Safety
When compounded concentration changes between refills
Compounded GLP-1 refills can arrive at a different concentration than your previous vial. When that happens, the same number of 'units' now delivers a
Compounded GLP-1 refills can arrive at a different concentration than your previous vial. When that happens, the same number of 'units' now delivers a different dose. Always check the concentration on each new vial and recalculate the volume with your prescriber before injecting.
What you need to know
Different compounding batches or pharmacies can prepare the drug at different strengths. Unlike an approved product with a fixed, labeled concentration, a compounded vial's mg/mL is a property of that batch — and it can change without you changing anything about your prescription.
The hazard is silent: if you keep drawing the same 'units' you drew last time, a higher-concentration refill means an accidental overdose, and a lower-concentration one means under-dosing. Nothing on the syringe warns you; only the concentration figure does.
The habit that prevents this is boringly reliable: treat every new vial as a new product until you've confirmed its concentration, and recompute the volume for your prescribed milligram dose each time.
| Scenario | Old vial | New vial | Result if unchanged |
|---|---|---|---|
| Higher concentration | 2.5 mg/mL | 5 mg/mL | Double the intended dose |
| Lower concentration | 5 mg/mL | 2.5 mg/mL | Half the intended dose |
| Same concentration | 2.5 mg/mL | 2.5 mg/mL | Dose unchanged (verify anyway) |
- Read the concentration (mg/mL) on the new vial
- Compare it to the previous vial
- Recompute the injection volume for your mg dose with your prescriber
- Do not assume continuity
What the evidence shows
- This guidance reflects FDA compounding information, USP standards, and state board of pharmacy resources.
- Verification steps here are public and checkable.
What the evidence does not show
- That following these steps makes a compounded product FDA-approved — it does not.
- That this page replaces personalized medical or pharmacist advice.
Frequently asked questions
Can my compounded dose change without me changing anything?
Yes — if the refill's concentration differs, the same units deliver a different dose.
How do I stay safe across refills?
Check mg/mL every time and recompute the volume for your mg dose.
Related: pharmacy verification hub · safety hub · cost calculator. Compounded medications are not FDA approved.
Not medical advice. This page is consumer education, not medical advice, and does not recommend a dose, product, or provider. Compounded medications are not FDA approved. Talk with a licensed clinician about your situation.