Key takeaways
- Unopened pens are kept in the fridge at 2-8°C. Do not freeze them, and do not store them against the cooling element.
- Once in use, a Mounjaro KwikPen can be kept below 30°C for up to 30 days; a Wegovy pen for up to 6 weeks.
- Rotate injection sites — stomach, thigh or upper arm — and never store a pen with the needle attached.
- Used needles go in a sharps bin, not household waste. Your pharmacy or council can advise on disposal.
None of this is glamorous, and all of it is the sort of thing people work out too late — usually on a Friday, in an airport, with a pen that has been in a hot car.
This page summarises what the patient information leaflets say. Your own leaflet, supplied with your medicine, is the authority for your specific product.
Before first use
Unopened pens live in the fridge at 2–8°C [1][3].
Two details matter. Do not freeze them — a frozen pen must be discarded, and the back of a fridge or the shelf against the cooling element is where freezing happens. And keep them in the outer carton, away from light.
After first use
This is where the two products differ, and it is worth knowing which you have.
| Product | After first use |
|---|---|
| Mounjaro KwikPen | Up to 30 days below 30°C, then discard [3] |
| Wegovy pen | Up to 6 weeks below 30°C or in the fridge [1] |
Two rules apply to both. Discard at the end of that window even if medicine remains — the in-use shelf life is not a suggestion. And never store a pen with the needle attached: it lets medicine leak out, air in, and contamination through.
“Below 30°C” is generous in a British winter and optimistic in a heatwave. A car in summer sun, a windowsill, or a bag on a beach will all exceed it.
Injecting
The leaflets list three areas [1]:
- The stomach, at least 5 cm away from the navel
- The upper legs (thighs)
- The upper arms
Rotate. Use a different spot each time rather than the same patch week after week, which can cause lumpy or thickened tissue that also absorbs less reliably. Where a higher dose requires more than one injection, the leaflet advises spacing them at least 5 cm apart within the same area.
Attach a new needle for every injection, and remove it immediately afterwards.
Sharps disposal
Used needles do not go in household waste, and not in a bottle or a tin either. They go in a proper sharps bin [4].
Where you get one and how it is collected varies: some pharmacies supply bins and take them back, some councils run a collection service, and some GP practices will accept them. The pharmacy that supplied your medicine is the right first question.
Travelling
Keep medicine in hand luggage. The hold is too cold, and bags get lost. This is the single most important rule.
Carry documentation. A copy of your prescription, or a letter from your prescriber naming the medicine and confirming you need needles, makes security straightforward. Keep everything in its original labelled packaging — the pharmacy label is what identifies it as yours.
Security will be fine. Injectable medicines and needles are permitted in hand luggage with supporting documentation [5]. Declare them rather than hoping they go unnoticed.
Cool bags for longer journeys. A small insulated bag with a gel pack — not in direct contact with the pen, which risks freezing — covers most flights. Specialist medication cool wallets are widely available.
Check the destination. Some countries have rules about bringing in prescription medicines. Check before you go rather than at the border.
Time zones. A weekly injection has some flexibility; the tirzepatide SmPC allows the day to be changed provided at least three days separate two doses [2]. For daily medicines, keep to a consistent local time rather than recalculating.
When something goes wrong
A pen left out too long, or frozen — do not use it. Speak to your pharmacy about a replacement.
A missed dose — follow the instruction in your leaflet rather than guessing. For tirzepatide, a missed dose can be taken within four days; after that it is skipped and the next taken on the normal day [2].
A damaged pen, or one that does not work properly — do not try to fix it or transfer the medicine. Keep it, note the batch number, and contact your pharmacy. Suspected defects and side effects can be reported through the Yellow Card scheme [6].
Frequently asked questions
Does Mounjaro have to be kept in the fridge?
Unopened pens are stored in a fridge at 2-8°C and must not be frozen. Once in use, a KwikPen can be kept unrefrigerated at up to 30°C for up to 30 days, after which it should be discarded even if medicine remains.
How long can Wegovy stay out of the fridge?
According to the patient information leaflet, after first use a Wegovy pen can be kept for up to 6 weeks either below 30°C or in a fridge at 2-8°C.
Where do you inject?
The leaflets list the stomach (at least 5 cm from the navel), the upper legs and the upper arms. Rotate sites rather than using the same spot each time. Where three injections are needed for a single higher dose, they should be spaced at least 5 cm apart.
Can you take weight loss pens on a plane?
Yes, in hand luggage — the hold gets too cold and bags go missing. Carry a copy of your prescription or a letter from your prescriber, keep the medicine in its original labelled packaging, and use a cool bag with a gel pack for longer journeys.
What do you do with used needles?
They go into a sharps bin, never into household rubbish. Ask the pharmacy that supplied your medicine or your local council about obtaining a bin and arranging collection.
References
- Novo Nordisk Limited. Wegovy: Patient Information Leaflet. Electronic Medicines Compendium. www.medicines.org.uk/emc/files/pil.13800.pdf
- Eli Lilly and Company Limited. Mounjaro KwikPen: Summary of Product Characteristics. Electronic Medicines Compendium. www.medicines.org.uk/emc/product/15484/smpc
- Eli Lilly. How should the Mounjaro (tirzepatide) KwikPen be stored? medical.lilly.com/uk/products/answers/how-should-the-mounjaro-tirzepat
- NHS. How should I dispose of used needles or sharps? www.nhs.uk/common-health-questions/medicines/how-should-i-dispose-of-u
- Civil Aviation Authority. Medication and medical equipment when flying. www.caa.co.uk/passengers/before-you-fly/am-i-fit-to-fly/guidance-for-h
- MHRA. Yellow Card: report a suspected side effect. yellowcard.mhra.gov.uk/
Medical reviewer
Naeem Teni
Clinical Lead at Manova. Registered pharmacist and independent prescriber, GPhC 2215591. Reviews Manova’s clinical content for accuracy and safety.
Written by
Manova Editorial Team
Researched and written to our editorial policy, using NICE, NHS, MHRA and peer-reviewed sources.
This article is for general information and isn’t a substitute for advice from your own clinician. If you feel unwell, contact your GP or NHS 111. In an emergency, call 999.