Peptide Calculator: The Number Is Right. The Vial Is Wrong.
A man sits at a kitchen table with a vial of white powder, a syringe, and a browser tab open on a peptide calculator, and he types in the numbers the label gave him. The tool returns a volume to the hundredth of a milliliter, and that precision is the part he trusts. He can trust the division. He cannot trust the label, the vial, or the chain of arithmetic that led to either.
Here is the direct answer to the question that brought most readers here. A peptide calculator does division, division is the only part of this that works, and no calculator can know what is inside the vial it is doing arithmetic about.
The FDA has spent two years documenting that gap. As of May 31, 2026, the agency had logged 990 reports of adverse events associated with compounded semaglutide and more than 730 associated with compounded tirzepatide, and its own alert describes patients who took five to 20 times the intended dose drawn from a multiple-dose vial. The arithmetic on those syringes was performed correctly. The number going into it had changed meaning on the way.
The tool is not the danger. The tool is the alibi.
FDA – a peptide calculator cannot verify the number you feed it
On July 26, 2024, the FDA published a safety alert whose title reads like a case file: FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products.
The findings are specific. Most reports described patients drawing more than the prescribed amount from a multiple-dose vial, and in those instances patients “administered five to 20 times more than the intended dose of semaglutide.” Prescribers converting milligrams into units or milliliters did the rest:
- A provider meant to write 0.25 milligrams, which was 5 units, and wrote 25. The patient got five times the intended dose and severe vomiting.
- Another wrote 20 units instead of 2. Three patients received 10 times the dose, with nausea and vomiting.
- A patient who was himself a health care provider recalculated his own dose in units and gave himself 10 times the intended amount.
One case reads like the moment a calculator tab gets opened. The patient could not get clarity on instructions from the telemedicine provider who wrote the prescription, searched online for medical advice, and took five times the intended dose.
The FDA also explained why the number changes between the label and the syringe. Compounded semaglutide arrives in multiple-dose vials at concentrations that vary by compounder, and instructions may arrive written in “units,” a unit of volume whose size depends on the concentration. Patients told to draw 5 units with a U-100 (1 milliliter) insulin syringe drew 50.
No one in that alert fumbled the multiplication. A number that had changed meaning got handed out.
Bernard Gramlich – the FDA named the water that goes into the vial
The second document is a warning letter dated March 31, 2026, reference 721806, addressed to Bernard Gramlich of Gram Peptides in Rancho Santa Fe, California.
The FDA reviewed grampeptides.com from January to March 2026 and found the site offering “Retatrutide,” which the firm called “GLP-1-R peptide,” “Tirzepatide,” which the firm called “GLP-2 peptide,” and “Bacteriostatic Water for Injection.”
The site carried the standard shield: “Research Use Only,” and “not intended for human consumption, medical use, or veterinary use.” The FDA quoted the sales copy back at it, including a claim that the peptide “influences appetite suppression, insulin sensitivity, thermogenesis, and fat-oxidation models,” and concluded the language shows the products are intended as drugs for human use.
Then comes the paragraph that matters to anyone holding a reconstitution calculator. The firm offers bacteriostatic water “alongside peptide products, which are drugs intended for injection and require reconstitution,” the letter says, and “the sale of these products together demonstrates that you intend for your ‘Bacteriostatic Water for Injection’ to be used in combination for injection. Therefore, your ‘Bacteriostatic Water for Injection’ is a drug.”
The letter lists the retatrutide, the tirzepatide and the water as unapproved new drugs and gives 15 working days to respond. A companion letter went to Prime Sciences the same day over cagrilintide, “GLP1-R (10MG),” mazdutide and “BAC water.”
The milligram figure sits in those product titles. The water that turns the powder into a liquid sits in the same shopping cart. The vial was not the whole purchase.
The 53-year-old man – 2 mg instead of 0.1 mg
Wiener and colleagues published in Clinical Toxicology in February 2024 three unintentional semaglutide overdoses at initiation. A 53-year-old man injected 2 milligrams instead of the intended 0.1. A 45-year-old woman injected 2.4 instead of 0.25. A 33-year-old woman injected 1.7. All three developed gastrointestinal symptoms, and none developed hypoglycemia, which is worth naming, because the fear most people carry about an overdose of this drug is the wrong fear. The authors attributed the overdoses to “deficits in patient and prescriber knowledge, and evasion of regulated access to pharmaceuticals.”
Earlier, Lambson and colleagues reported in the Journal of the American Pharmacists Association in 2023 three cases that reached a regional poison control center after compounded semaglutide came from compounding pharmacies and an aesthetic spa. Two patients self-administered 10-fold errors. One received a vial with syringes and no pharmacist counseling. One described dosing “in milliliters and units rather than in milligrams.”
The failure in each paper is a failure to know how much drug sits in the liquid being measured.
The 503A list – a peptide calculator for a compound the law has not placed
On July 23 and 24, 2026, the FDA’s Pharmacy Compounding Advisory Committee met to consider seven peptide bulk drug substances for the 503A bulks list: BPC-157, KPV, TB-500, MOTS-c, Emideltide (DSIP), Semax, and Epitalon, each in free base and acetate forms. Committee advice is non-binding. The regulation itself, 21 CFR 216.23, checked on October 7, 2026, lists six substances that can be used in compounding, and not one of them is a peptide from that meeting.
That regulation states that inadequate data exist to demonstrate the safety or efficacy of any drug compounded with a listed bulk substance, and that representing such a drug as FDA approved causes misbranding.
For the GLP-1 side of the same question, the FDA’s consumer page is blunt: retatrutide and cagrilintide “cannot be used in compounding under federal law,” they are not components of FDA-approved drugs, and they “have not been found safe and effective for any condition.” The agency has warned companies that sold semaglutide, tirzepatide, retatrutide, survodutide or mazdutide labeled “for research purposes” or “not for human consumption” while selling to consumers “with dosing instructions.”
Beside a reconstitution calculator, that leaves the tool one job: convert a labeled mass into a draw volume, when the labeled mass is the one number no independent lab has confirmed. A tidy number for a compound with no established dose is a tidy number and no information.
The dose that went wrong with no calculator and no vial
The newest case in this pile involves no compounded vial and no browser tab. In a 2026 case report, a 50-year-old man with obesity had taken semaglutide at 2.4 milligrams weekly for more than eight months, tolerated it well, and had gone from 106 kilograms to 94. On the first injection from a new pen he saw liquid still in the cartridge, read that as a failed injection, and repeated doses until the pen was empty. The authors estimate the total at 9.6 milligrams, four times the intended weekly dose, from an FDA-approved device set to the correct dose.
Two days later he had generalized burning dysesthesia and marked weakness, with no nausea and no abdominal pain. Symptoms resolved within seven days.
He used a pen that sets the dose for him, and his reading of what he saw still quadrupled his exposure.
The dose was set correctly. His belief about the dose was not.
What a peptide calculator cannot tell you, and who can
The FDA’s stated position is narrow: compounded drugs should be used only in patients whose medical needs cannot be met by an FDA-approved drug, and patients should get a prescription from a doctor and fill it at a state-licensed pharmacy.
The questions worth asking before any needle goes in: who wrote the prescription, which licensed pharmacy compounded the product, what concentration is printed on the label in milligrams per milliliter, what the instruction says in milligrams, whether the product is a salt form such as semaglutide sodium or semaglutide acetate, and whether the seller will name a licensed prescriber. The FDA calls those salt forms different active ingredients and says it knows of no lawful basis for their use in compounding.
One honest limit. The FDA cannot determine with certainty whether a reported adverse event came from the drug or from other factors, and federal law does not require state-licensed pharmacies that are not outsourcing facilities to report at all. Those 1,720 reports are a floor.
The tool answers a question about volume. The question that decides your week is about content.
Frequently asked questions
Is a peptide calculator accurate?
Its arithmetic is. The answer is only as good as the concentration you typed in, and a vial bought outside a licensed pharmacy carries no verified concentration.
Why do these overdoses run five to 20 times the intended dose?
The instruction arrives in units and the syringe measures in milliliters, or a prescriber converts milligrams to units incorrectly. The FDA documented patients told to draw 5 units who drew 50.
Can a peptide calculator replace instructions from a prescriber or pharmacist?
No. A web page cannot know your product, your concentration or your history, or whether a vial holds what its label claims.
What is bacteriostatic water for injection, and why did the FDA warn about it?
It is water with a preservative, used to turn a powder into an injectable liquid. In the March 31, 2026 warning letters to Gram Peptides and Prime Sciences, the FDA concluded that bacteriostatic water sold alongside peptides intended for reconstitution is itself a drug.
Is retatrutide legal to compound in the United States?
No, as the FDA states it. Retatrutide and cagrilintide cannot be used in compounding under federal law and are not components of any FDA-approved drug. Our peptide tracker follows the seven peptides the advisory committee reviewed.
Are compounded GLP-1 products FDA-approved?
No. The FDA states compounded drugs are not FDA-approved, are not reviewed for safety, effectiveness or quality before marketing, and are not the same as generics, which are FDA-approved.
Two disclosures belong on the record. The figures quoted here describe brand-name, FDA-approved products; compounded versions are not FDA-approved and were not the drugs studied in those trials. Nothing on this page is a dosing instruction, which is why the FDA’s error examples appear as errors.
Sources: U.S. Food and Drug Administration, dosing errors with compounded injectable semaglutide products, July 26, 2024, FDA warning letter 721806 to Gram Peptides, March 31, 2026, FDA warning letter 721805 to Prime Sciences, March 31, 2026, FDA, concerns with unapproved GLP-1 drugs used for weight loss, FDA press release, 30 warning letters to telehealth companies, Wiener et al., Clinical Toxicology, February 2024, Lambson et al., Journal of the American Pharmacists Association, 2023, Quarenghi et al., case report, 2026, 21 CFR 216.23, eCFR, FDA Pharmacy Compounding Advisory Committee, July 23-24, 2026.
The same question sits behind every reconstitution video, and the federal record answers it the same way: what FDA published about the substances sold for reconstitution, and why none of it is a recipe.
Update, 20 October 2026: FDA has now cited a peptide calculator as evidence of intended human use in warning letters dated 24 August 2026. We walked through those letters in Peptides for Research: FDA Named Nine of Them Drugs.