Quick answer: once a multiple-dose vial has been opened or punctured, the general rule is to date it and discard it within 28 days, unless the manufacturer's label gives a different date for that opened vial. For a compounded multi-dose vial, use the pharmacy's beyond-use date (BUD) or 28 days after first puncture, whichever comes first; the FDA recommends discarding compounded GLP-1 multi-dose vials within 28 days of first use even if the compounder's instructions say longer. The shorter date always wins, and no date ever goes past the printed expiration date.
Twenty-eight days is a ceiling for contamination risk, not a promise that the contents are still potent. A label or pharmacist can give you a shorter window, and a vial with no published data doesn't automatically get the full 28 days.
Educational only, not medical advice. This article explains labeling and pharmacy standards. Your product's label and your pharmacist's instructions always come first. It doesn't recommend any dose, product or mixing method.
Where does the 28-day rule come from?
It comes from the US Pharmacopeia's sterile-compounding standard, USP General Chapter <797>. As the CDC summarizes it:
- An unopened multi-dose vial is discarded according to the manufacturer's expiration date.
- Once a multi-dose vial is opened (for example, needle-punctured), it "should be dated and discarded within 28 days unless the manufacturer states another date for that opened vial."
- The beyond-use date "should never exceed the manufacturer's original expiration date."
The reason is contamination. Every puncture is a chance for microbes to get in. Multi-dose vials usually contain a preservative, but the CDC notes the preservative "does not have an effect on viruses nor does it provide complete protection against bacterial contamination."
Which date applies to your vial?
| What you have | The date to use | Source |
|---|---|---|
| A manufactured multi-dose vial (for example, bacteriostatic water) | 28 days after first puncture, unless its label says otherwise | USP <797>, as summarized by the CDC |
| A compounded multi-dose vial from a pharmacy | The pharmacy's BUD or 28 days after first puncture, whichever is shorter | USP <797> |
| A compounded GLP-1 multi-dose vial | Within 28 days of first use, even if medication remains and even if the instructions say longer | FDA |
| A brand-name product with its own in-use limit | The label's limit, which may be shorter or longer than 28 days | The product's prescribing information |
| A vial you reconstituted yourself with no label guidance | Ask your pharmacist; don't assume 28 days | See below |
When the label says something different
Manufacturers can set their own in-use limits, and they vary. Some examples from US labels:
- Zepbound multi-dose vial or KwikPen: "Throw away opened multi-dose vial or single-patient-use KwikPen after a total of 30 days at room temperature, 30 days after first use, or after taking 4 weekly doses, even if there is medicine left in it."
- Zepbound single-dose vial: "Throw away all opened vials after use, even if there is medicine left in the vial." Single-dose vials don't get 28 days at all.
- EGRIFTA WR (tesamorelin), which is mixed before use: "Discard unused solution of EGRIFTA WR vial 7 days after mixing."
- EGRIFTA SV (tesamorelin): used "immediately following reconstitution," and any unused solution is thrown away.
- Ozempic (semaglutide) pens can be used for 56 days after first use, per its label. That's a pen, not a vial, and the number belongs to that product only.
The pattern: the label for your exact product sets the date. If it gives one, that's your limit, even when it's shorter than 28 days.
What about a vial you mixed yourself?
For a vial you reconstituted from powder, the 28-day rule only caps the contamination risk of repeated punctures. It says nothing about whether the dissolved drug stays stable that long, and research-use vials don't come with FDA-reviewed stability data. If the product's label or your pharmacist gives a use-by period, use it. If nobody has, ask a pharmacist before assuming any number, and don't rely on a figure from a forum or a different product.
The vial of BAC water you mixed it with has its own clock, too: see does bacteriostatic water need to be refrigerated after opening?
How to work out your discard date
- Write down the date of first puncture. For a vial you mix yourself, that's usually the day you reconstitute it.
- Add 28 days, or the label's in-use period if it gives one.
- Compare with the pharmacy BUD and the printed expiration date. Use the earliest of all of them.
- Write that date on the vial, not just the date you opened it. The Joint Commission's guidance on multi-dose vials makes the same point.
Calendar math only: a vial first punctured on October 19 hits its 28-day limit on November 16. If its pharmacy BUD is November 10, November 10 is the discard date.
Signs to discard a vial early
Whatever the date says, don't use a vial and ask your pharmacist if:
- It looks cloudy, discolored or has particles when it should be clear. See why a peptide can look cloudy after mixing.
- It has frozen, or been exposed to heat beyond its label.
- The stopper is damaged, or you're not sure it has stayed sterile.
- You can't remember when it was first punctured.
More on temperatures, BUDs and room-temperature allowances is in our guide to storing peptides and GLP-1s.
Running out vs timing out
A vial can reach its discard date before it's empty, especially when each draw is small. That's not a reason to stretch it: the FDA says to discard a compounded GLP-1 multi-dose vial after 28 days "even if medication remains in the vial." If this keeps happening, ask your prescriber or pharmacist whether a different vial size makes sense.
Tracking it in Caliper
Caliper's vial tracking records each vial's reconstitution or opened date, its use-by date and its printed expiry, so you can see when a vial reaches its use-by date. Caliper stores the dates you enter; it doesn't assign a BUD or decide whether a vial is still good. That's your label and your pharmacist.
FAQ
How long can I use a vial after reconstituting it?
As long as its label, pharmacy or pharmacist says, and for a multi-dose vial no longer than 28 days after first puncture unless the manufacturer specifies otherwise. If you mixed it yourself and have no guidance, ask a pharmacist rather than assuming 28 days.
What is the 28-day rule for multi-dose vials?
Under USP <797>, as summarized by the CDC, an opened or punctured multi-dose vial should be dated and discarded within 28 days unless the manufacturer states another date, and never after its expiration date.
Does the 28 days start when I mix the vial or when I first use it?
The rule counts from when the vial is first opened or punctured. For a vial you reconstitute yourself, that's usually the day you mix it.
Can a vial last longer than 28 days?
Only if its manufacturer's label says so for that opened product. Compounded multi-dose vials can't go past 28 days after first puncture under USP <797>, and the FDA recommends discarding compounded GLP-1 vials within 28 days even if instructions say longer.
My compounded vial says it's good for longer than 28 days. Which do I follow?
The FDA recommends discarding compounded GLP-1 multi-dose vials within 28 days after first use, even if the compounder's instructions say longer. Ask your pharmacy about the discrepancy.
What if there's medicine left after 28 days?
Discard it. The FDA's guidance for compounded GLP-1 vials is to throw the vial away after 28 days even if medication remains.
The takeaway
Date every vial on first puncture, and use the earliest of: the label's in-use limit, the pharmacy BUD, 28 days, and the expiration date. Twenty-eight days is a ceiling, not a target. When a vial has no guidance, ask a pharmacist before you pick a number.
Sources
- CDC, Preventing unsafe injection practices (multi-dose vials and USP <797>)
- FDA, FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss
- U.S. Pharmacopeia General Chapter <797>, as summarized in the Florida Department of Health's USP <797> (2022 revision) inspection guide
- The Joint Commission, Managing multi-dose vials
- Zepbound (tirzepatide) US prescribing information and single-dose vial instructions for use, Eli Lilly
- DailyMed, EGRIFTA SV (tesamorelin) prescribing information and EGRIFTA WR (tesamorelin) prescribing information
- Ozempic (semaglutide) prescribing information, Novo Nordisk
Make the math (and the record-keeping) automatic
Caliper is a private, local-first tracker for GLP-1 and peptide protocols. You record the amount you took and it logs each dose with one tap, reminds you when the next one is due, tracks vials with reconstitution and use-by dates, and keeps injection sites, side effects and weight trends on one timeline. Your health data stays on your device, and Caliper never recommends or calculates a dose; it organizes what you and your provider decide.
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Medical disclaimer: This article is for general educational purposes only and is not medical advice. It does not recommend any dose, dilution, compound, product, supplier or protocol. Always follow your prescriber's instructions and the product label, and talk to a pharmacist or healthcare provider about any question regarding your medication, its preparation, storage, measurement or administration.