In July 2024 the FDA warned that people using compounded semaglutide had injected 5 to 20 times the dose they meant to take. Some went to the hospital. The cause was not a bad batch. It was a mix-up between milligrams, milliliters and the "units" printed on an insulin syringe, plus vials that come in different strengths. Below: what the FDA reported, why the mistake is easy to make, what changed when the shortages ended, and how to check a dose. Where we do arithmetic ourselves, we say so.
On July 26, 2024, the FDA posted an alert about dosing errors with compounded semaglutide injections (FDA alert). A compounded drug is one a pharmacy makes itself. These products came in multiple-dose vials, which the patient draws from with a syringe.
The FDA described two kinds of error:
The examples are specific. Patients were told to draw 5 units (0.05 mL) with a U-100 insulin syringe and drew 50 units instead. One provider meant to prescribe 0.25 mg (5 units) and wrote 25 units, and the patient had severe vomiting. Another wrote 20 units instead of 2 units, and three patients got 10 times the intended dose.
Reported harms included nausea, vomiting, stomach pain, fainting, headache, migraine, dehydration, acute pancreatitis and gallstones. The FDA's broader page on unapproved GLP-1 drugs repeats the warning and adds that it has also received reports linked to compounded semaglutide or tirzepatide prescribed above label doses, given more often, or increased faster than the label allows (FDA concerns page).
Three different numbers describe the same shot, and mixing them up is the whole problem.
So the same 0.25 mg dose is a different number of units on every vial strength. Here is our arithmetic for a U-100 syringe (units = mg ÷ mg/mL × 100):
| Vial strength | Volume for 0.25 mg | U-100 syringe units | Volume for 1 mg | U-100 syringe units |
|---|---|---|---|---|
| 1 mg/mL | 0.25 mL | 25 | 1 mL | 100 |
| 2.5 mg/mL | 0.1 mL | 10 | 0.4 mL | 40 |
| 5 mg/mL | 0.05 mL | 5 | 0.2 mL | 20 |
The same 0.25 mg is 25 units on a 1 mg/mL vial and 5 units on a 5 mg/mL vial. Draw 25 units from the 5 mg/mL vial and you get 1.25 mg, five times the dose. That matches the FDA's provider example, where 0.25 mg was meant as 5 units (which implies a 5 mg/mL vial, our arithmetic) and 25 units was written.
The FDA alert notes that strengths vary between compounders, and that one compounder may sell several strengths. A refill can come at a new strength. If the units stay the same while the strength changes, the dose changes. Our semaglutide units chart and tirzepatide units chart lay out each dose at each common vial strength.
The FDA said some patients got syringes much larger than their dose needed. Stopping at 5 on a barrel that runs to 100 is easy to get wrong.
There is a second trap. Insulin syringes come in U-100 and U-40. On a U-40 syringe, 40 units equals 1 mL, so each unit mark holds 2.5 times as much liquid as a U-100 mark. Instructions written in U-100 units and drawn in a U-40 syringe give 2.5 times the intended volume (our arithmetic). Our guide to U-40 vs U-100 syringes shows how to tell them apart.
For comparison, the Zepbound label covers its own approved vials. It tells prescribers to have patients use a syringe suited to the dose, for example a 1 mL syringe that can measure a 0.5 mL or 0.6 mL dose, and to use a new syringe and needle every time (Zepbound label, 2.4). Its 2.5 mg multi-dose vial is labeled 10 mg/2.4 mL (4.17 mg/mL), four doses of 0.6 mL each (Zepbound label, 3), so the dose is stated in both mg and mL.
Published poison center data line up with the FDA reports. A 2023 case series from one regional poison center described three people who had problems after taking compounded semaglutide for weight loss. Two had taken 10-fold dosing errors. All three had nausea, vomiting and stomach pain, mostly lasting for days. One patient got a vial and syringes with no pharmacist counseling, and one dosed in milliliters and units rather than milligrams (Lambson 2023).
Two larger studies counted all GLP-1 calls, not just compounded products:
The FDA itself says that as of May 31, 2026 it had received 990 adverse event reports tied to compounded semaglutide and more than 730 tied to compounded tirzepatide. It also says these are likely undercounted, because state-licensed pharmacies that are not outsourcing facilities do not have to report adverse events to the FDA (FDA concerns page).
Compounding pharmacies fall into two groups. 503A pharmacies are state-licensed pharmacies that compound for an individual patient's prescription. 503B outsourcing facilities register with the FDA and must follow manufacturing quality rules (CGMP). The 503A vs 503B glossary entry and compounding pharmacy entry explain the split.
Normally neither may regularly copy an approved drug, but a drug on the FDA's shortage list can be copied under certain conditions. Semaglutide and tirzepatide injections were both in shortage from 2022. Here is how that ended, from the FDA's own timeline (FDA compounding update):
| Date | What FDA did |
|---|---|
| Oct 2, 2024 | Said the tirzepatide injection shortage was resolved |
| Dec 19, 2024 | Re-evaluated and again found the tirzepatide shortage resolved |
| Feb 18, 2025 | End of the tirzepatide grace period for 503A pharmacies (it ended after a court ruling on March 5, 2025) |
| Feb 21, 2025 | Said the semaglutide injection shortage was resolved |
| Mar 19, 2025 | End of the tirzepatide grace period for 503B outsourcing facilities |
| Apr 22, 2025 | Planned end of the semaglutide grace period for 503A pharmacies (it ended after a court ruling on April 24, 2025) |
| May 22, 2025 | End of the semaglutide grace period for 503B outsourcing facilities |
| Apr 1, 2026 | Reminded compounders that neither drug is on the shortage list or the 503B bulks list |
In its April 2026 update, the FDA reminded compounders that 503B facilities cannot compound from bulk drug ingredient unless the ingredient is on the 503B bulks list or the drug is on the shortage list, and that tirzepatide and semaglutide are on neither. For 503A pharmacies, the FDA said it does not intend to act against a pharmacy that fills four or fewer prescriptions of an "essentially a copy" product in a calendar month.
None of this made compounded versions FDA approved. The FDA does not review compounded drugs for safety, effectiveness or quality before they are sold, and it says they should only be used when a patient's needs cannot be met by an approved drug.
From the FDA's page on unapproved GLP-1 drugs (FDA concerns page):
The FDA's advice is to ask your prescriber or the compounder how to measure your dose, and it asks them to give you a syringe that fits the dose and to show you how to use it. In practice, that means you should be able to say your dose three ways before it goes in:
If the three do not agree, or if a new vial has a new strength, stop and call the pharmacy or prescriber before you inject. You can use the reconstitution calculator to see the math, but the person who prescribed and dispensed the drug should confirm it.
Dose Track is built around the same idea. When you add an already-mixed vial, you enter its total mg and total mL, and each dose you log in mg shows the matching mL and syringe units, so the number you draw sits next to the number you were prescribed. It also tracks what is left in each vial. It does not recommend doses.
The Wegovy label says overdose with GLP-1 drugs has caused severe nausea, severe vomiting and severe low blood sugar. It suggests contacting the Poison Help line (1-800-222-1222) or a medical toxicologist, and says a long period of watching and treatment may be needed because semaglutide's half-life is about 1 week (Wegovy label, 10). The Zepbound label gives the same phone number and notes tirzepatide's half-life of about 5 days (Zepbound label, 10). If you have severe symptoms, get emergency care.
This article is general information, not medical advice. Talk to your prescriber before you start, change or stop any medicine.