FDA approves 21 days of in-use storage with temperature cycling for Mounjaro and Zepbound

On April 22, 2026, the Food and Drug Administration approved labeling changes for Mounjaro and Zepbound that allow single-dose tirzepatide vials and semi-finished syringes to spend up to 21 days in and out of refrigeration during patient use, including repeated moves between the refrigerator and room temperature ^[1].

The two approvals came as prior-approval supplemental new drug applications: NDA 215866/S-052 for Mounjaro (tirzepatide) injection, solution, and NDA 217806/S-050 for Zepbound (tirzepatide) injection, solution. Both were submitted on March 9, 2026, and received by the agency the same day, according to the approval letter addressed to Eli Lilly's regulatory affairs office ^[1]. The letter states that both supplements are approved effective on its date, April 22, 2026 ^[1].

The agency describes the supplements as covering a "stability patient-use study" showing the drug product "maintains acceptable quality when stored in and out of refrigeration during patient use period for up to 21 days, including multiple transitions between refrigerated and room-temperature condition" ^[1].

The letter quotes Lilly's conclusion from that study. Test results at the start of the cycling phase and at the 21-day timepoint showed "no practical difference between control versus cycled samples against the acceptance criteria," the company told the agency. Cycling between 5 °C (about 41 °F) and 30 °C (about 86 °F) "had no impact on the drug product critical quality attributes," and cumulative storage with that temperature cycling "is supported for the 21-day in-use period" for single-dose (vials and semi-finished syringes) tirzepatide presentations ^[1].

Several boundaries are not settled in the letter. The quoted conclusion names single-dose vials and semi-finished syringes; the letter's enclosure list also includes instructions for use for the vial and for the single-dose pen ^[1]. The letter does not say whether multi-dose pens or other presentations are covered by the change, does not state what the previous in-use storage limit was, and does not address storage above 30 °C or beyond the tested 21-day period ^[1]. It also says nothing about price, insurance coverage or supply.

Why it matters for patients

For people using the single-dose presentations named in the letter, the label can now reflect a 21-day in-use window during which the medicine may move between the refrigerator and room temperature more than once ^[1]. That matters for travel, for days when a refrigerator is unavailable, and for households that take a dose out and then put it back.

The 21 days are cumulative, not per-trip: the study covered the in-use period as a whole, with repeated transitions inside it ^[1]. The tested room-temperature limit was 30 °C, about 86 °F, and the letter does not describe what happens above that ^[1].

The supplements concern storage of the drug product. The letter describes no change to strengths or dosing, and it does not address product that has already been stored outside the tested conditions ^[1].

What happens next

The letter sets dates for the company, starting from April 22, 2026:

• Within 14 days, Lilly must submit the content of labeling in structured product labeling format, identical to the labeling the FDA enclosed ^[1].
• Also within 14 days, the company must amend pending supplemental applications that include labeling changes for this application, providing both an annotated and a clean version ^[1].
• Within 30 days of approval, Lilly must submit required patent information on Form FDA 3542 for listing in the Orange Book ^[1].
• Final printed carton and container labels must be submitted as soon as they are available, but no more than 30 days after they are printed ^[1].

FDA approval is not required before the labels are used, the letter states ^[1]. Whether the updated prescribing information and Medication Guide have been posted has not been disclosed in the letter ^[1].