Guide / avoiding mistakes

Common GLP-1 Dosing Mistakes

The FDA’s alert on compounded semaglutide describes overdoses of five to 20 times the intended dose, caused by mixing up mg, mL and units or by using syringes that were too big. The fix is to write out the strength math step by step and read the exact lines printed on your syringe.

Last updated September 30, 2026

If your medicine came from a pharmacy vial

Compounded semaglutide or tirzepatide: what the FDA says

“Compounded” means a pharmacy made its own version instead of the brand-name product. If your semaglutide or tirzepatide came from a pharmacy in a vial, here is what matters most:

Throw the vial away 28 days after you first use it, even if its label says it lasts longer.
Use a new sterile needle and syringe for every dose.
The FDA has hundreds of reports of side effects and other problems with compounded versions, some involving doses higher than the label’s schedule.
The shortage is over. The FDA says pharmacies may no longer regularly make copies of the brand-name medicine.

The details from the FDA

The FDA says the semaglutide shortage was resolved on February 21, 2025, and the tirzepatide shortage was resolved in 2024. After each one, the FDA gave compounders a wind-down period, when it held off on enforcing its rules against compounded (pharmacy-made) copies. For semaglutide, that period ended April 22, 2025 for 503A pharmacies (standard compounding pharmacies) and May 22, 2025 for 503B outsourcing facilities (larger-scale compounders). For tirzepatide, it ended February 18, 2025 for 503A and March 19, 2025 for 503B. The FDA says 503A pharmacies may not regularly compound a drug that is “essentially a copy” of one sold commercially. Adding vitamin B12 does not get around that rule when the strength is within 10%. The FDA also says 503B outsourcing facilities may not use semaglutide or tirzepatide as a raw drug ingredient (API), because it is not on the 503B bulks list or a shortage list. As of May 31, 2026, the FDA had 990 reports of side effects or other problems (adverse events) with compounded semaglutide and more than 730 with compounded tirzepatide.

How the mistake happens

A vial label may give mg, a pharmacy may give directions in mL or units, and the syringe may show only units. These numbers are related, but you can’t swap one for another. On a U-100 syringe (100 units fill 1 mL, so 1 unit is 0.01 mL), 5 units is 0.05 mL and 50 units is 0.50 mL. The FDA alert described patients who were told to draw 5 units with a 1 mL syringe and drew 50 units instead.

The alert also described math mistakes by healthcare providers, including 25 units prescribed instead of 5, and 20 units instead of 2. The strength (mg per mL) has to be part of the math: prescribed mg ÷ mg/mL = mL, then mL × 100 = U-100 units. The syringe size should fit the result, because on a big syringe a small amount is harder to judge.

Before you draw, compare four things: your prescribed dose in mg, the vial’s strength, the scale on the syringe (U-100 or another), and how much the syringe holds. If any of these is missing or doesn’t match the others, stop and contact your healthcare provider or pharmacist.

Doses above the label

The FDA has reports of adverse events (health problems reported after taking a drug) linked to compounded semaglutide and tirzepatide prescribed above the label doses. That includes larger amounts, more frequent doses, or stepping up the dose faster. As of May 31, 2026, there were 990 reports for compounded semaglutide and more than 730 for compounded tirzepatide. These are counts of reports. They don’t show how often problems happen, and they don’t mean every report had the same cause.

The FDA also says there is no known legal basis for compounding “salt” versions of semaglutide, such as semaglutide sodium or semaglutide acetate. If your vial label names one of these, ask your pharmacist about it.

A pen mistake: counting clicks

The Ozempic instructions for use say to set the dose with the dose counter, and state plainly, “Do not count the pen clicks.” So this site doesn’t teach counting clicks or turn clicks into mg or units. The pen’s dose counter and its instructions decide how you set the dose.

That warning is separate from vial math. Drawing from a vial uses a given strength and the lines on a syringe. A brand-name pen measures its labeled dose its own way. Don’t apply vial math to a pen, and don’t apply click-counting to a vial or syringe.

Common questions

How big were the overdoses the FDA reported?

The July 26, 2024 alert said that in some reports, patients took five to 20 times more than their intended dose.

When should a compounded multi-dose GLP-1 vial be thrown out?

The FDA advises throwing it out 28 days after first use, even if the compounding label says it lasts longer.

Can I count Ozempic pen clicks?

No. The Ozempic instructions for use say not to count pen clicks. Use the dose counter and follow the product instructions.

Sources

The medical and device facts on this page come from these sources. Each entry shows the date we accessed it.

01 FDA alerts about dosing errors with compounded semaglutide · U.S. Food and Drug Administration, 07/26/2024. Accessed 2026-09-28.
02 FDA's concerns with unapproved GLP-1 drugs used for weight loss · U.S. Food and Drug Administration, 10/01/2026. Accessed 2026-10-01.
03 FDA clarifies policies for compounders as GLP-1 supply stabilizes · U.S. Food and Drug Administration, 04/01/2026. Accessed 2026-09-28.
04 Ozempic (semaglutide) US Prescribing Information · Novo Nordisk, 05/2026. Accessed 2026-09-28.
05 Technical Data Sheet – Insulin Syringes · embecta, Rev B, 12/2025. Accessed 2026-09-28.

Medically reviewed by Ashley Alexis, NDLast reviewed September 30, 2026How we review