Compounded GLP-1 medicines are sometimes dispensed in multi-dose vials that you draw from with a syringe — a different process than a branded, pre-filled pen. When milligrams (mg), milliliters (mL), and syringe “units” get mixed up, people can accidentally take far more medicine than intended. The FDA has publicly warned patients, providers, and compounders about exactly these dosing errors. This page explains the label language; it does not replace a teach-back with your pharmacy.
mg, mL, and “units” are three different things
- mg (milligrams) is the amount of drug — usually how your prescription is written.
- mL (milliliters) is the volume of liquid you draw. Two vials labeled the same can have very different mg per mL, so the same mL can mean very different amounts of drug.
- “Units” on an insulin-style syringe are just hash marks — not a universal dose. They only mean something once your pharmacy tells you how many markings equal your prescribed mg for that specific vial concentration.
Never assume “10 units,” “0.5 mL,” and “2.5 mg” are interchangeable. They are related only through the concentration printed on your specific vial and the syringe your pharmacy told you to use. Copying a friend's dose, a social-media chart, or an old vial's instructions can be dangerous, because those may assume a different concentration.
How people have drawn several times the intended dose
- Confusing mg on the prescription with mL or syringe units.
- Using a dosing chart that assumed a different concentration than the vial in hand.
- Treating “units” on an insulin syringe as if they were milligrams of the drug.
- Drawing to a convenient line (a full half-mL, or “10 units”) without checking the conversion for that vial.
- Reusing old instructions after the pharmacy changed the concentration or syringe type.
What to confirm before your first injection
- Read the pharmacy label and vial label together — drug, concentration (mg/mL), beyond-use date, storage, and prescribed dose.
- Confirm the concentration with the pharmacy or your provider if anything is unclear or different from what you expected.
- Ask for a teach-back: have someone walk through how your mg dose converts to the volume or markings you'll use.
- Use only the syringe type your pharmacy specified — don't substitute a different scale.
- Write the plan in plain words (“My dose is X mg. For this vial, that's Y mL / Z markings”) and keep it with the vial.
- Don't “eyeball” the dose or round up “just to be sure.” If you can't explain your dose in your own words, don't inject — call the pharmacy first.
When to seek urgent care
After a larger-than-intended dose, people may have severe or lasting nausea, vomiting, abdominal pain, dizziness, or signs of dehydration. Seek urgent or emergency care for persistent vomiting you can't keep fluids down against, severe abdominal pain, fainting, chest pain or trouble breathing, severe allergic symptoms, or confusion — and bring the vial, syringe, and label. In the U.S. you can also call Poison Control at 1-800-222-1222; call 911 for life-threatening emergencies.
Education only — not medical advice, and not a dosing guide. Compounded medicines are not FDA-approved. Follow your own prescription, the concentration on your own vial, and your licensed pharmacist and clinician. New Start MD services are for adults 18+.
Sources
The primary sources behind this article — so you can read them yourself.
- FDA — Dosing errors associated with compounded semaglutide — U.S. Food and Drug Administration
- FDA — Human drug compounding (overview) — U.S. Food and Drug Administration
- GLP-1 agonists — patient overview — MedlinePlus
- Poison Control (U.S.) — 1-800-222-1222 — America's Poison Centers
Products are available only by prescription after a consultation with a licensed provider, who decides whether treatment is appropriate. Many compounds described here are not FDA-approved medicines and have not been tested in people for the uses described; information on this site is educational and is not medical advice.