How Long GLP-1 Medications Stay Fresh in Your Refrigerator

GLP-1 medications last 28 days after you open them, even if the vial or pen is still half full

GLP-1 receptor agonists — the medications sold as Ozempic, Wegovy, Mounjaro, and Zepbound — have a strict expiration window once you puncture the vial or use the pen for the first time. Most manufacturers set this at 28 days, regardless of how much medication remains. After 28 days, the active ingredient begins to break down, and the medication loses potency even if it looks clear and unchanged.

This is different from food storage because pharmaceutical stability depends on chemical integrity, not just visible signs of spoilage. A vial that looks perfectly fine on day 29 may contain medication that no longer works as intended. Your body won't tell you the dose is weak — you'll simply get less effect than you paid for.

The 28-day clock starts the moment you first use the pen or vial, not the date you bought it or the date printed on the box. If you open a pen on a Tuesday and don't use it again until the following Tuesday, you have 27 days left, not 28.

Key Takeaways

• Once opened, GLP-1 pens and vials must be discarded after 28 days, even if medication remains inside.
• The 28-day countdown begins the moment you first inject or use the pen, not the purchase date.
• Unopened vials and pens last until the printed expiration date if stored in the refrigerator at 36–46°F (2–8°C).
• If a pen or vial freezes or sits at room temperature for more than 30 minutes, it should not be used even if within the 28-day window.
• Write the date you open each pen or vial directly on it with a permanent marker so you never lose track of the deadline.

Storage temperature matters as much as the 28-day rule

GLP-1 medications are sensitive to heat and cold. The safe range is 36–46°F (2–8°C) — the temperature most refrigerators maintain in the main compartment. This is narrower than the range for most foods, so a standard fridge works, but a freezer or a warm shelf does not.

If a pen or vial freezes, the medication crystallizes and becomes unusable. If it sits on a counter or in a warm car, the active ingredient degrades faster than the 28-day window allows. Even 30 minutes at room temperature can begin to damage the medication, though a single brief exposure usually won't ruin it. Repeated or prolonged exposure will.

Before each injection, hold the pen or vial in your hand for a few minutes to let it reach room temperature. Do not use it cold from the fridge — the injection will be uncomfortable and the medication may not disperse properly under the skin. After you inject, return it to the refrigerator immediately.

How to track the 28-day expiration on your pen or vial

Manufacturers do not print an "open date" on the packaging because they don't know when you'll use it. You must create your own record. The simplest method is to write the date you first use the pen or vial directly on it with a permanent marker. Write it on the label or on the plastic body where you can see it every time you reach for it.

If you use the same pen multiple times per week, mark the date in two places — on the pen itself and on your phone calendar or a paper calendar on your fridge. This redundancy prevents the mistake of losing track halfway through the month. Set a phone reminder for day 27 so you order a refill before the current pen expires.

If you share a refrigerator with others, label the pen or vial with your name as well as the date. This prevents someone else from accidentally using it or throwing it away thinking it's expired.

What happens if you use medication past 28 days

Using a GLP-1 medication after the 28-day window has closed will not cause immediate harm or a sudden reaction. The medication does not become toxic. However, the concentration of the active ingredient drops over time, so each injection delivers less of the drug than it should. You may notice weaker appetite suppression, smaller weight loss, or less stable blood sugar control.

Because the decline is gradual, you might not realize the medication is no longer working at full strength. You may assume your body has adapted to the dose, when in fact you're injecting a weakened version. This is why the 28-day limit exists — to ensure every dose you pay for is at full potency.

If you accidentally use medication past 28 days, do not panic. One injection of expired medication will not harm you. Simply note the date and plan to discard the pen or vial at the 28-day mark going forward. If you're concerned about the effectiveness of a recent injection, contact your prescriber.

Unopened pens and vials have a longer shelf life

Before you open a pen or vial, it lasts much longer — usually until the expiration date printed on the box, which is typically one to two years from the manufacturing date. This expiration date assumes the medication is stored in the refrigerator at the correct temperature and has never been opened.

Check the printed expiration date when you receive a new prescription. If it's within a few months, ask your pharmacy if they have a newer batch. If you won't use the pen or vial before the printed date, store it in the refrigerator and do not open it until you're ready to start using it.

Once you open it, the printed expiration date no longer applies. The 28-day countdown replaces it. Even if the box says the medication expires in 2025, if you open the pen in January, you must discard it by February 28 regardless of what the original label says.

Traveling with GLP-1 medications and refrigeration

If you travel and need to keep your pen or vial cold, use an insulated travel case designed for medications. These cases hold ice packs or cooling elements and maintain the 36–46°F range for several hours. Many pharmacies sell them, or you can order them online. Bring two ice packs so you can rotate them if one begins to thaw.

If you're traveling for more than a few hours and won't have access to a refrigerator, ask your prescriber whether you can skip a dose or delay it until you return home. Do not leave the medication in a hot car or exposed to direct sunlight, even briefly. If the pen or vial has been unrefrigerated for more than 30 minutes, err on the side of caution and do not use it.

When you return from travel, put the medication back in the refrigerator immediately. The 28-day countdown continues from the date you first opened it, not from when you traveled.

Signs that a GLP-1 medication should not be used

Even if the medication is within the 28-day window, discard it if any of these conditions are true: the liquid is cloudy or discolored (it should be clear), there are visible particles or crystals inside, the pen or vial has been frozen, or it has been left at room temperature for more than 30 minutes. Do not try to use it "just this once" — a compromised medication may not work, and you'll waste a dose.

If the pen or vial has been dropped or damaged, inspect it carefully. If the seal is broken or the needle is bent, do not use it. If the exterior is cracked but the seal is intact, it may still be safe, but contact your pharmacy to ask before injecting.

Frequently Asked Questions

Can I use a GLP-1 pen that's been in the fridge for 29 days?

No. The 28-day limit is firm because the medication's chemical stability degrades after that point. Even one day past the deadline means the active ingredient has begun to break down. Discard it and use a new pen or vial.

What if I forget to refrigerate my pen overnight?

If it was left out for a few hours, it's likely still safe to use. If it was left out overnight (8+ hours), do not use it. The medication may have degraded beyond safe potency. Contact your pharmacy or prescriber to ask whether you should skip that dose or use a backup pen.

Do I need to write the date on the box, or just on the pen?

Write it on the pen or vial itself, not just the box. The box may be discarded or stored elsewhere, but the pen stays with you. You need to see the date every time you reach for it.

If I use my GLP-1 pen once a week, does it last longer than 28 days?

No. The 28-day limit is calendar days, not injection days. Whether you inject once a week or three times a week, you must discard the pen 28 days after you first use it.

Can I freeze a GLP-1 pen to make it last longer?

No. Freezing damages the medication and makes it unusable. Store it only in the refrigerator at 36–46°F (2–8°C). If it has frozen, do not attempt to thaw and use it.