check your leaflet for the exact figure |
| Never | Freeze the pen | Use a pen that has been frozen, exposed to direct sunlight, or dropped |
If you're travelling, an insulated bag or cool pouch (without direct contact with ice) helps keep your pen within a safe temperature range. If you're ever unsure whether a pen has been stored correctly — for example, if it's been left in a hot car or a delivery was delayed in transit — don't use it, and contact your pharmacist for advice rather than guessing.
Used needles and pens should never go into your household rubbish or recycling. You have a few safe options:
- Use a proper sharps disposal container, available from your pharmacy
- Many pharmacies, including Happy Pharmacy, and some GP surgeries offer needle disposal services — ask what's available locally
- If a sharps container isn't available immediately, a sturdy plastic container with a secure, tight-fitting lid (such as a laundry detergent bottle) can be used temporarily, clearly labelled, until you can dispose of it properly
The exact guidance on missed doses differs slightly between Mounjaro and Wegovy, and depends on how many days have passed since your missed dose — for the specific timings for your medicine, see our dedicated dose schedule guides. As a general principle: if you catch a missed dose within a few days, you can usually take it as soon as you remember; if it's getting close to your next scheduled dose, most guidance is to skip the missed one and simply resume your normal weekly schedule, rather than doubling up. If you're ever unsure, contact your prescriber or pharmacist rather than guessing — taking two doses close together is not recommended.
Never Injected Before? We're Here to Help.
Every new patient at Happy Pharmacy gets clear injection guidance from our GPhC-registered pharmacy team alongside their prescription — so you're never left to figure it out from a leaflet alone.
Start Your Free Online Consultation → Use code SWITCH10 if you're switching from another providerHappy Pharmacy is a GPhC-registered pharmacy (No. 9012585) — Superintendent Pharmacist: Palvinder Deol — Rated 4.8★ Excellent on Trustpilot
- electronic Medicines Compendium (emc). Mounjaro KwikPen — Instructions for Use and Patient Information Leaflet.
- electronic Medicines Compendium (emc). Wegovy FlexTouch — Instructions for Use and Patient Information Leaflet.
- Eli Lilly. Mounjaro KwikPen Instructions for Use.
- Novo Nordisk. Wegovy FlexTouch pen user guide.