What Happens If You Take Semaglutide After the Expiration Date

What the stability science says about expired semaglutide

Pharmaceutical manufacturers establish expiry dates through accelerated and real-time stability testing: samples are stored under controlled conditions, analysed at intervals, and the date is set at the point where potency or purity drops below an acceptable threshold. For peptide-based medicines like semaglutide, the degradation pathways include hydrolysis (water breaking peptide bonds), oxidation of specific amino acid residues, and physical aggregation. The result is a solution that may contain less intact semaglutide and more breakdown products than when it left the factory.

The electronic Medicines Compendium (eMC), which hosts the Summary of Product Characteristics for Wegovy, specifies that the pen must be discarded after the expiry date printed on the label, and that opened pens must be used within six weeks even if the overall expiry date has not yet passed. Those two limits are independent, whichever comes first applies. If you have used semaglutide beyond either boundary, the guidance is unambiguous: do not continue with that pen.

There is no published evidence that a single expired dose causes acute harm in a healthy adult, but there is also no evidence base for assuming it is fine. Reduced potency at a critical point in your titration schedule could leave your appetite control inadequately managed that week, and in a worst case (where storage conditions were poor as well) degraded peptide fragments enter the injection site. Neither outcome is acceptable when a replacement pen is the straightforward solution. If you are ever uncertain about dosing timing, our page on what happens if you take expired semaglutide goes into further detail, and your prescriber is the right first call for personal advice.

How storage conditions interact with the expiry date

The expiry date on a Wegovy pen is calculated assuming the pen has been stored correctly throughout its shelf life: refrigerated at 2–8°C, away from direct light, and never frozen. Once those conditions are violated, the effective shelf life may shorten regardless of what the label says. A pen that spent two weeks in a gym bag in summer, or sat on a sunny windowsill, could be compromised well before its printed date.

This is where everyday routine matters. Storing your pen in the fridge door (where temperature fluctuates more than in the main body of the fridge) is less ideal than a middle shelf away from the freezer compartment. Some people travel with a pen at room temperature, which the SmPC permits for a limited window (the exact duration is stated in the Patient Information Leaflet; always check it rather than relying on a remembered figure). The point is that expiry and storage are linked: both must be satisfied, not just one.

A pen that looks fine, with a clear, colourless solution and no visible particles, can still be degraded. Peptide breakdown is molecular, nothing you can see with the naked eye will confirm whether the medicine is still potent. For practical guidance on where and how to inject, our page on the best injection sites for Wegovy covers rotation technique in detail, but equipment integrity (including the pen's condition) is the upstream step.

What to do if you realise your pen has expired

The practical steps are straightforward. Do not use the pen. Dispose of it safely using a sharps container, placing a used or expired pen in household waste creates a needlestick risk for anyone handling the bin. Contact your prescriber or pharmacy as soon as possible and explain the situation; they can advise on whether to delay that week's dose, use a new pen straight away, or take another approach depending on where you are in your titration schedule.

Missing a single weekly dose because of an expired pen is not ideal, but it is far less disruptive than injecting a compromised medicine. Timing flexibility within the weekly schedule is something your prescriber can clarify, the general advice is that one missed or delayed dose rarely derails progress, but that decision belongs with the clinician, not a general webpage.

If you are taking semaglutide as part of a privately managed programme and you run into stock or timing questions (or if concerns about dosing more broadly prompt a conversation about your treatment) what comes after a course of Wegovy is also worth understanding early, so you are not caught off guard later. At nume, every repeat order goes through clinical review before dispatch, which means your prescriber is actively checking on your progress at each stage rather than simply fulfilling a repeat.

A brief note on semaglutide sold outside a regulated supply chain

Concerns about expired semaglutide are particularly acute with pens obtained outside a regulated UK pharmacy, where cold chain integrity and genuine expiry dates cannot be verified. The MHRA has warned publicly about counterfeit and illegally traded weight-loss pens circulating online; in one enforcement operation alone, approximately 20 million doses with a street value of around £45 million were seized. A pen from an unverified seller may be counterfeit, improperly stored from the point of manufacture, or relabelled with a false date. There is no way for a patient to distinguish this from a genuine product by inspection alone.

Legitimate supply means a pen that arrives through the licensed UK supply chain, dispensed by a GPhC-registered pharmacy against a valid prescription, with cold chain maintained to your door. If you would like to understand what the private treatment landscape looks like (including how costs vary across providers) our overview of Wegovy pricing in the UK sets out the honest picture. And if you are ready to have your suitability assessed by a real prescriber rather than a form, you can check your eligibility with our clinical team.