Compounded GLP-1 Vials vs Pens: Dosing, Units and Supplies

Last updated November 11, 2026 · Reviewed by the Gala Health team

Vial vs pen at a glance

	Brand-name pen	Compounded vial
How the dose is set	Fixed by the pen strength	You measure it with a syringe
What you need to know	Which pen strength you were prescribed	Dose in mg, concentration in mg/mL and volume in mL (or units)
Changing the dose	A new pen strength	Often the same vial, a different volume, as your prescriber directs
Doses per container	Single-dose pens, or a multi-dose pen for some brands	Usually several doses per vial
FDA approval	Yes, for its label uses	No. Compounded medications are not FDA-approved

Brand-name tirzepatide also comes in vials. The Zepbound® label lists single-dose pens and single-dose vials that hold 0.5 mL, plus a multi-dose vial and a KwikPen that each hold 4 doses. Wegovy® injection comes in pens. So vial vs pen is about the device, not only brand vs compounded.

Vial dosing math: mg, mL and units

Three numbers describe a vial dose. The dose is the amount of medicine, in milligrams (mg). The concentration, printed on the vial label, is how many mg are in each milliliter (mg/mL). The volume is how much liquid you draw. Insulin-style syringes are often marked in units, and on a U-100 syringe 100 units equal 1 mL.

Volume in mL = dose in mg ÷ concentration in mg/mL.
Units on a U-100 syringe = volume in mL × 100.

Example only	Dose	Concentration	Volume	U-100 units
Semaglutide	0.25 mg	2.5 mg/mL	0.1 mL	10 units
Tirzepatide	2.5 mg	10 mg/mL	0.25 mL	25 units

These are arithmetic examples, not dosing instructions. Concentrations differ between pharmacies and can change between shipments, so the same number of units can mean a different dose. Use only the dose, concentration and syringe on your own prescription and pharmacy label.

The FDA says it has received reports of adverse events, some requiring hospitalization, that may be related to dosing errors with compounded semaglutide, where patients measured and injected the wrong dose or health care professionals miscalculated it. Get your dose in writing, in the same unit as your syringe markings, and message Gala's care team before your first injection if any number does not match.

Injection supplies for a vial

A syringe sized for your dose. The Zepbound label tells vial users to use a syringe appropriate for the dose, for example a 1 mL syringe that can measure 0.5 mL or 0.6 mL.
A new sterile needle and syringe for every dose. The FDA warns that reusing them can contaminate the medicine.
A sharps container for used needles and syringes.
Fridge space: injectable GLP-1 medicines need refrigeration as their labels or pharmacy instructions direct.

Gala includes a home injection kit with your medication, so you are not left to buy supplies separately. For the steps of an injection and sharps disposal, see how to inject a GLP-1.

The 28-day rule for multi-dose vials

The FDA recommends that multi-dose vials of sterile medicine be used within 28 days after first use, because the contamination risk rises after that. Its advice to patients is to discard the vial 28 days after first use even if medicine remains, and not to keep using it past 28 days even if the compounder's instructions say longer. Write the date you first pierce a vial on its label.

Is a vial harder than a pen?

It takes one more step: drawing the dose. Once your dose, concentration and syringe are clear, the injection itself is the same: once a week, under the skin of the stomach or thigh, or the upper arm (the Zepbound label says the back of the upper arm should be injected by another person). A vial also lets your provider move you to a new dose without a new device, and Gala includes every dose level in your plan price, so a higher dose does not cost more. See does the GLP-1 price go up with the dose.

Gala offers compounded semaglutide, compounded tirzepatide and brand-name Ozempic®. A licensed provider reviews your online assessment and prescribes only if it is appropriate for you. If prescribed, your medication and injection kit ship free, and you can log every shot and message your care team in the Gala GLP-1 app. Start your online GLP-1 assessment, or read more about compounded GLP-1 medications.

This article is for information only and is not medical advice. If the number on your instructions does not match your syringe, stop and ask your provider or pharmacy before injecting.

Frequently asked questions

Does compounded semaglutide or tirzepatide come in pens?

Compounded semaglutide and tirzepatide usually come in vials that you draw into a syringe. Gala ships compounded GLP-1 as vials with a home injection kit included. Brand-name Wegovy comes in pens, and brand-name Zepbound comes in pens, vials and a KwikPen.

How many units is my compounded dose?

It depends on your vial's concentration. Volume in mL equals your dose in mg divided by the concentration in mg/mL, and on a U-100 syringe each 0.01 mL is 1 unit. Always use the dose and units on your own prescription and pharmacy label, and ask your provider if anything is unclear.

Can I reuse a syringe or needle?

No. The FDA says to use a new, sterile needle and syringe for each dose, because reusing them can contaminate the medicine. The Zepbound label gives the same instruction for vial users.

How long is a compounded GLP-1 vial good for after opening?

The FDA recommends discarding a multi-dose vial 28 days after first use, even if medicine remains and even if the compounder's instructions say it can be used longer. Follow the storage directions on your pharmacy label as well.

Is a vial less accurate than a pen?

A pen delivers a fixed dose, while a vial dose depends on measuring the right volume. Accuracy comes from knowing your dose in mg, your concentration and your syringe markings, and from asking before your first injection if any number does not match.

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Sources

This article is for general information and is not medical advice. Talk to a licensed provider about your own health.

Compounded GLP-1 Vials vs Pens: How Vial Dosing Works