28 days. That is the most a vial of compounded semaglutide lasts once opened. FDA recommends discarding a multi-dose vial 28 days after first use[3]. That holds even if medicine remains[3].
Semaglutide is injected once a week. So 28 days is 4 doses. The vial size does not change that.
The 28-day clock
The limit is about contamination. FDA says the risk of contamination rises after 28 days[3]. It tells patients not to follow a compounder’s longer date[3]. It also says to use a new sterile needle and syringe for each dose[3].
FDA gives the 28-day advice for multi-dose vials of sterile medicines in general[3]. The tirzepatide version is in how long a vial of tirzepatide lasts.
Brand semaglutide comes in pens
Neither the Wegovy nor the Ozempic label lists a vial. Wegovy comes as single-dose pens, single-dose syringes, or a FlexTouch pen[1]. Each single-dose pen is used once and thrown away[1].
The FlexTouch pen holds four 2.4 mg doses[1]. After first use, it keeps for up to 56 days[1]. Ozempic pens also hold several weekly doses. After first use, an Ozempic pen keeps for 56 days[2].
A Wegovy box holds 4 single-dose pens, a 28-day supply[4]. Its standard self-pay price is $349, the same at every dose up to 2.4 mg[4]. The full ladder is in Wegovy cost.
What four weekly doses use
The Wegovy label starts at 0.25 mg a week. It steps up every four weeks to 2.4 mg[1]. Four weekly doses at each step use this much:
| Weekly label dose | Used in 4 weeks | Wegovy box | Per milligram |
|---|---|---|---|
| 0.25 mg | 1 mg | $349 | $349 |
| 0.5 mg | 2 mg | $349 | $174.50 |
| 1 mg | 4 mg | $349 | $87.25 |
| 1.7 mg | 6.8 mg | $349 | $51.32 |
| 2.4 mg | 9.6 mg | $349 | $36.35 |
One flat box price spreads across more milligrams as the dose rises. Per milligram, it runs from $349 at the first step to $36.35 at 2.4 mg. A compounded vial works the same way. Only four doses of it count.
Against the compounded month
$187
Typical compounded injection month (380 sellers)
$76
Lowest published compounded month
28 days
FDA's limit on an opened multi-dose vial
Sellers bill by the month. The vial’s clock is also a month. Seller prices were read through September 2026.
Ask each seller three things. How many milligrams are in the vial? What weekly dose does the price assume? How many vials ship each month? A vial priced as two months but opened once is a one-month vial.
Compare sellers per milligram with the cost-per-mg calculator, or on the lowest cost per mg board. The monthly market by dose is in compounded semaglutide cost. Storage between doses is covered in how to store peptides.