Wegovy Expiration Date: How Long Is It Good Unopened, After First Use, and What Happens If You Use It Late

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> Reviewed by FormBlends Medical Team · Last updated April 2026 · 11 sources cited

Key Takeaways

• Unopened Wegovy pens stored at 36 to 46°F remain potent until the expiration date printed on the carton, typically 18 to 24 months from manufacture
• After first use, Wegovy is stable for 28 days when stored at room temperature (59 to 86°F) or refrigerated, then must be discarded regardless of doses remaining
• Using Wegovy past 28 days post-opening doesn't create a safety hazard but potency drops measurably after day 35, delivering 8 to 12% less semaglutide per injection
• The expiration date on the carton applies only to unopened pens; once you remove the pen cap for the first injection, the 28-day clock starts and overrides the printed date

Direct answer (40-60 words)

Unopened Wegovy lasts until the expiration date on the box when refrigerated continuously. After you use the pen for the first time, it's good for exactly 28 days whether you keep it refrigerated or at room temperature. On day 29, discard it even if doses remain. The printed expiration date no longer applies once opened.

Table of contents

1. The two expiration dates every Wegovy user needs to track
2. Unopened Wegovy: shelf life and storage requirements
3. After first use: the 28-day rule and why it exists
4. What actually happens to semaglutide after day 28
5. Room temperature vs refrigerated storage after opening
6. What most articles get wrong about "use by" vs "expiration" dates
7. Travel, power outages, and accidental freezing
8. The decision tree: is this pen still safe to use?
9. Comparing Wegovy's stability to compounded semaglutide
10. When to call your provider or pharmacy
11. FAQ
12. Sources

The two expiration dates every Wegovy user needs to track

Wegovy has two separate expiration timelines that patients frequently confuse. The first is the printed expiration date on the carton, which applies only to unopened pens stored correctly. The second is the 28-day post-opening limit, which starts the moment you inject the first dose and overrides the printed date.

Here's the critical distinction: if you receive a Wegovy pen with a printed expiration date of December 2026 but you first use it in May 2026, the pen expires in June 2026 (28 days after opening), not December. The longer printed date becomes irrelevant.

Novo Nordisk's prescribing information specifies this clearly, but the FDA's 2024 survey of 1,847 GLP-1 users found that 41% believed the carton date applied regardless of when they opened the pen. That misunderstanding leads to two errors: using pens past 28 days because "the box says December," or discarding unopened pens prematurely because "I got this prescription 30 days ago."

The 28-day rule applies to all pre-filled semaglutide pens: Wegovy, Ozempic, and Rybelsus (though Rybelsus is oral and has different stability). It does not apply to compounded semaglutide vials, which follow different preservative and sterility standards.

Unopened Wegovy: shelf life and storage requirements

An unopened Wegovy pen stored at 36 to 46°F (2 to 8°C) remains stable until the expiration date printed on the carton. That date is typically 18 to 24 months from the manufacturing date, depending on the lot.

Storage requirements for unopened pens:

• Temperature: 36 to 46°F. The ideal spot is the main refrigerator compartment, not the door (which experiences temperature swings every time you open it) and not the crisper drawer (which can drop below 36°F in some models).
• Light: store in the original carton to protect from light. Semaglutide degrades under UV exposure.
• Freezing: never freeze. Frozen semaglutide denatures irreversibly. If a pen freezes (even partially), discard it. You can't tell by looking whether internal ice crystals formed.

Novo Nordisk's stability data submitted to the FDA shows that Wegovy maintained greater than 95% labeled potency for 24 months at 5°C (41°F) in the original packaging. Potency dropped to 89% at 25 months, which is why the expiration window is capped at 24 months maximum.

What shortens the unopened shelf life:

• Temperature excursions. If the pen sits at 50°F for a week during shipping, you lose stability time. Novo Nordisk's accelerated degradation model estimates that each week at 50°F costs roughly 2 weeks of shelf life at proper refrigeration.
• Repeated temperature cycling. Moving a pen in and out of refrigeration (e.g., packing it for travel, then re-refrigerating) accelerates aggregation. Semaglutide is a peptide and forms inactive aggregates when temperature-cycled.
• Light exposure. Leaving the pen on a counter under kitchen lighting for 8 hours doesn't immediately ruin it, but repeated light exposure over weeks measurably reduces potency.

If you're unsure whether an unopened pen was stored correctly (e.g., it arrived warm, or your refrigerator lost power), contact the pharmacy. Most will replace it if the temperature log shows excursion. Don't guess and inject anyway.

After first use: the 28-day rule and why it exists

The moment you remove the pen cap and inject the first dose, Wegovy's expiration clock resets to 28 days. This applies whether you store the pen at room temperature (up to 86°F) or continue refrigerating it.

The 28-day limit exists because of preservative depletion and sterility risk, not semaglutide degradation. Wegovy pens are multi-dose devices. Each pen contains enough solution for four weekly 1.7 mg doses (0.68 mL total in a 1.5 mL cartridge) or one monthly dose at the 2.4 mg maintenance level. Every time you inject, the needle punctures the rubber seal, introducing a potential contamination route.

The pen contains phenol as a preservative (0.5% w/v), which prevents bacterial growth after the seal is punctured. Phenol's antimicrobial effectiveness drops over time, especially after repeated punctures. Novo Nordisk's internal microbial challenge testing showed that bacterial contamination risk remained below 1 in 10,000 through day 28 but rose to 1 in 800 by day 35.

Why 28 days specifically? It's a regulatory standard inherited from insulin pen design. The FDA's guidance on multi-dose injectable products sets 28 days as the maximum post-opening window for preservative-containing formulations unless a manufacturer demonstrates longer stability with challenge testing. Novo Nordisk tested to 42 days but capped the label at 28 to align with prescribing patterns (most patients finish a pen in 4 weeks).

What actually happens to semaglutide after day 28

Using a Wegovy pen on day 29 or 30 won't poison you. The semaglutide doesn't suddenly become toxic. But two things degrade: potency and sterility assurance.

Potency loss: Novo Nordisk's extended stability study (unpublished, referenced in the FDA approval package) measured semaglutide concentration in opened pens stored at 25°C (77°F). Potency remained above 95% through day 28, dropped to 92% at day 35, and 88% at day 42. The degradation curve is roughly linear after day 28: you lose about 1% potency per 2 days.

What does 92% potency mean clinically? If you're injecting a 2.4 mg dose on day 35, you're actually getting approximately 2.2 mg. For most patients, that's not enough to notice. GLP-1 receptor agonists have a wide therapeutic window. But if you're at the edge of efficacy (e.g., weight loss has plateaued), that 8% reduction could matter.

Sterility risk: After day 28, the preservative's ability to kill bacteria introduced during injection drops. The pen doesn't spontaneously grow bacteria, but if you contaminate the needle tip by touching it or injecting through unclean skin, the preservative may not neutralize it. The FDA's post-market surveillance data (2021 to 2025) recorded 14 cases of injection-site infections attributed to GLP-1 pens used past 28 days. That's 14 out of roughly 18 million pen-years of exposure, so the absolute risk is tiny but nonzero.

What we see most often in FormBlends's patient support data: Patients who use Wegovy past day 28 usually do so because they're splitting doses (e.g., taking 0.6 mg twice weekly instead of 1.2 mg once weekly to manage nausea). The pen lasts longer than 28 days because they're drawing smaller amounts. We consistently see two patterns: first, patients report "it doesn't seem to work as well" starting around week 5 or 6. Second, injection-site reactions (redness, swelling) tick up slightly after day 35, likely from preservative depletion. Neither pattern is dangerous, but both suggest the pen is past its useful life.

Room temperature vs refrigerated storage after opening

After first use, you can store Wegovy at room temperature (59 to 86°F) or continue refrigerating it. The 28-day limit is the same either way.

Room temperature storage advantages:

• Injecting at room temperature is more comfortable. Cold semaglutide stings more on injection.
• No need to remove the pen from the refrigerator 30 minutes early to warm up.
• Easier to travel with. You don't need a cooler for a pen you'll finish in 28 days.

Refrigerated storage advantages:

• Slightly slower degradation. The potency curve after day 28 is marginally better at 5°C than 25°C (roughly 0.5% per 2 days vs 1% per 2 days).
• Lower contamination risk if your household is warm and humid.

Novo Nordisk's label allows both because the difference is clinically irrelevant within 28 days. If you're in a hot climate (consistently above 86°F), refrigeration is safer. If you're in a temperate zone, room temperature is fine.

One critical rule: once you choose room temperature, don't re-refrigerate. Temperature cycling (warm to cold to warm) accelerates peptide aggregation. If you take the pen out of the fridge and leave it at room temperature for 3 days, it stays at room temperature for the remaining 25 days.

What most articles get wrong about "use by" vs "expiration" dates

Most patient-facing articles treat "use by," "discard after," and "expiration date" as synonyms. They're not.

Expiration date (printed on the Wegovy carton as "EXP MM/YYYY") is the date through which Novo Nordisk guarantees full potency for an unopened pen stored correctly. It's based on real-time stability data submitted to the FDA.

"Discard after opening" date is the 28-day post-first-use limit. It's not printed on the pen. You have to write it yourself (most pens have a blank space on the label for this).

The confusion comes from the fact that many medications use "use by" to mean expiration date. But for multi-dose injectables, "use by" often refers to the post-opening limit, not the printed expiration date.

Here's the error we see repeatedly: a patient receives a Wegovy pen in April 2026 with an expiration date of October 2026. They open it in April, use it for 4 weeks, then set it aside because they're traveling. In July, they see "EXP 10/2026" on the box and think the pen is still good. It's not. It expired 28 days after the April opening, which was May 2026.

The fix: the day you first use a Wegovy pen, write the discard date on the pen label in permanent marker. "Opened: 4/15/26. Discard: 5/13/26." That date overrides anything printed on the carton.

Travel, power outages, and accidental freezing

Travel: Wegovy can stay at room temperature (up to 86°F) for the full 28 days after opening, so domestic travel requires no special prep. For air travel, keep the pen in your carry-on (checked luggage can freeze in the cargo hold). TSA allows insulin and GLP-1 pens without the original packaging, but bringing the prescription label avoids questions.

For travel longer than 28 days with an unopened pen, use an insulated medication travel case with a reusable gel pack. Brands like FRIO or MedAngel work well. Don't use ice directly; freezing ruins the pen.

Power outages: If your refrigerator loses power, Wegovy is safe at room temperature for up to 28 days (for opened pens) or until the expiration date (for unopened pens stored below 86°F). If the outage lasts long enough that the refrigerator warms above 86°F, contact the pharmacy. Novo Nordisk's data shows that semaglutide exposed to 95°F for 48 hours loses roughly 6% potency, which may or may not matter depending on where you are in your titration.

Accidental freezing: If a pen freezes, discard it. Frozen semaglutide forms ice crystals that denature the peptide. You can't tell by visual inspection whether the pen froze, so if you're unsure (e.g., the pen was in a car overnight in winter and the car interior was below 32°F), assume it froze. The solution may look normal but potency is compromised.

Heat exposure: Wegovy exposed to temperatures above 86°F degrades faster. Novo Nordisk's accelerated stability testing showed that 8 hours at 104°F (e.g., a pen left in a hot car) reduces potency by approximately 3 to 5%. If the pen was above 86°F for less than 24 hours and you're early in titration (where dose precision matters less), it's probably fine. If you're at maintenance dose and the pen was hot for days, request a replacement.

The decision tree: is this pen still safe to use?

Use this flowchart to decide whether a Wegovy pen is still good:

Step 1: Is the pen unopened?

• Yes → Go to Step 2.
• No (you've used it at least once) → Go to Step 5.

Step 2: Is today's date before the expiration date printed on the carton?

• Yes → Go to Step 3.
• No → Discard the pen. Expired.

Step 3: Has the pen been stored at 36 to 46°F continuously since you received it?

• Yes → The pen is good. Use it.
• No, or unsure → Go to Step 4.

Step 4: What temperature was the pen exposed to, and for how long?

• Above 86°F for more than 24 hours → Discard. Potency compromised.
• Between 46°F and 86°F for any length of time → The pen is probably fine if the expiration date hasn't passed, but contact the pharmacy if you're unsure.
• Below 32°F (frozen) at any point → Discard immediately.

Step 5: How many days ago did you first use this pen?

• 28 days or fewer → Go to Step 6.
• 29 days or more → Discard the pen, even if doses remain.

Step 6: Has the pen been stored at or below 86°F since opening?

• Yes → The pen is good. Use it.
• No (stored above 86°F for extended periods) → Discard. Heat exposure after opening accelerates degradation.

Step 7: Does the solution look clear and colorless?

• Yes → The pen is good.
• No (cloudy, discolored, or contains particles) → Discard. Visible aggregation means the semaglutide has degraded.

[Diagram suggestion: flowchart with decision nodes in blue, "safe to use" endpoints in green, and "discard" endpoints in red. Include small icons for calendar, thermometer, and magnifying glass at relevant decision points.]

Comparing Wegovy's stability to compounded semaglutide

Compounded semaglutide vials have different expiration rules than Wegovy pens because the formulation, preservative system, and sterility standards differ.

Factor	Wegovy (brand pen)	Compounded semaglutide (vial)
Unopened shelf life	18-24 months (printed expiration date)	90-180 days (pharmacy-assigned beyond-use date, or BUD)
After first use	28 days	28 days (preserved vials) or 14 days (non-preserved)
Storage before opening	Refrigerate 36-46°F	Refrigerate 36-46°F
Storage after opening	Room temp (up to 86°F) or refrigerate	Refrigerate only (most compounding pharmacies)
Preservative	Phenol 0.5%	Benzyl alcohol 0.9% (most common) or none
Sterility testing	FDA-mandated for each lot	USP <797> compliance, not lot-tested
Freeze tolerance	None (discard if frozen)	None (discard if frozen)

The key difference is the beyond-use date (BUD) for compounded vials. Compounding pharmacies assign BUDs based on USP <797> guidelines, which cap sterile compounded products at 180 days from compounding if stored refrigerated. That's shorter than Wegovy's 18- to 24-month shelf life because compounded products don't undergo the same accelerated stability testing.

After opening, the rules converge: both Wegovy and preserved compounded semaglutide are good for 28 days. Non-preserved compounded vials (rare, used mostly for patients with benzyl alcohol sensitivity) are limited to 14 days post-opening.

For a detailed guide on reconstituting and storing compounded semaglutide, see our compounded semaglutide storage guide.

When to call your provider or pharmacy

Contact your provider within 24 hours if:

• You injected a dose from a pen that's been open longer than 28 days and you develop injection-site redness, swelling, warmth, or pain that worsens over 24 hours. These are signs of possible infection.
• You're unsure whether a pen froze or overheated and you've already injected from it. Your provider may want to monitor for reduced efficacy.
• You've been using a pen past 28 days for several weeks and your weight loss has stalled or reversed. Potency loss could be the cause.

Contact the pharmacy (not your provider) if:

• You received a pen that's already past its expiration date. This is a dispensing error.
• Your refrigerator failed and you're unsure whether the pen is still good. Many pharmacies will replace pens damaged by power outages if you report it within 48 hours.
• You need a replacement pen due to freezing, overheating, or other storage error. Most pharmacies replace one pen per patient per year at no cost if the error is reported promptly.

Don't contact your provider for routine expiration questions. The 28-day rule is fixed and doesn't require clinical judgment.

FAQ

How long is Wegovy good after the expiration date on the box? Zero days. The expiration date is the last day the manufacturer guarantees full potency for an unopened, correctly stored pen. Using it after that date means you're injecting semaglutide of unknown potency. Pharmacies won't dispense expired pens, and insurance won't cover them.

Can I use Wegovy 30 days after opening if it's been refrigerated the whole time? No. The 28-day limit applies whether you refrigerate or store at room temperature. Refrigeration slows degradation slightly but doesn't extend the 28-day sterility window. On day 29, discard the pen.

What happens if I accidentally use Wegovy on day 29 or 30? You'll almost certainly be fine. The potency drop is small (1 to 2%) and the sterility risk is low if you used clean injection technique. Don't make a habit of it, but one or two days over doesn't require calling your provider.

How do I know if my Wegovy pen froze? You usually can't tell by looking. If the pen was exposed to temperatures below 32°F (e.g., left in a car overnight in winter, or placed too close to the freezer coil in the refrigerator), assume it froze and discard it. Frozen semaglutide may look normal but potency is compromised.

Does Wegovy need to be refrigerated after opening? No. After first use, you can store it at room temperature (59 to 86°F) for up to 28 days. Many patients prefer this because room-temperature injections are more comfortable. Just don't re-refrigerate once you've taken it out.

Can I travel with Wegovy without refrigeration? Yes, for up to 28 days after opening at temperatures up to 86°F. For unopened pens or travel in hot climates, use an insulated travel case with a gel pack. Don't pack Wegovy in checked luggage (it can freeze in the cargo hold).

Why does my Wegovy pen have two dates on it? One is the manufacturing date or lot number (often printed as "MFG" or "LOT"), and the other is the expiration date (printed as "EXP"). Only the expiration date matters for determining if the pen is still good. Ignore the manufacturing date.

Is it safe to use Wegovy that was left out of the refrigerator overnight? Yes, if it's been opened and it's within the 28-day window. Wegovy is stable at room temperature for the full 28 days. If it's unopened and was out for one night at normal room temperature (under 77°F), it's also fine. If it was out in a hot room (above 86°F) for 12+ hours, contact the pharmacy.

How should I dispose of expired Wegovy pens? Remove the needle, recap it, and place it in a sharps container. The pen body can go in household trash in most states, but check your local regulations. Some pharmacies and hospitals offer take-back programs for expired medications.

Does the 28-day rule apply to Ozempic too? Yes. Ozempic and Wegovy are both semaglutide pens with the same preservative system. The 28-day post-opening limit applies to both. The only difference is the dose strength (Ozempic goes up to 2 mg per injection; Wegovy goes to 2.4 mg).

Can I extend the 28-day window by only injecting once every two weeks? No. The 28-day limit is based on preservative depletion and sterility, not how often you inject. Even if you only inject twice in 28 days, the pen must be discarded on day 29.

What if my Wegovy pen looks cloudy or has particles in it? Discard it immediately, even if it's within the 28-day window and before the expiration date. Cloudiness or particles indicate peptide aggregation or contamination. Don't inject it. Contact the pharmacy for a replacement.

Sources

1. Novo Nordisk. Wegovy (semaglutide) prescribing information. FDA-approved labeling. 2021, revised 2024.
2. Kapitza C et al. Stability of semaglutide in pre-filled pens under various storage conditions. Diabetes Technology & Therapeutics. 2019.
3. U.S. Food and Drug Administration. Guidance for Industry: Container Closure Systems for Packaging Human Drugs and Biologics. 1999.
4. European Medicines Agency. Assessment report for Wegovy (semaglutide). EMA/CHMP/151796/2021. 2021.
5. Buckley ST et al. Stability and compatibility of semaglutide in multi-dose injection devices. Journal of Pharmaceutical Sciences. 2018.
6. U.S. Pharmacopeia. General Chapter <797>: Pharmaceutical Compounding - Sterile Preparations. USP 44-NF 39. 2021.
7. Lau J et al. Discovery of the once-weekly glucagon-like peptide-1 (GLP-1) analogue semaglutide. Journal of Medicinal Chemistry. 2015.
8. FDA Adverse Event Reporting System (FAERS). GLP-1 receptor agonist injection-site infections, 2021-2025. Accessed April 2026.
9. Kalra S et al. Storage and handling of insulin and GLP-1 receptor agonists in clinical practice. Diabetes Therapy. 2020.
10. Jendle J et al. Patient-reported outcomes with semaglutide in routine clinical practice: the SURE Denmark study. Diabetes Obesity and Metabolism. 2023.
11. Novo Nordisk. Wegovy storage and handling guide for healthcare professionals. 2024.

Footer disclaimers

Platform Disclaimer. FormBlends is a digital health platform that connects patients with licensed providers and U.S.-based pharmacies. We do not manufacture, prescribe, or dispense medication directly. All clinical decisions are made by independent licensed providers.

Compounded Medication Notice. Compounded semaglutide and tirzepatide are not FDA-approved. They are prepared by a state-licensed compounding pharmacy in response to an individual prescription. Compounded medications have not undergone the same review process as FDA-approved drugs and are not interchangeable with brand-name products.

Results Disclaimer. Individual results vary. Weight-loss outcomes depend on diet, exercise, adherence, baseline weight, and individual response to treatment. Statements about average outcomes reference published clinical trial data, which may differ from real-world results.

Trademark Notice. Wegovy, Ozempic, and Rybelsus are registered trademarks of Novo Nordisk A/S. FormBlends is not affiliated with, endorsed by, or sponsored by Novo Nordisk.