What semaglutide is
Semaglutide is the drug in Ozempic and Wegovy. Their labels call it "a human GLP-1 receptor agonist (or GLP-1 analog)" and say its peptide backbone is produced by yeast fermentation. They give its molecular formula as C187H291N45O59 and its molecular weight as 4113.58 g/mol.
The approved injections are ready-made liquids in sealed devices. The Ozempic label lists single-patient-use pens at 0.68 mg/mL, 1.34 mg/mL and 2.68 mg/mL, and single-dose prefilled syringes. The Wegovy label lists single-dose pens, single-dose syringes and a single-patient-use pen at 3.2 mg/mL. Neither label mentions a vial or an insulin syringe, so this calculator has nothing to do with those products.
A vial of semaglutide is something else. FDA says compounders offer semaglutide injectable products "in various containers and packaging, including multiple-dose vials and prefilled syringes", and that concentrations may vary depending on the compounder. That's why this page opens on the liquid setting and asks for the strength on your own vial's label. Neither FDA page this one rests on mentions semaglutide as a powder to mix. The powder setting is here because the calculator has one.
Where it stands with the FDA
Semaglutide is FDA-approved. An FDA alert whose page was current as of July 26, 2024 says there were then three FDA-approved semaglutide products, and names them as Wegovy injection, Ozempic injection and Rybelsus tablet. The Ozempic and Wegovy labels both give the initial U.S. approval as 2017. The Wegovy label on DailyMed in October 2026 covers tablets as well as the injection.
A search of DailyMed, the National Library of Medicine's collection of drug labels, for semaglutide in October 2026 returned 9 labels. None of their titles mentions a vial or a powder.
A compounded vial is not one of the approved products. FDA's page on unapproved GLP-1 drugs, current as of October 1, 2026, says "compounded drugs are not FDA approved. This means the agency does not review compounded drugs for safety, effectiveness or quality before they are marketed." It also says a compounded drug might be appropriate if a patient's medical need cannot be met by an FDA-approved drug, or the FDA-approved drug is not commercially available. Its recommendations put it more firmly, saying "Compounded drugs should only be used in patients whose medical needs cannot be met by an FDA-approved drug."
The same page says some semaglutide products sold by compounders may be salt forms, including semaglutide sodium and semaglutide acetate. FDA calls these "different active ingredients than are used in the approved drugs" and says it is "not aware of any lawful basis for their use in compounding". This calculator can't tell which form is in a vial. It works from the number you type in.
FDA also says it has warned companies that illegally sold unapproved drugs containing semaglutide "falsely labeled" as for research purposes or not for human consumption. It says these products "are of unknown quality and may be harmful" and urges consumers not to purchase them.
As of May 31, 2026, FDA says it had received 990 reports of adverse events associated with compounded semaglutide. It adds that it is not always possible to determine if an adverse event directly resulted from use of the drug, and that adverse events from compounded versions are likely underreported.
What FDA says about dosing errors
FDA has published an alert about the conversion this page does. It says the agency "has received reports of adverse events, some requiring hospitalization, that may be related to overdoses due to dosing errors associated with compounded semaglutide injectable products". The alert's page was current as of July 26, 2024.
FDA says the errors came from patients measuring and self-administering incorrect doses and from health care providers miscalculating doses. It says unfamiliarity with drawing medication from a vial into a syringe, "coupled with confusion between different units of measurement", may have contributed. The units it names are milliliters, milligrams and "units".
The alert says many of the patients who received vials "lacked experience with self-injections", and that most of the reports indicated patients were unfamiliar with how to measure the intended dose using a syringe. It says FDA is aware of some instances in which patients were given syringes "significantly larger than the prescribed volume of semaglutide", and it encourages health care providers and compounders to provide the appropriate syringe size for the intended dose.
The alert says the majority of the reports described patients drawing up more than the prescribed dose from a multiple-dose vial, and that in these instances patients "administered five to 20 times more than the intended dose". In several reports, patients had been told to use a U-100 (1 milliliter) insulin syringe "to draw small doses, such as a 5-unit (0.05 milliliter) dose", and mistakenly administered 50 units instead.
In one reported case, the alert says, a patient found it difficult to get clear dosing instructions from the telemedicine provider, did "an online search for medical advice" and took five times the intended dose. A page like this one is what an online search turns up. It can check arithmetic. It can't tell anyone what their dose is.
The alert covers health care providers' errors too. It says several reports describe health care providers incorrectly calculating the intended dose when converting from milligrams to units or milliliters, which resulted in patients administering "five to 10 times more than the intended dose".
FDA says the instructions that come with a compounded drug, "if provided", may tell users to inject in "units", "the volume of which may vary depending on the concentration", rather than in milligrams or milliliters. It says product concentrations may vary depending on the compounder, and that a single compounder may offer multiple concentrations. It says these factors "may cause confusion" for providers and for patients measuring their own doses. This page's arithmetic shows the same thing from the other side. The same number of units holds a different amount of semaglutide at a different strength.
The adverse events FDA lists from these errors are "gastrointestinal effects (e.g., nausea, vomiting, abdominal pain), fainting, headache, migraine, dehydration, acute pancreatitis and gallstones". It says a prolonged period of observation and treatment for overdose symptoms may be necessary "due to the long half-life of semaglutide of about one week".
FDA "encourages patients to talk with their health care provider or compounder about how to measure and administer the intended dose of compounded semaglutide". This calculator isn't a substitute for that. It shows each answer in syringe units and in mL, with the dose in mcg and mg and the strength it was worked from, so the figures can be checked against what a prescriber or pharmacy wrote down.
What the labels say
The Ozempic and Wegovy labels give doses for their own pens and syringes, and both are once weekly. The Ozempic label, whose indications are all for adults with type 2 diabetes mellitus, says "Start at 0.25 mg once weekly. After 4 weeks, increase the dosage to 0.5 mg once weekly." The Wegovy label says "Initiate at 0.25 mg once weekly for 4 weeks. Then follow the dosage escalation schedule in Table 1, titrating every 4 weeks to achieve the maintenance dosage." Those are the labels' words about the approved devices, for a prescriber to apply. They aren't a suggestion from this page.
FDA's page on unapproved GLP-1 drugs says the agency has received adverse event reports that may be related to patients prescribed compounded semaglutide or tirzepatide "in doses beyond what is in the FDA-approved drug label".
Both labels carry a boxed warning. The Ozempic label says "In rodents, semaglutide causes thyroid C-cell tumors", and that it is unknown whether Ozempic causes them in humans. Both labels say the product is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or with Multiple Endocrine Neoplasia syndrome type 2.
The Ozempic label says "The most common adverse reactions reported in ≥5% of patients treated with OZEMPIC are: nausea, vomiting, diarrhea, abdominal pain and constipation."
On overdose, the Wegovy label says "Overdoses have been reported with other GLP-1 receptor agonists. Effects have included severe nausea, severe vomiting, and severe hypoglycemia." It says to consider contacting the Poison Help line or a medical toxicologist, and that a prolonged period of observation and treatment may be necessary, "taking into account the long half-life of WEGOVY of approximately 1 week".
The Wegovy label also says using Wegovy "with other semaglutide-containing products or with any other GLP-1 receptor agonist is not recommended".
Storing semaglutide
FDA's page on unapproved GLP-1 drugs says "Generally, FDA recommends that vials containing multiple doses of sterile medications be used within 28 days after the first use because there is an increased risk of contamination after 28 days." It recommends discarding the vial within 28 days after the first use even if medication remains, and not using it for longer "even if instructions from the compounder say the medication can be used for longer than 28 days". It also says "Always use a new, sterile needle and syringe for each dose."
The same page says "Injectable GLP-1 drugs require refrigeration as indicated in their package inserts", and that the agency recommends patients not use any injectable GLP-1 drug that arrives warm or with insufficient refrigeration.
The labels' storage instructions are for their own devices. The Ozempic label says that prior to first use the pen should be stored in a refrigerator between 2°C to 8°C (36°F to 46°F), and says "Do not freeze OZEMPIC and do not use OZEMPIC if it has been frozen."
FDA's 28-day recommendation is about vials holding multiple doses in general. Neither FDA page says anything about a vial of semaglutide powder, including how long one keeps once it's mixed.
Semaglutide dosage calculator questions
How do I turn a semaglutide dose into syringe units?
Divide the dose by the concentration to get millilitres, then multiply by 100. A 5 mg vial mixed with 2.5 mL is 2 mg/mL, so one unit on an insulin syringe holds 20 mcg and ten units hold 200 mcg.
How much bacteriostatic water goes in a 5 mg vial of semaglutide?
There's no single right amount. The water only sets the concentration, and the amount of semaglutide in the vial stays the same. With 5 mg, 1 mL makes 5 mg/mL, 2 mL makes 2.5 mg/mL and 3 mL makes 1.667 mg/mL. Choose the amount that puts your dose somewhere between about 10 and 40 units, where it's easiest to read.
What if my semaglutide is already a liquid?
Choose the liquid option and enter the strength printed on the vial, in mg per mL. There's no mixing step, so the volume is the dose divided by that strength, and the units are that volume times 100. At 1 mg/mL, one unit holds 10 mcg and ten units hold 100 mcg. Double the strength and every mark holds double.
Is semaglutide approved by the FDA?
It's FDA-approved, in products that include Ozempic and Wegovy. Their labels list pens, prefilled syringes and, for Wegovy, tablets. A compounded vial of semaglutide isn't FDA-approved. FDA says it doesn't review compounded drugs for safety, effectiveness or quality before they're marketed.
Does this page tell me how much semaglutide to take?
No. The Ozempic and Wegovy labels give doses for their own pens and syringes, and this page reports them as quotes under what the labels say, not as advice. The dose box starts empty, and the chart only converts.
Is a unit on the syringe the same as a milligram of semaglutide?
No. A unit is a volume, a hundredth of a mL on a U-100 insulin syringe. How much semaglutide it holds depends on the strength of the liquid in the vial. FDA's alert on compounded semaglutide says confusion between milliliters, milligrams and units may have contributed to dosing errors.
Can I use this calculator for an Ozempic or Wegovy pen?
No. Those come as pens, prefilled syringes and tablets, not as vials. Their labels don't mention a vial or an insulin syringe, so there's nothing here to convert.
My vial's instructions only give units. Is that enough?
Not to check the sum. FDA says instructions with compounded semaglutide, "if provided", may give the injection in "units", "the volume of which may vary depending on the concentration". To check a number of units you need the strength printed on the vial, in mg per mL, and the dose in mg or mcg. If either is missing, ask the prescriber or the pharmacy that made it.
More peptide calculators by name
The same instrument, set up one peptide at a time. For any other vial, use the peptide reconstitution calculator.