How to inject Mounjaro and Wegovy — a step-by-step pharmacist guide

Before your first injection

Some practical things to set up before you open your first pen:

• Storage. Pens should be stored in the fridge (2–8°C) until first use. Don't freeze — a frozen pen must be discarded.
• A sharps bin. Used pens and needles go in a yellow sharps bin (UN3291 standard). We provide one with your first dispensing. Don't put used needles in regular household waste.
• An alcohol swab (optional but useful, particularly if you sweat a lot or your skin's been moisturised that day).
• A calendar or phone reminder for your weekly injection day. The most common cause of missed doses is just forgetting which day it is.
• The patient information leaflet (PIL) from inside the pen pack. Read it before your first injection — the brand-specific details (especially missed-dose rules) are in there.

Getting your pen ready

Both Mounjaro KwikPen and Wegovy FlexTouch / pre-filled pens are pre-mixed and ready to use. There's no mixing, drawing-up, or attaching a separate needle for either product — they're designed as single-step self-injectors.

Take the pen out of the fridge 15–30 minutes before injecting if you can; cold liquid stings more than room-temperature liquid. If you forget, it's fine — the difference is comfort, not safety.

Inspect the pen: the liquid inside should be clear and colourless or slightly yellow. If it looks cloudy, discoloured, or contains particles, don't use that pen — contact your supplier.

Where to inject — site choice and rotation

Three approved injection sites:

• Abdomen. The front of your tummy, at least 5 cm (about 2 inches) away from your belly button. Most patients find this the easiest site. Avoid the immediate navel area.
• Front or outer thigh. Middle third of the thigh, on the front or outer side. Easy to reach when sitting down.
• Back of upper arm. Possible but most people need someone else to inject for them here — it's hard to reach yourself.

Rotate sites every week. Don't inject in the same exact spot two weeks in a row. The point of rotation is to avoid skin reactions, lipohypertrophy (lumps under the skin), and inconsistent absorption. A simple rotation: week 1 left abdomen, week 2 right abdomen, week 3 left thigh, week 4 right thigh, repeat.

Avoid areas with scars, moles, broken or tender skin, stretch marks, bruises, or visible blood vessels. If a site looks irritated from a previous injection, give it 4 weeks to recover before reusing it.

Step-by-step injection technique

1. Wash your hands. Soap and water; doesn't need to be sterile.
2. Take the pen out of the fridge. Let it warm to room temperature for 15–30 minutes if possible.
3. Check the liquid. Clear, colourless or slightly yellow, no particles.
4. Choose your site. Following the rotation pattern. If using an alcohol swab, clean the area and let it dry completely (injecting through wet alcohol stings).
5. Remove the pen cap. Don't touch the needle.
6. Position the pen against the skin. 90 degrees (straight on). For thigh injections, you can pinch the skin to lift a fold; for abdomen, this isn't usually necessary in most adults.
7. Press the injection button (or twist, depending on the pen design). Hold the pen in place. You'll hear or feel a click when the injection starts.
8. Hold for 5–10 seconds. Until the full dose has been delivered — follow the PIL for the specific count for your pen. Pulling the pen out too early can mean only part of the dose has been given.
9. Remove the pen. Slowly pull it straight out from the skin.
10. Dispose of the pen. Put the cap back on (if your design allows) and place the whole pen in your sharps bin.

What if you bleed or bruise

A small amount of bleeding at the injection site is common and not a problem — press gently with a clean tissue for 30 seconds.

Small bruises happen occasionally; they're harmless and resolve over a few days. To minimise bruising: choose a slightly different sub-site within your chosen area, avoid massaging the injection point afterwards, and consider switching to a less vascular area for a week.

Persistent or large bruising, significant pain at the site, redness/warmth spreading from the site, or any sign of infection (pus, fever) needs clinical review — contact your prescriber.

What if the pen jams or doesn't work

• If the pen doesn't seem to release any liquid: don't try to force it. Contact your supplier — most defective pens are replaced.
• If you pulled the pen out too early and aren't sure if the full dose was delivered: do not take a second dose. Take your normal next dose on your normal day. Tell your prescriber so the schedule can be reviewed.
• If you accidentally inject into clothing: that's a wasted dose. Don't immediately re-inject; the dose may have partially delivered. Contact your prescriber.
• If the pen has been left out of the fridge longer than the maximum permitted (21 days for Mounjaro, 28 days for Wegovy): discard the pen and start a fresh one.

Missed-dose rules

Mounjaro (tirzepatide):

• If you remember within 4 days of your usual injection day: take the missed dose as soon as you remember, then resume your normal weekly schedule.
• If more than 4 days have passed: skip the missed dose and take the next one on your normal day.
• If you miss two or more consecutive doses, contact your prescriber — you may need to restart at a lower dose to re-establish tolerance.

Wegovy (semaglutide):

• If you remember within 5 days of your usual day: take the missed dose, then resume your normal schedule.
• If more than 5 days have passed: skip the missed dose and take the next one on your normal day.
• If you've missed two or more doses, contact your prescriber.

Never take two doses on the same day or close together to 'make up' for a missed one. The next dose should always be at least 3 days after the last to maintain proper spacing.

Changing your injection day

If your current day no longer suits you (work schedule changes, holiday, etc), both products allow you to shift the day. The rule is simple: there must be at least 3 days (72 hours) between your last injection and your new-day injection. So if you usually inject on Tuesday and want to move to Friday, that's fine — inject as normal on Tuesday, then again on Friday, then continue on Friday from then on.

If you want to move backwards (e.g. from Tuesday to Sunday), the gap is shorter and would put two doses too close together. In that case, skip the current week and start the new schedule next Sunday.

Travel handling

For trips of any length:

• Carry pens in hand luggage. Hold luggage is not temperature-controlled and may freeze. The TSA / airport security exemption for medication is well-established — you don't need a separate letter to carry pens, but having a copy of your prescription is wise.
• Temperature control. An insulated pen pouch with a small cool pack works for journeys up to a day. For longer trips, plan refrigeration at the destination. The pen tolerates up to 30°C for a defined number of days (21 for Mounjaro, 28 for Wegovy) so room temperature is fine for most trips.
• X-ray scanners. Pens can go through standard airport security X-rays without issue.
• Doctor's letter. Optional but reassuring if you're carrying multiple pens or travelling internationally. Your prescriber can provide one.
• Time zone changes. Stick to your usual injection day in the destination time zone; the underlying weekly rhythm doesn't need to shift.

First injection — the nerves

Almost everyone's first injection feels harder than the second. A few practical tips:

• Don't watch the needle as it goes in; look at the pen body or your hand. The visual makes it feel more significant than it is.
• Breathe out as you press the injection button. The relaxation makes the moment shorter.
• Sit somewhere comfortable, not standing in the kitchen feeling rushed.
• Have someone with you the first time if it helps — a partner, family member, or in our case, a pharmacist for the in-clinic first-injection support if that's part of your programme.
• Once it's done, you'll know how easy it was. Most patients report the second injection felt completely different from the first.

Special situations

Illness. If you're acutely unwell (vomiting, severe diarrhoea, significant fever) on your injection day, talk to your prescriber before injecting. In most situations the dose can be delayed safely until you've recovered.

Planned medical procedure. If you have a scheduled procedure involving anaesthesia or significant fasting, discuss with the procedural team in advance — there may be guidance to pause the medication for a specific period beforehand because tirzepatide and semaglutide slow gastric emptying.

Pregnancy. Do not continue injecting if you become pregnant. See our contraception guide for the planning side.

Switching between products. If you're switching from Wegovy to Mounjaro or vice versa, see our switching guide for the planned-gap protocol.

Disposal

Used pens with the needle attached are classed as sharps waste. They go in a UN3291-standard yellow sharps bin. When the bin is roughly three-quarters full, return it to your supplier (we accept full sharps bins back at the pharmacy) or, in some areas, your council collects domestic sharps waste — check your local council website.

Don't put used pens in regular household bins, recycling, or down the toilet. Don't decant the needles into other containers.

How this fits with the wider programme

Injection technique is the easiest part of weight management with Mounjaro or Wegovy. The harder parts are the dose-escalation choices, the food and behaviour scaffolding, side effect management, and (for some patients) contraception planning. For the broader picture see our Mounjaro explainer, Wegovy explainer, month-by-month side effects guide, and contraception guide.

The next step

If you'd like to do your first injection with a pharmacist alongside you for confidence, that's something we offer in clinic on the day you start. Book a starter consultation and we'll cover the pen, the technique, your missed-dose plan, your storage at home, and the first-week side effect playbook.