A GLP-1 lives in the refrigerator, and that is the part everyone remembers. The number that decides whether a dose is still good is the other one: how long the product is allowed to be out of a refrigerator. That figure is not the same for any two of the four approved injectables, and it is not a property of the molecule.
The cold range is the one thing they agree on
Wegovy, Ozempic, Zepbound and Mounjaro all specify refrigerated storage at 2°C to 8°C (36°F to 46°F).[1][2][3][4] All four instruct against freezing and against using a product that has been frozen. Novo Nordisk adds that the product should not be stored directly adjacent to the cooling element, which is the coldest spot in a domestic refrigerator.
Light is handled the same way by both manufacturers. Wegovy is to be protected from light and kept in its original carton until the time of administration; Zepbound and Mounjaro are to be protected from heat and light and stored in the original carton for that purpose. The carton is part of the instruction rather than packaging to be thrown away, which is easy to miss when a dose is being carried in a bag. If you are still choosing between molecules, the trial comparison is a separate question from this one.
The room-temperature allowance is where they split
A Wegovy single-dose pen or syringe may be kept from 8°C to 30°C (46°F to 86°F) for up to 28 days, and the label attaches that allowance to the period before the cap is removed.[1] An Ozempic single-dose prefilled syringe carries the same 28 days across the same range.[2]
Lilly’s single-dose presentations are shorter. A Zepbound or Mounjaro single-dose pen or single-dose vial may be stored unrefrigerated at temperatures not exceeding 30°C (86°F) for up to a total of 21 days, and the label then says to discard it.[3][4]
Twenty-eight days and twenty-one days are not interchangeable. Neither number describes semaglutide or tirzepatide as substances; each describes one manufacturer’s formulation inside one container. A summary that rounds both to “about a month” gives a week of false headroom to half the category.
Opening a multi-dose device starts a second clock
Devices holding several doses are dated differently. An Ozempic pen may be stored for 56 days after first use, at 15°C to 30°C (59°F to 86°F) or refrigerated.[2] The Wegovy FlexTouch single-patient-use pen, which holds four weekly 2.4 mg doses, carries the same 56 days after first use.[1]
Lilly’s multi-dose presentations run to a different number and hold three conditions at once. An unopened multi-dose vial or KwikPen kept at room temperature is discarded after 30 days. Once opened, the label instructs discarding it after a total of 30 days at room temperature, 30 days after first use, or after four weekly doses, even if medicine remains in it.[3][4]
That clause repays a second reading, because it is the only place in this category where an FDA-reviewed label dates a multi-dose vial. It is also the closest published analog to what most sellers here actually ship — see the compounded semaglutide board for who those sellers are.
Why the limits are counted in days
These are peptides, and peptides degrade by routes that heat speeds up. A preformulation study stressed semaglutide in solution at 25°C, 40°C, 60°C and 80°C and identified thirteen known degradation impurities, six of which appeared under every condition tested. The extent of degradation tracked temperature, pH and the buffer the peptide was sitting in.[5]
That is a laboratory stress experiment, not a simulation of a warm car, and it does not say how much potency any pen loses on a countertop. What it establishes is the shape of the problem. The allowances above are finite for a reason, and the reason is chemistry rather than caution.
Travel turns the label into arithmetic
None of the four labels addresses air travel as such. What they supply is the range a cooler has to hold, and the budget it is spending. A pen carried at room temperature for a weekend has used part of its 21 or 28 days. The clock does not reset on return to a refrigerator.
The freezing instruction cuts the other way. A pen packed flush against a frozen gel pack can fall below 2°C, and every one of these labels says a product that has been frozen is not to be used. Nothing about a pen reveals that it happened. A pharmacist can answer an excursion question against the specific product; a website cannot.
What changes when a compounded vial replaces a pen
Every figure above belongs to an approved product with an FDA-reviewed label. A compounded multi-dose vial arrives with a date assigned by the pharmacy that made it, and that date is set under a different rulebook. Under USP General Chapter 797, a beyond-use date is the date, or the hour and date, after which a compounded sterile preparation must not be used. Its length depends on how the preparation was made rather than on what is in it.[6]
The available windows are much shorter than a manufacturer expiration date. A Category 2 preparation compounded aseptically from sterile starting components, without passing a sterility test, carries four days at controlled room temperature and ten days refrigerated. Longer dating exists, but only for a pharmacy meeting the additional Category 3 requirements, which include stability-indicating testing and sterility and endotoxin release testing. Separately, a multiple-dose preparation that has been punctured must not be used past its assigned beyond-use date or 28 days, whichever is shorter.[6]
None of that reveals how any particular vial in the mail was dated, and that is the gap worth naming. A seller shipping a month of doses in one vial is shipping a container whose dating rule it has usually not published, alongside contents it has usually not published either. Whether a pharmacy is named at all is one of the things the seller reviews record, on criteria set out in the methodology.
Storage is the quietest way a course of treatment goes wrong, because a degraded dose looks exactly like a working one. Anything about a specific vial, a specific excursion or a specific date belongs to the pharmacist who dispensed it and the prescriber who wrote it.