Semaglutide shelf life unopened: the facts, not the myths

The myth: expiry dates are just a legal formality

A common assumption is that pharmaceutical expiry dates are overly cautious, that a pen a week past its date is probably fine. For some medicines that may be true, but injectable biologics like semaglutide are a different matter. The molecule is a large peptide; its three-dimensional structure is what makes it pharmacologically active, and that structure degrades. Exposure to the wrong temperature, repeated freeze-thaw cycles, or excessive light can accelerate that degradation well before the printed date.

The expiry date on an unopened Wegovy pen is the manufacturer's guarantee that the medicine meets its licensed potency and safety specification, assuming it has been stored as directed. It is not a conservative buffer. Use a pen beyond its expiry date and you cannot know whether you are receiving the stated dose. This matters clinically: underdosing on a titrated medicine like semaglutide is not just ineffective, it can create confusion about how your treatment is progressing.

The NHS semaglutide patient information page is clear that medicines should not be used after the expiry date printed on the label. When in doubt, the Patient Information Leaflet inside every carton gives the authoritative storage instructions for that specific batch.

What actually happens during refrigerated storage

Refrigeration at 2–8°C slows the chemical processes that break peptide bonds and alter the semaglutide molecule's shape. An unopened pen kept consistently in this range will remain within specification to its expiry date. That is the core fact about Wegovy shelf life unopened: keep it cold, keep it dark, keep it in the original packaging.

Two practical risks disrupt this. First, the fridge door. Temperature fluctuations near a fridge door can be significant, particularly in a busy household. Storing your pen towards the back of a shelf, away from the door, is sensible. Second, freezing. If a semaglutide pen freezes (accidentally pushed to the back of the fridge and into a freezer zone, or stored in a freezer by mistake) it is no longer suitable for use, regardless of the expiry date. Freezing damages the formulation irreversibly.

Light exposure also matters for some biologics. Keeping the pen in its original carton until you use it is the simplest protection. If you are thinking about how storage interacts with ongoing treatment, it is worth reading about Wegovy shelf life more broadly, which covers the full picture across different storage situations.

When the shelf life calculation changes: the transition from unopened to in-use

The shelf life rules covered here apply specifically to pens that have never been used. The moment a pen is activated for its first injection, the relevant window changes, and it is shorter than most people expect. This catches patients off guard, particularly those who are not yet on the maintenance dose and use only one injection per pen per four-week period.

Understanding the distinction matters for practical planning. You can read about how Wegovy shelf life changes after opening in detail separately, but the headline is: consult the Patient Information Leaflet for the exact in-use period, because it is different from the unopened expiry. Always follow the PIL or your prescriber's guidance on this.

If you are managing a supply of pens (perhaps because you have stocked up ahead of a holiday) rotate them by expiry date and check each carton individually. Batch expiry dates can vary, and it is worth understanding how the shelf life of semaglutide changes once a pen has been opened, since that window is quite different from the unopened expiry. The half-life of semaglutide in the body is a separate question from the physical shelf life of the pen, though both matter to understanding how the medicine behaves over time.

Suspect your pen has been stored incorrectly? Here is what to do

If you have any reason to think a pen has been frozen, left in a hot car, or kept at room temperature for longer than the PIL allows, do not use it. The medicine may look identical (semaglutide is a clear, colourless liquid with no visible sign of degradation) but appearance alone cannot confirm potency.

Contact your prescriber or pharmacist. At nume, our prescriber team is available seven days a week for exactly this kind of aftercare question; you can reach us via our contact page. For a broader look at what questions our team fields most often, our FAQs cover common practical queries, including whether Wegovy can cause ovarian cysts, which is something patients on hormonal contraception often ask about.

Dispose of expired or compromised pens using a sharps container if the needle has been used, or via your local pharmacy's medicine return scheme for unused pens. Never put pens in household waste. The MHRA Yellow Card scheme allows patients to report suspected quality issues with medicines, including pens that appear compromised, a genuinely useful route if you believe something is wrong with your supply.

If you are weighing up whether semaglutide is the right treatment for your situation, it is also sensible to read about whether Wegovy is a lifelong commitment before starting, and you can check your eligibility through our free consultation, a prescriber reviews every application the same day it arrives.