Compounded GLP-1 Dosing Errors: Units vs. mL in FDA's Own Reports

FDA's own reports show that compounded GLP-1 overdoses usually happen at the syringe, not in the drug: patients drew up 5 to 20 times their intended semaglutide dose, often because the prescription was written in milligrams, the vial was labeled in mg/mL, and the syringe was marked in "units." Poison center data published since then point the same way, with wrong-dose errors as the single largest category.

What FDA actually reported

On July 26, 2024, FDA issued an alert to health care providers, compounders and patients about dosing errors with compounded injectable semaglutide. The agency had received adverse event reports in which patients measured and injected the wrong amount from multiple-dose vials, and others in which health care providers miscalculated the dose (FDA alert).

The details are specific. FDA said patients "administered five to 20 times more than the intended dose of semaglutide," and that provider miscalculations produced doses five to 10 times higher than intended. FDA cited "confusion between different units of measurement" as a contributor and gave one concrete example: a 5-unit dose drawn up as 50 units on a U-100 insulin syringe (FDA alert). FDA was also aware of patients receiving syringes "significantly larger than the prescribed volume."

The reported effects included nausea, vomiting, abdominal pain, fainting, headache, migraine, dehydration, acute pancreatitis and gallstones. Some patients needed medical care or were hospitalized (same source).

FDA's broader page on unapproved GLP-1s, current as of October 1, 2026, still lists dosing errors with compounded injectable semaglutide as a concern. As of May 31, 2026, it counted 990 adverse event reports tied to compounded semaglutide and more than 730 tied to compounded tirzepatide, while noting that most state-licensed pharmacies are not required to report, so the true number is likely higher (FDA). Those totals cover all kinds of problems, not only dosing errors. We break down the earlier adverse event data in our separate analysis.

Why "units" trip people up

A compounded GLP-1 prescription can involve three different measurements at once:

• Milligrams (mg): the amount of drug. Trials and approved labels describe doses this way, such as 0.25 mg or 2.4 mg of semaglutide.
• Milliliters (mL): the volume of liquid. The vial's concentration, such as "X mg/mL," links mg to mL.
• Units: the tick marks on an insulin syringe. On a U-100 syringe, the kind in FDA's example, 100 units equals 1 mL, so each unit is 0.01 mL.

"Units" on an insulin syringe were designed for insulin, where the unit is the dose. With a GLP-1 vial, a "unit" is only a volume marking, and how much drug it holds depends entirely on the vial's concentration. Two pharmacies can make the same drug at different concentrations, so the same mg dose can mean a different number of units. FDA told providers that "concentrations may vary" and to contact the compounder if unsure about a calculation (FDA alert).

Illustration of the arithmetic only, not dosing instructions. Concentrations shown are hypothetical examples. The second row mirrors the 5-unit to 50-unit error described in the FDA alert. Your prescription label and pharmacist govern your actual dose.

The table shows why these errors are so often tenfold. A single decimal slip between 0.05 and 0.5, or between 5 and 50, moves the dose by a factor of ten, and a 1 mL syringe has plenty of room for it.

What poison center data show

Early warning: a 2023 case series

Before FDA's alert, a poison center team described three patients harmed after self-injecting compounded semaglutide from a compounding pharmacy or an aesthetic spa. Two made 10-fold dosing errors. One had been given a vial and syringes with no pharmacist counseling, and one measured doses in milliliters and units instead of milligrams. All three had nausea, vomiting and abdominal pain, mostly lasting several days. The authors noted that compounded vials lack the safety features of prefilled pens (Lambson et al., Journal of the American Pharmacists Association, 2023).

National data: wrong dose is the top error

A 2026 study in the Journal of Medical Toxicology analyzed 10,033 GLP-1 exposures reported to the National Poison Data System from 2012 to 2023. Exposures rose from 3,113 before July 1, 2021, to 6,920 after, a 2.2-fold increase after semaglutide's approval for weight management (Miller et al., J Med Toxicol). Most were unintentional therapeutic errors. Wrong-dose errors were the most common, at 5,171, followed by wrong-time errors at 1,160, such as injecting daily instead of weekly or starting at a full dose instead of titrating (Drug Topics summary).

That study covers all GLP-1 products and ends in 2023, so it cannot separate compounded from branded products. A regional poison center fills in some of that gap.

The compounded share

The Washington Poison Center reports that many patients have accidentally taken "10-fold overdoses," and that about half of its GLP-1 calls involve compounded semaglutide or tirzepatide. It points to the format: these products are dispensed as vials, not pens, and patients are often confused by dosing in units "like insulin instead of milliliters" (Washington Poison Center). The center says 10-fold overdoses usually cause severe nausea, vomiting and food intolerance, sometimes requiring prescription antiemetics and IV fluids, and that long-term effects of these one-time overdoses are unknown.

The pattern is not limited to the U.S. The Netherlands' national poison center logged 149 reports involving injectable weight-loss drugs in 2025, up from 76 the year before (NL Times).

Source: FDA, JAPhA, J Med Toxicol, Washington Poison Center, FDA.

Why pens and single-dose vials avoid the problem

Approved semaglutide pens remove the arithmetic. The Ozempic label describes pens that deliver set doses, such as 0.25 mg or 0.5 mg from one pen and 1 mg or 2 mg from others, plus single-dose prefilled syringes (Ozempic prescribing information). The patient selects a dose rather than calculating a volume.

Some approved products do use a vial and syringe. Lilly sells Zepbound in single-dose vials, with instructional materials on giving the medicine by needle and syringe (Lilly press release). A single-dose vial holds one dose, which is a different situation from a multiple-dose compounded vial where each week's dose must be measured out of a larger supply.

Medication-safety experts have seen this pattern before. In 2013, the Institute for Safe Medication Practices flagged concentrated U-500 insulin being measured with the wrong type of syringe, "introducing the possibility of 5-fold dosing errors," and urged that doses be explained in both actual amount and syringe markings (Drug Topics, reporting ISMP). Compounded GLP-1 vials recreate that mismatch for a new population of patients.

What FDA asks compounders, prescribers and patients to do

FDA's recommendations are short. Compounders and providers should give patients the "appropriate syringe size for the intended dose" and counsel them on measuring with it. Providers should stay alert to differing concentrations and confirm calculations with the compounder when unsure. Patients should talk with their provider or compounder about how to measure and give the intended dose (FDA alert).

In practice, that translates into a few questions worth asking your pharmacist or prescriber before the first injection:

• What is my dose in milligrams, and what is that in milliliters and syringe units for this specific vial?
• What is this vial's concentration, and will it stay the same on refills?
• Does the syringe I was given match the size my dose needs?
• When my dose increases, who recalculates the units, and will I get it in writing?

The bottom line for patients

The documented risk with compounded GLP-1 vials is largely a measurement risk, and it is predictable. FDA, poison centers and pharmacists describe the same tenfold slips, the same unit confusion and the same missing counseling. If you use a compounded product, the most protective step in FDA's guidance is a clear, written mg-to-units conversion for your exact vial, checked with your pharmacist. If you would rather avoid conversions entirely, ask your prescriber whether an approved fixed-dose pen fits your situation and budget.

Sources

1. FDA: FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products (July 26, 2024)
2. FDA: FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss
3. Lambson JE, et al. Administration errors of compounded semaglutide reported to a poison control center: case series. J Am Pharm Assoc. 2023
4. Miller J, et al. National Poison Center Trends in GLP-1 Receptor Agonist Exposures Following FDA Approval for Weight Loss. J Med Toxicol. 2026
5. Drug Topics: Data show rise in GLP-1 poison center calls tied to dosing errors
6. Washington Poison Center: GLP-1 exposures on the rise
7. NL Times: Poisonings from injectable weight-loss drugs double in the Netherlands
8. Ozempic (semaglutide) injection prescribing information
9. Eli Lilly: Zepbound single-dose vials press release
10. Drug Topics: Dosage errors common with Humulin R U-500 insulin (ISMP, 2013)

Medical disclaimer: This article is general information, not medical advice, and does not replace a licensed clinician who knows your history. Approvals, labels, coverage and prices change; check the linked sources and talk with your prescriber or pharmacist before making decisions about any medication.