How long can a Wegovy pen stay out of the fridge?

Unopened pens are stored in the fridge (do not freeze). After first use, the pen can be kept below 30 °C and should be discarded 6 weeks after first use — even if some medicine remains. Keep the cap on to protect from light, and never leave pens in hot cars, direct sun, or next to heaters.

Why storage rules matter

Wegovy is a biological medicine, meaning it is made from proteins that can lose effectiveness if exposed to the wrong conditions. Keeping unopened pens in the fridge protects them until they are needed, but once a pen is in use, the rules change. Manufacturers test stability at certain temperatures and time limits, which is why the six-week window is set. Using the pen beyond this period risks the medicine being less effective, even if it still looks fine, and both NICE (TA875) and MHRA guidance emphasise that expired pens should not be used.

Understanding temperature limits

The patient leaflet and MHRA-approved information state that in-use pens can be kept at room temperature as long as it does not exceed 30 °C. This covers typical UK indoor climates but becomes more important during heatwaves or when travelling abroad. Temperatures above this can cause the active ingredient, semaglutide, to degrade. Unlike some tablets, injectables cannot be judged by sight or smell — the solution may look unchanged but still lose potency. For this reason, both the NHS and NICE warn against leaving pens in hot cars, direct sunlight, or anywhere near heaters or stoves.

Practical tips for everyday life

For most people, storing an in-use pen is simple: keep it in its original carton, in a cool cupboard or drawer, away from sunlight and household appliances that generate heat. If you are travelling, a small insulated pouch or medical cooler can give peace of mind. Many NHS weight management services suggest patients mark the date of first use on the carton or on a calendar to make the six-week countdown clear. This avoids the common mistake of forgetting when a pen was opened, which can lead to accidental use beyond the safe period. Pharmacies also advise patients not to rely on guesswork — if in doubt, the pen should be discarded.

Why six weeks is the cut-off

The six-week limit is not arbitrary. It comes from stability testing where the manufacturer assessed how long the medicine remains effective once it is exposed to warmer conditions. Regulatory authorities such as the MHRA use these data to approve storage recommendations. NICE TA875 also adopts the same product information when issuing national prescribing advice. Even if some solution remains in the pen, it must be discarded after six weeks because its full strength is no longer guaranteed. Using weaker doses risks undermining progress seen in clinical trials like STEP-1 and STEP-5, where every injection was delivered under controlled conditions.

NHS advice on safe handling

NHS weight management teams often stress that medicine safety is about both effectiveness and avoiding unnecessary worry. A pen left too long may not only lose potency but can also make it harder to understand whether treatment is working. For people making significant lifestyle changes alongside Wegovy, sticking to the storage guidance is a way of protecting their effort. The NHS also reminds people to use a sharps bin for disposal and to request replacement supplies early if a pen has expired before finishing the contents. This helps avoid interruptions in treatment, which NICE notes can affect continuity and outcomes.

Planning for warmer weather

With UK summers becoming hotter and more people travelling abroad, thinking ahead is wise. A pen left in a car on a hot day can quickly exceed 30 °C, while freezing is just as damaging. Practical solutions include carrying a cold pack, using a portable medical cooler on long journeys, or keeping the pen indoors in a stable environment. STEP trials demonstrated that maintaining consistent dosing over months is key to sustaining weight loss and health benefits. Protecting pens from heat and following expiry rules helps ensure that the treatment you are taking is equivalent to the medicine tested in those large studies.

How research underpins guidance

The storage rules may seem strict, but they are based on real evidence. Clinical trial data submitted to NICE and regulators show that semaglutide remains stable only within clearly defined temperature and time limits. Beyond this, its molecular structure begins to break down. This is why even unused solution must be thrown away after six weeks at room temperature. Guidance from both NICE and the NHS reflects this evidence, reinforcing that treatment effectiveness depends on following these practical steps as closely as possible. Patients who handle Wegovy properly are far more likely to see results consistent with those in trials such as STEP-5, which tracked benefits for up to two years.

What the evidence shows overall

The rules for storing Wegovy pens are grounded in robust evidence about how the medicine responds to light, heat, and time. Unopened pens need refrigeration, while opened ones have a safe six-week window at room temperature below 30 °C. Sticking to these limits makes sure every dose delivers the intended benefit, just as in the trials used by NICE and the NHS to guide practice. The research highlights that even small lapses — leaving a pen in direct sun or using it past six weeks — can reduce effectiveness. Following the guidance is a straightforward way to protect your treatment and keep results on track.