First, know which pen you have: weekly or daily
If you remember one practical fact about weight-loss injections in the UK, make it this: Wegovy and Mounjaro are once-weekly pens; Saxenda is a once-daily pen.[1][2][3] Almost every routine question comes back to that one difference.
| Pen | Device | Schedule |
|---|---|---|
| Wegovy (semaglutide) | FlexTouch pre-filled pen holding four once-weekly doses; each pack includes 4 disposable NovoFine Plus needles[1] | Once weekly[1] |
| Mounjaro (tirzepatide) | KwikPen (multi-dose, 4 doses of 0.6 mL per pen) or single-dose pre-filled pens[2] | Once weekly[2] |
| Saxenda (liraglutide) | Multi-dose pre-filled pen[3] | Once daily, at any time, with or without meals[3] |
The device line-up changes over time: the MHRA approved a single-dose 7.2 mg Wegovy pen on 14 April 2026, delivering the highest maintenance dose in one injection instead of three.[4] If your pharmacy hands you a different-looking device, read the leaflet inside. For what is in each device, see our Mounjaro pen guide and Wegovy pen guide. These pens are sometimes called "skinny jab pens" online — treat the nickname with caution, because it usually signals an unregulated source rather than a pharmacy.
Where the injection goes: sites and rotation
All three licensed pens are injected subcutaneously — into the layer of fat just under the skin, never into a vein or a muscle; the Saxenda SmPC is explicit about this (subcutaneous only).[3] The Wegovy and Mounjaro labels both name three injection areas: the abdomen, the thigh or the upper arm.[1][2] For Saxenda, follow the site diagrams in the leaflet in your box.
Within those areas, vary the exact spot each time — the Mounjaro SmPC, for one, tells patients to rotate injection sites.[2] Injection-site reactions are listed among the common side effects of both Mounjaro and Saxenda,[2][3] so give each patch of skin time to recover. Your leaflet includes site diagrams; if you are new to injecting, ask a pharmacist or nurse to walk you through the first one.
Needles and hygiene
- A fresh needle for every injection. The needles supplied with these pens are disposable — the Wegovy pack includes four NovoFine Plus needles, one for each of the pen's four weekly doses.[1] Attach a new one before you inject, and take it off afterwards. Never store the Mounjaro KwikPen with a needle still attached.[2]
- Never share a pen, even with a new needle fitted — a multi-dose pen is a single-patient device.
- Clean hands, clean skin. Wash your hands, and inject into clean, unbroken skin; avoid bruised or tender spots.
- Follow the leaflet's checks before injecting. If anything looks wrong, ask your pharmacist rather than pressing on.
Storage: the fridge, and the in-use window
Storage is where the three pens are most alike. Before first use they all live in the refrigerator at 2–8 °C, and none may ever be frozen.[1][2][3] Once in use, each label allows a limited spell out of the fridge — the "in-use window" — after which the pen is discarded even if medicine remains inside.
| Pen | Before first use | Once in use |
|---|---|---|
| Wegovy | Refrigerate at 2–8 °C in the original carton; do not freeze[1] | The label permits a short spell at higher temperature — we deliberately do not quote a number; check your leaflet or the SmPC for the exact days and temperature limit[1] |
| Mounjaro | Refrigerate at 2–8 °C; do not freeze[2] | According to the emc summary, may be kept unrefrigerated at not above 30 °C for up to 30 days after first use, then discarded[2] |
| Saxenda | Refrigerate at 2–8 °C; do not freeze[3] | Can be kept for 1 month below 30 °C or in the fridge; keep the cap on to protect from light[3] |
Every one of these labels says the same thing: do not freeze.[1][2][3] Freezing is not a recoverable mistake. If a pen might have frozen, do not inject it — take it to your pharmacy and ask.
Travelling and flying with a pen
The storage rules above are the whole logic of travel: never freeze, and once in use the Mounjaro and Saxenda labels cap the pen at around 30 °C.[2][3] So keep the pen with you, in your hand luggage, where you control the temperature — not in checked baggage or a parked car, where you control nothing.
- Carry pens in the original carton with the pharmacy dispensing label, so what you are carrying is self-explanatory.
- For long journeys or hot destinations, ask your pharmacist about a cool bag — and how to use it without freezing the pen against an ice block.
- Ask how to handle dose timing across time zones; the answer differs between a daily pen and a weekly one.
- Plan supply with your prescriber before the trip; sellers outside a regulated pharmacy are where counterfeit and mishandled stock enters the picture.
Needle and pen disposal: ask before your first injection
This page deliberately does not print a disposal routine, because the right answer depends on two things this site cannot see: the disposal instructions in your own pen's patient information leaflet, and the local arrangements where you live. What we can tell you is exactly where to get that answer:
- Read the disposal section of the leaflet in your box. It is written for your specific pen and the needles supplied with it.
- Ask the pharmacy that dispenses your pens two questions before your first injection: how should used needles be disposed of, and what should happen to the pen itself once it is finished?
- Ask who handles things where you live — your pharmacist can tell you whether your GP surgery or local council plays a part in the arrangement, and how any container you are given gets collected or replaced.
The reason to ask in advance is simple: the moment to learn the routine is before your first injection — not afterwards, improvising with a used needle in your hand.
Missed doses: why we point you to the leaflet
This page deliberately does not print a missed-dose rule for each pen. The correct action depends on which medicine you use and how late you are — the rule for a once-weekly pen like Wegovy or Mounjaro[1][2] is not the rule for once-daily Saxenda.[3] Applying the wrong pen's rule is worse than none, so check the one document always right for your box: your own patient information leaflet.
The principles that hold for all of them:
- Do not inject anything extra to catch up until you have checked. If you are tempted to double up after a missed dose, stop — read the leaflet, or phone the pharmacy, before injecting anything at all.
- Check the leaflet first, then ask a pharmacist — a call to the dispensing pharmacy settles most missed-dose questions quickly.
- Make the schedule hard to fumble. Give a weekly pen a fixed day and a reminder; Saxenda is once daily at any time,[3] but works best tied to a daily anchor.
When to call a pharmacist or GP
Most day-to-day pen questions are pharmacist territory, no appointment needed. But some situations need prompt medical advice:
- Severe, persistent stomach pain. Acute pancreatitis has been reported with these medicines, and treatment is stopped if it is suspected[2] — seek help promptly.
- Vomiting or diarrhoea you cannot stay on top of. Fluid loss can lead to dehydration and, rarely, to deterioration in kidney function.[1]
- Possible gallstone symptoms. Gallbladder problems (gallstones and gallbladder inflammation) are reported across this class of medicines.[3]
- Low blood sugar, if you also take diabetes medicines. Hypoglycaemia risk increases when these pens are combined with insulin or a sulphonylurea, and those doses may need adjusting[2] — by your prescriber, not you.
- Pregnancy, or planning one. These medicines should not be used during pregnancy[1] — contact your prescriber promptly.
If you think a weight-loss pen has caused a side effect — even one not in the leaflet — report it through the MHRA's Yellow Card scheme and tell your GP or pharmacist. Patient reports are part of how the UK's medicine-safety system works. For how often side effects occur, see our side effects page.
Frequently asked questions
Where do you inject a weight-loss pen?
Under the skin (subcutaneously), never into a vein or muscle.[3] The Wegovy and Mounjaro labels name the abdomen, thigh or upper arm as injection areas;[1][2] for your own pen, follow the site diagrams in its leaflet. Vary the exact spot between injections, and ask a pharmacist or nurse to demonstrate the first time.
Do weight-loss pens need to be kept in the fridge?
Yes — before first use, all three licensed pens are stored at 2–8 °C and must never be frozen.[1][2][3] Once in use: Saxenda can be kept for 1 month below 30 °C or in the fridge,[3] and the emc summary for Mounjaro reports up to 30 days not above 30 °C.[2] For Wegovy the exact in-use window is printed in the leaflet in your box.[1]
Can I take a Mounjaro or Wegovy pen on a plane?
Talk to your pharmacist before you fly. Keep pens in your hand luggage, in the original carton with its dispensing label, where you control the temperature — no label permits freezing,[1][2][3] and once in use the Mounjaro and Saxenda labels cap storage at around 30 °C.[2][3] Wegovy's exact in-use limit is printed in the leaflet in your box.[1] Ask about cool bags and dose timing across time zones.
What should I do if I miss a dose?
Check your own patient information leaflet — the rule depends on which pen you use and how late you are, and it differs between the weekly pens (Wegovy, Mounjaro) and once-daily Saxenda. If you are unsure, phone your pharmacy — and do not inject anything extra to catch up until the leaflet or a pharmacist has confirmed what to do.
How do I get rid of used needles in the UK?
Follow the disposal instructions in your pen's patient information leaflet, and ask the pharmacy that dispenses your pens what applies where you live — your GP surgery or local council may also be involved. Get the answer before your first injection. More everyday questions are answered on our FAQ page.
References
- electronic medicines compendium (emc). Wegovy (semaglutide 2.4 mg) FlexTouch pre-filled pen — Summary of Product Characteristics. medicines.org.uk/emc/product/13803/smpc
- electronic medicines compendium (emc). Mounjaro (tirzepatide) KwikPen — Summary of Product Characteristics. medicines.org.uk/emc/product/15481/smpc
- electronic medicines compendium (emc). Saxenda (liraglutide 6 mg/mL) pre-filled pen — Summary of Product Characteristics. medicines.org.uk/emc/product/2313/smpc
- Medicines and Healthcare products Regulatory Agency (MHRA). Single-dose 7.2mg semaglutide (Wegovy) pen approved to treat adult patients with obesity. GOV.UK, 14 April 2026. gov.uk