Your dose is a milligram (mg) amount of medicine. How much liquid that takes, in milliliters (mL), depends on how concentrated your vial is. And “units” on an insulin syringe are not a drug amount at all: they are a measure of volume, where 100 units fill 1 mL. Mixing these up is the most common way people get a compounded GLP-1 dose wrong, and the FDA has documented patients injecting five to 20 times the dose they were prescribed.
The safe rule is short: follow your pharmacy label, never convert a dose yourself, and ask before you draw if anything does not match. Here is what each number means and what to check.
Three numbers, three meanings
Milligrams (mg): the dose. This is how much medicine you take. Doctors prescribe, and labels state, GLP-1 doses in mg: a weekly injection might be 0.25 mg of semaglutide or 2.5 mg of tirzepatide.
Milliliters (mL): the volume. This is how much liquid contains that dose. It depends on the concentration, written as mg per mL. The same mg dose is a different volume in a vial of a different strength, even for brand-name medicines: Zepbound’s 2.5 mg dose is 0.5 mL in its single-dose vial but 0.6 mL from its multi-dose vial, which holds 4.17 mg in every mL (Zepbound prescribing information).
Units: markings on the syringe. A standard U-100 insulin syringe is marked so that 100 units equal 1 mL; “every small notch on a standard 1 mL insulin syringe is 1 unit” (MedlinePlus). So 10 units is 0.1 mL, whatever is in the syringe. How many mg that is depends entirely on the vial’s concentration, and compounded concentrations differ from pharmacy to pharmacy.
What the FDA has seen go wrong
In 2024 the FDA alerted patients and providers to dosing errors with compounded semaglutide injections. Its findings (FDA alert):
- Most reports were patients drawing up more than their prescribed dose from a multiple-dose vial, and taking “five to 20 times more than the intended dose.”
- Patients told to draw 5 units (0.05 mL) with a 1 mL syringe drew 50 units instead.
- Some providers converted mg into units or mL incorrectly, so patients took five to 10 times the intended dose.
- Some patients were given syringes much larger than the volume they needed.
- People reported nausea, vomiting, abdominal pain, fainting, headache, migraine, dehydration, acute pancreatitis and gallstones, and some needed hospital care.
The FDA’s current page on unapproved GLP-1s adds reports involving compounded semaglutide or tirzepatide “in doses beyond what is in the FDA-approved drug label,” whether a larger dose, more frequent doses, or faster increases. As of May 31, 2026, it had received 990 adverse event reports for compounded semaglutide and more than 730 for compounded tirzepatide, and it notes these are likely underreported (FDA).
What your label and supplies should tell you
Before your first dose, check that you can find all of these:
- The medicine and its concentration, in mg per mL.
- Your dose in mg, matching what your doctor told you.
- How much to draw, in mL or in units, for that dose.
- A syringe sized for the dose. A small dose in a large syringe is hard to measure accurately.
- How often, and when the dose is due to change.
If you can find them, the three should agree: the volume you draw, times the concentration, should equal your mg dose. If they do not agree, or anything is missing, or the vial looks different from your last one, stop and message your prescriber before drawing a dose. Do not use a conversion chart from the internet or a dose from another patient. Your vial’s concentration is what decides the volume.
Habits that prevent errors
- Use the dose on your current label. A new vial can be a new concentration, so the same mg dose can mean a different number of units.
- Do not raise your own dose. Dose increases are your doctor’s decision, no faster than every four weeks on the brand-name schedules.
- One needle and syringe per dose. The FDA advises a new, sterile needle and syringe every time, and discarding a multiple-dose vial 28 days after first use, even if medicine remains.
- Do not use an injection that arrives warm. The FDA recommends against using any injectable GLP-1 that arrives warm or without enough refrigeration.
- Know the overdose signs. Severe nausea, repeated vomiting, severe abdominal pain or fainting after a dose need medical attention; call 911 for trouble breathing or symptoms that seem life-threatening.
Two products to avoid outright
Salt forms. Some products are made with semaglutide sodium or semaglutide acetate. The FDA says these “are different active ingredients than are used in the approved drugs” and that it is “not aware of any lawful basis for their use in compounding.” Ask which form your pharmacy uses.
“Research use” products. The FDA has warned companies that sold semaglutide and tirzepatide labeled “for research purposes” or “not for human consumption” directly to consumers with dosing instructions, and it urges consumers not to buy them. They are not prescriptions, there is no pharmacist checking the dose, and the contents are unknown. Buy only from state-licensed pharmacies, through a prescription.
How we handle it
Gentle Health prescribes compounded semaglutide and tirzepatide as weekly injections, and your doctor sets your dose in mg. A state-licensed US pharmacy compounding under Section 503A prepares it for your individual prescription; ask us and we will send the pharmacy’s license or lab results. Every injectable order ships with the supplies you need to take it. Milligrams of medicine and the syringe’s volume markings are not interchangeable: the volume depends on the concentration on your own vial’s label. If a label, vial, syringe or dose does not match what you expected, message your doctor before you take it: that is part of the care included in the price. Our doctor also prescribes brand-name Zepbound, Wegovy and Foundayo, which you buy through LillyDirect or NovoCare and receive with the maker’s instructions for use.
Compounded medications are not FDA-approved. More on how compounding pharmacies work is in what 503A and 503B pharmacies are, and on choosing a provider in how to verify an online semaglutide provider.
Frequently asked questions
How many units is 0.25 mg of semaglutide? It depends on your vial’s concentration, which is why there is no single answer. Units measure volume on a U-100 syringe (100 units = 1 mL), so the same mg dose is a different number of units in vials of different strengths. Use the volume on your pharmacy label, and ask your prescriber if it is not there.
Are units the same as milligrams? No. Milligrams are the amount of medicine; units are syringe markings for volume. Confusing the two is how the FDA’s documented overdoses happened.
What should I do if I took too much? Contact your prescriber or Poison Control (1-800-222-1222) straight away, and get emergency care for severe vomiting, severe abdominal pain, fainting or trouble breathing. The FDA notes that semaglutide stays in the body for about a week, so symptoms can last.
Is compounded semaglutide sodium safe? The FDA says salt forms such as semaglutide sodium and acetate are different active ingredients from the approved drugs, and it is not aware of any lawful basis for compounding with them. Ask your pharmacy which form it uses.
Can I reuse a syringe? No. The FDA advises a new, sterile needle and syringe for every dose.
Dr. James Simmons, MD