What Is in a Compounded GLP-1 Vial: How to Read the Label

An approved GLP-1 pen delivers a dose. A compounded vial delivers a concentration, and someone has to turn that concentration into a dose. When the vial arrives by mail, that someone is usually you. FDA has collected reports of what happens next: patients who administered five to twenty times what was intended, some of whom sought medical attention or were hospitalized.

Concentration is not dose

A dose is an amount of drug, written in milligrams. A concentration is how tightly that drug is packed into liquid, written in milligrams per milliliter. A vial labeled 2 mg/mL holds two milligrams of drug in every milliliter of solution. A vial labeled 5 mg/mL holds two and a half times as much in the same milliliter. Both vials can fill the same prescription. They cannot do it with the same volume.

The approved products removed this problem by fixing both numbers. FDA describes Wegovy as single-dose pre-filled pens that deliver a preset dose once weekly, Ozempic as multiple-dose pre-filled pens designed for once-weekly dosing, and Rybelsus as an oral tablet.^[1] The pen holds the concentration constant and does the measuring, and the strength is printed on a label FDA reviewed.^[6][7] A compounded vial carries no such review: compounded drugs are not FDA-approved, and FDA does not verify their safety, effectiveness or quality before they are marketed.^[3] Nothing about the vial format is dishonest, but it moves a calculation out of the factory and onto a kitchen table.

FDA has said plainly what varies. Compounders offer semaglutide in different containers, including multiple-dose vials and prefilled syringes; concentrations may differ depending on the compounder; and a single compounder may offer several concentrations of its own.^[1] There is no standard vial. There is only the vial in front of you.

Why units are the part that catches people

Compounded GLP-1 is frequently drawn with an insulin syringe, and insulin syringes are marked in units rather than milliliters. A U-100 syringe holds one milliliter across one hundred units, so a unit on that barrel is one hundredth of a milliliter. FDA's own alert spells the conversion out in passing when it describes patients instructed to draw a five-unit dose, which it writes as 0.05 milliliters.^[1]

That is why a units instruction does not travel. If a pharmacy changes its concentration, or your prescription moves to a different pharmacy, a number of units you remember from before describes a different amount of drug, and nothing on the syringe will tell you. FDA's reports include providers who made the conversion wrong in the same direction: one meant to prescribe five units and wrote twenty-five, and another prescribed twenty units instead of two, affecting three patients who received ten times what was intended and became nauseated and vomited.^[1]

The largest group of reports was simpler and harder to guard against. Most described patients drawing up more than the prescribed dose from a multiple-dose vial during self-administration, many of them unfamiliar with measuring from a syringe at all. In several, patients directed to give five units on a U-100 syringe gave fifty.^[1] In one, a patient could not get clear dosing instructions from the telemedicine provider who wrote the prescription, searched online for medical advice, and took five times the intended amount.^[1]

Reported consequences included nausea, vomiting, abdominal pain, fainting, headache, migraine, dehydration, acute pancreatitis and gallstones, with some patients hospitalized. Semaglutide's half-life is about a week, so FDA notes that observation and treatment after an overdose may need to be prolonged.^[1]

Two vials, one prescription, different volumes

Put the two facts together and the practical trap appears. Suppose your prescription is unchanged and your pharmacy changes, or your pharmacy reformulates. If the new vial is twice the concentration of the old one, the same prescribed milligram amount now lives in half the volume, and therefore in half the number of syringe units. Drawing to the mark you are used to would deliver twice the drug.

This is not a reason to recalculate anything yourself. It is the reason a new vial is a new conversation. When the box changes, the number on the syringe is the last thing to assume is unchanged, and the pharmacy that prepared it is obliged to tell you how it is meant to be measured. FDA's advice to patients is exactly that: talk to your health care provider or compounder about how to measure and administer the intended dose.^[1]

What the label should state

Federal law sets an explicit list for drugs from a 503B outsourcing facility. Under 21 U.S.C. 353b(a)(10), the label must carry the statement “This is a compounded drug” or a comparable statement identifying it as one, the name and address and phone number of the outsourcing facility, and for the drug itself the lot or batch number, the established name, the dosage form and strength, the statement of quantity or volume, the date it was compounded, the expiration date, storage and handling instructions, the National Drug Code if there is one, the statement “Not for resale”, and a list of active and inactive ingredients with the quantity or proportion of each.^[2]

That list is a fair description of what a complete label looks like. It is worth knowing that it binds outsourcing facilities specifically. A 503A pharmacy compounding for one identified patient works to state board requirements and USP standards instead, and there is no equivalent federal enumeration for the vial it sends you. Which route your seller is using is a question we take apart in which GLP-1s can be compounded, and the pharmacy behind each seller we can trace is in our pharmacy register.

• The strength, as a concentration. Milligrams per milliliter, and the total volume in the vial. This is the number that changes what a syringe unit means.
• Every ingredient, active and inactive. If a vitamin or a preservative is in there, it belongs on the label with its own quantity.
• A lot or batch number. Without it a recall cannot reach you and a complaint cannot be traced.
• The date compounded and the beyond-use date. Two dates, not one.
• Storage and handling instructions, including whether it is refrigerated and what to do if it was not.
• The pharmacy's name, address and telephone number. If the vial names no pharmacy, you cannot verify anything about who made it — see how to verify an online GLP-1 pharmacy.

Beyond-use dating is not an expiration date

A manufactured drug carries an expiration date supported by stability testing of that product in that container. A compounded preparation carries a beyond-use date, which USP defines as the date or time after which the preparation may not be stored or transported, calculated from the date or time of compounding.^[4] It is a limit on the preparation, set by the pharmacy, and it is generally much shorter than an expiration date because it has to account for chemical degradation, microbial growth and the integrity of the container all at once.^[4]

The standards that govern how those dates are assigned, USP General Chapters <795>, <797>, <800> and <825>, became official on November 1, 2023.^[5] For sterile preparations the permitted dating depends heavily on the conditions the pharmacy compounded under and on what testing it performed, which is why two pharmacies can lawfully assign very different dates to superficially similar vials.

Read your two dates as two different pieces of information, and read the storage line with them. A beyond-use date assumes the storage conditions on the label were kept. If a shipment sat warm, or arrived without a cold pack that the label implies it should have had, that is a call to the pharmacy rather than a judgment call for you.

What B12 and other additions change

Many compounded vials contain more than the GLP-1. FDA has stated it is aware of compounders adding cyanocobalamin (vitamin B12), pyridoxine (vitamin B6), levocarnitine and nicotinamide adenine dinucleotide to semaglutide products, and that the safety and effectiveness of combining semaglutide with other ingredients has not been established.^[1] No approved semaglutide injection contains a vitamin at all. We go through the three explanations offered for the B12 pairing, and which of them has a document behind it, in why compounded semaglutide is mixed with B12.

For label reading, a combination vial does one specific thing: it puts a second number on the label. The concentration of the GLP-1 and the concentration of the added ingredient are separate figures, and a milligram figure printed alone can belong to either. If your label carries a strength that does not identify which ingredient it describes, that ambiguity is the pharmacy's to resolve, not yours.

When the label and the instructions disagree

Do not reconcile it yourself. Photograph the vial label, the carton and any instruction sheet, then contact both the pharmacy named on the label and the clinician who wrote the prescription, and do not inject until they agree. This is not caution for its own sake. Every error pattern FDA documented began with a patient or a provider deciding a number in private.^[1]

1. Stop before the injection. A missed timing question is a question for the prescriber; a wrong amount cannot be taken back.
2. Photograph everything, including the lot number and both dates.
3. Call the pharmacy named on the label and ask what concentration this vial is and how the prescribed amount is meant to be measured from it.
4. Call the prescriber and confirm the prescription against what the pharmacy said.
5. Report it to FDA through MedWatch if a dosing error or an adverse event occurred. FDA asks patients, providers and compounders alike to report these.^[1]