Does tirzepatide expire? When?
Brand tirzepatide pens expire per the printed date (typically 18-24 months from manufacture). Once opened, use within 30 days at room temp or 90 days refrigerated.
Updated May 20, 2026 · 4 min read
Yes, tirzepatide expires. For brand-name Mounjaro and Zepbound pens, the expiration date is printed on the pen label — typically 18–24 months from the date of manufacture. Once you take a pen out of the refrigerator and start using it, the in-use window is 30 days at room temperature or up to 90 days if you keep it refrigerated.
Manufacturer Expiration vs. In-Use Expiration
These are two different clocks, and both matter.
Manufacturer expiration date (printed on the pen): This applies to the sealed, unopened pen stored correctly in the refrigerator (36–46°F / 2–8°C). It's Lilly's tested stability endpoint — the date through which the drug is guaranteed to meet potency and purity specifications. Using the drug before this date under proper storage conditions is fine. Using it after this date means the degradation timeline is unknown.
In-use stability (once you start using the pen): Once you take the pen out of the fridge and use it for the first time, the stability window shortens. Per Lilly's labeling for both Mounjaro and Zepbound:
| Condition | Max time after first use |
|---|---|
| Room temperature (up to 86°F / 30°C) | 30 days |
| Refrigerated (36–46°F / 2–8°C) | Up to 90 days |
The pen also cannot be frozen at any point. Freezing denatures peptides and renders the drug ineffective. If your pen was accidentally left in a freezer, discard it.
Compounded Tirzepatide: Different Rules
Compounded tirzepatide comes in two forms, each with different stability:
Lyophilized (freeze-dried) powder vials: The dry powder form, which requires reconstitution with bacteriostatic water before use. Typically rated for 90 days refrigerated from the date of manufacture, though the compounding pharmacy's batch-specific certificate of analysis should specify the stability window.
Reconstituted vials (already mixed): Once the powder is dissolved, the reconstituted solution is typically stable for 28–30 days refrigerated. Some pharmacies ship pre-mixed; others ship lyophilized with instructions to mix yourself. Check your pharmacy's labeling.
Regardless of form, the principle is the same: peptides in solution degrade over time, faster at higher temperatures.
Signs of Degraded or Expired Tirzepatide
Degraded tirzepatide may look different from fresh product:
- Color change: Fresh tirzepatide solution is colorless to slightly yellow. If it has become notably yellow, cloudy, or has visible particles, discard it.
- Reduced efficacy: If you're using a pen approaching its expiration date (or past in-use limits) and your appetite suppression seems blunted, peptide degradation is one possible explanation.
- Reconstituted compounded vials: Cloudiness or visible particles that weren't there at the start suggest contamination or degradation.
There's no safety risk known to be associated with degraded tirzepatide specifically — the breakdown products of GLP-1 receptor agonist peptides aren't toxic in the way that, say, degraded tetracycline is. The primary risk is reduced or absent efficacy.
Practical Storage Guide
| Situation | What to do |
|---|---|
| New pen, not yet opened | Refrigerate at 36–46°F until ready to use |
| Pen you're currently using | Can stay at room temp (≤86°F) up to 30 days; refrigerate if you want to extend to 90 days |
| Pen left in a hot car | If temperature exceeded 86°F for more than 4 hours, contact your pharmacy or Lilly's patient support line |
| Pen accidentally frozen | Discard — do not use |
| Pen past expiration date | Discard — Lilly's stability guarantee has lapsed |
| Compounded vial (lyophilized) | Refrigerate; reconstitute only when ready to use; use within the pharmacy's labeled window once reconstituted |
What If You're Running Low?
If your pen is nearing its in-use expiration and you're mid-supply, the dose you get from the pen won't change because it's dispensed by the pen's mechanism, not by how much solution remains. Autoinjector pens deliver the labeled dose per click until the pen is empty.
If you're rationing or stockpiling pens and are concerned about expiration timing, consult with your prescriber about your refill schedule. Tirzepatide pens are filled with multiple doses — running out before the pen expires is more common than having unexpired pens go to waste.