Last updated: June 2026 · Reviewed June 2026 · Built by the InjectBuddy team
When should you discard an opened vial? the 28-day rule explained
Discard an opened multi-dose vial 28 days after the first needle puncture of the stopper, or on the manufacturer's stated beyond-use date if that arrives sooner — whichever date comes first is your hard limit. This guide explains where the 28-day rule comes from, how to calculate the exact discard date for any open date, how different vial types are treated, and answers the questions people ask most.
- 28 days from first puncture is the default beyond-use date (BUD) for a preserved multi-dose vial, per CDC/USP <797>.
- The discard date never goes past the printed manufacturer expiry — whichever comes first wins.
- Single-dose vials have no 28-day window: use once, discard immediately, even if liquid remains.
- Write the open date on the label the moment you puncture it; the discard date is open date + 28 days.
- Working out a draw volume for that vial? Use the Testosterone (TRT) dose calculator to convert your mg dose into syringe units.
Why 28 days, and where the rule comes from
A multi-dose vial is built to be entered more than once: it contains an antimicrobial preservative (benzyl alcohol in testosterone cypionate, metacresol or phenol in some peptides) that slows bacterial growth between draws. That preservative is the reason a multi-dose vial gets a 28-day grace period at all — a single-dose vial has none. CDC guidance, citing United States Pharmacopeia General Chapter <797>, states an opened multi-dose vial "should be dated and discarded within 28 days unless the manufacturer states another date for that opened vial," and that the beyond-use date "should never exceed the manufacturer's original expiration date."
The preservative is not magic. It slows growth; it does not sterilise. It has no effect on viruses, and it does nothing if a used needle re-enters the vial. So the 28-day clock assumes clean technique on every draw — a fresh sterile needle and syringe each time. Reusing equipment has caused real hepatitis B and C outbreaks traced to shared and mishandled vials, which is why the discard date is a hard stop, not a suggestion.
One nuance people miss: 28 days is the default, not a ceiling. Some labels specify shorter (a few compounded GLP-1 products say 28 or fewer days; some reconstituted peptides recommend tighter windows once mixed). When the label and the 28-day default disagree, the label wins. The rule is "28 days or the manufacturer's stated date, whichever is sooner."
Vial type → discard rule
| Vial type | Discard rule once accessed | Counts from |
|---|---|---|
| Multi-dose, preserved | 28 days, or label BUD if shorter | First puncture |
| Single-dose / single-use | Discard immediately after one use | First puncture (no window) |
| Reconstituted peptide (you added water) | Per label; commonly 28 days refrigerated, often less | Day of mixing |
| Manufacturer pen (e.g. GLP-1) | Label-specific in-use days (often 14–56) | First use |
| Any vial past printed expiry | Discard — expiry overrides the 28-day window | Printed expiry date |
The single biggest error is treating every glass vial as a multi-dose vial. If the label says "single dose" or "single use," there is no 28-day window: one draw, then it goes in the sharps bin, leftover liquid and all. The preservative-free formulation has nothing to hold contamination back.
How the discard date is calculated
The arithmetic is deliberately boring: discard date = open date + 28 days, then capped at the printed expiry. Day zero is the day of first puncture. If you puncture on the 1st, day 28 lands on the 29th of the same month for a 31-day month, so count carefully across month boundaries rather than assuming "same date next month."
To label it, write the open date and the discard date directly on the vial with a fine permanent marker, away from the dose/strength printing so you do not obscure it. Many people write only the discard date to remove the mental arithmetic at draw time. If your printed expiry is closer than 28 days away, write the expiry as the discard date instead.
Open a multi-dose testosterone vial on 1 March. 1 + 28 = discard on or before 29 March. Label: "Opened 1 Mar · Discard 29 Mar."
Open on 20 June. June has 30 days, so 10 days reach 30 June; the remaining 18 days land on 18 July. Discard date = 18 July, not 20 July.
Vial printed expiry is 15 April. You open it on 1 April. Open + 28 = 29 April, but expiry (15 April) is sooner, so the real discard date is 15 April.
A 1 mL single-dose vial drawn for one 100 mg shot: discard immediately after the draw even though ~0.5 mL remains. The 28-day rule does not apply to single-dose vials.
You add 2 mL bacteriostatic water (a preservative) to a 5 mg peptide vial on 3 May. Treat the mixing day as day zero: discard by 31 May (3 + 28), refrigerated, unless the supplier specifies less.
A 10 mL, 200 mg/mL vial holds 2,000 mg. At 100 mg/week you would use it over 20 weeks, but the open vial must be discarded at 28 days regardless of remaining volume — so ~1,600 mg is binned. Buy a smaller vial if your weekly use is low.
Open on 14 February 2028 (a leap year). 15 days reach 29 February; 13 more land on 13 March. Discard date = 13 March 2028.
Labelling the open date in practice
A discard date only works if it is visible. The habit that prevents waste and accidental use is: puncture, then immediately write the date. Do not rely on memory or a phone note that gets lost — the vial itself should carry the answer. If two people share a household fridge of medication, an undated vial is effectively expired, because nobody can prove when it was opened.
If you are also tracking how long a vial physically lasts at your dose, that is a separate calculation from the discard date. The discard date caps usability at 28 days; the volume calculation tells you whether you will even reach that cap. When the two disagree — a big vial used slowly — the 28-day cap always wins and the remainder is discarded.
So, when should you discard an opened vial?
Discard an opened multi-dose vial 28 days after the first needle puncture, or on the manufacturer's stated in-use date if that is sooner — the rule is "28 days or label date, whichever comes first." Single-dose vials have no window at all: one draw, then straight to the sharps bin. Write the open date on the vial the moment you puncture it so the discard date (open date + 28 days) is always visible. To track how many draws remain before that date, use the Testosterone (TRT) dose calculator to see exactly how much volume each dose uses.
FAQs
When should you discard an opened vial?
Does the 28-day clock start at manufacture or at opening?
Can I use a multi-dose vial past 28 days if it still looks fine?
Why discard a single-dose vial straight away when liquid is left?
What if my label says a different number of days?
Sources
- CDC. Preventing Unsafe Injection Practices (multi-dose vial 28-day discard rule, citing USP <797>). cdc.gov, 2024.
- CDC. Safe Injection Practices to Prevent Transmission of Infections to Patients. cdc.gov, 2024.
- DailyMed (FDA). DEPO-Testosterone (testosterone cypionate) 200 mg/mL multiple-dose vial, benzyl alcohol preservative. dailymed.nlm.nih.gov, 2025.
- Guh AY, et al. CDC Grand Rounds: Preventing Unsafe Injection Practices in the U.S. Health-Care System. MMWR, 2013.
- Manchikanti L, et al. Assessment of infection control practices for interventional techniques. PubMed PMID 22996856, 2012.
This guide is for general educational purposes only and does not constitute medical advice. Discard dates and beyond-use dating vary by product — always follow the specific label and your prescriber or pharmacist.