Two words decide this whole argument, and almost everybody uses the wrong one. When the FDA said that semaglutide sodium and semaglutide acetate should not be used to compound semaglutide, it did not say they were a different active moiety. It said they were different active ingredients.[1] Those terms are both defined in federal regulation, they do not mean the same thing, and only one of them is capable of shutting the door the compounding statute opens. Getting this right is what separates a real objection from a slogan, and it also explains why the usual rebuttal — the counterion falls off in solution, so the patient gets the same drug — misses the target entirely. What the law regulates is the powder that went into the vial, not the ion that comes out of the syringe. The container question itself belongs to the article on vial contents.
What the approved products actually contain
Start with the reference point, because the salt argument is only meaningful against a fixed thing. The Wegovy label describes a peptide backbone produced by yeast fermentation, modified at position 26 with a hydrophilic spacer and a C18 fatty di-acid, at position 8 for resistance to DPP-4, and at position 34 so only one di-acid attaches. It gives the molecular formula as C187H291N45O59 and the molecular weight as 4,113.58 g/mol.[2] No salt appears anywhere in that description.
The habit of specifying the free base is not unique to semaglutide. The Victoza label states that each prefilled pen holds a solution “equivalent to 18 mg liraglutide (free-base, anhydrous)”[3] — a phrase that exists precisely because milligrams of a peptide and milligrams of a peptide salt are not the same quantity of drug. A counterion has mass. Label an amount as the salt and some fraction of those milligrams is sodium or acetate rather than peptide, which is a quiet arithmetic problem when the vial is sold as a concentration and the dose is a volume you draw yourself. If you are weighing what a milligram is buying you across sellers, the ordering on the semaglutide board only means something once that quantity is unambiguous.
Moiety and ingredient are different words for a reason
Under 21 CFR 314.3, the active moiety is “the molecule or ion, excluding those appended portions of the molecule that cause the drug to be an ester, salt (including a salt with hydrogen or coordination bonds), or other noncovalent derivative… responsible for the physiological or pharmacological action of the drug substance.”[4] The salt-forming part is excluded by definition. So semaglutide sodium and semaglutide base share an active moiety, and anyone claiming otherwise is contradicting the regulation they are appealing to.
The same section defines an active ingredient as any component intended to furnish pharmacological activity or other direct effect.[4] That is a description of a component: a physical substance a manufacturer puts in, identified by name. Semaglutide sodium is a different component from semaglutide, in the same way that a different bag of powder is a different bag of powder, whatever happens to it later in water. And it is components, not moieties, that the compounding statute is written around.
The three doors, and which one a powder has to walk through
Section 503A exempts a compounded drug from the approval, labeling and track-and-trace requirements that apply to everything else in a pharmacy, but only if a list of conditions is met. One of them governs the raw substance. A pharmacist may compound using a bulk drug substance that either complies with an applicable United States Pharmacopeia or National Formulary monograph, if a monograph exists; or, if no monograph exists, is a component of a drug approved by the Secretary; or, if neither, appears on a list FDA develops by regulation.[5] The same provision adds two further conditions that are easy to skim past: the substance must be made by an FDA-registered establishment, and it must arrive accompanied by a valid certificate of analysis.[5] What that certificate is and is not is covered in the certificate article.
Three doors, and a substance needs exactly one. Take them in the order that can actually be checked.
The third is a published regulation, so it takes a minute to settle. 21 CFR 216.23(a) is the section 503A bulks list in its entirety, and it contains six substances: Brilliant Blue G, cantharidin for topical use, diphenylcyclopropenone for topical use, N-acetyl-D-glucosamine for topical use, squaric acid dibutyl ester for topical use, and thymol iodide.[6] There is no peptide on it, and the regulation adds that there are inadequate data to demonstrate the safety or efficacy of a product compounded with any substance on the list even so.[6] The 503B category has its own separate and equally short list, which the outsourcing-facility article goes through.
The second door is the one FDA tells compounders how to check. Its January 2025 interim policy guidance instructs anyone wanting to know whether a bulk substance is a component of an approved drug product to look it up in the Orange Book.[7] That query is public and it takes seconds. Every approved application with semaglutide as an active ingredient names the ingredient as semaglutide: six applications across Ozempic, Rybelsus, Wegovy and one abbreviated application. A search for semaglutide sodium as an approved active ingredient returns nothing. So does a search for semaglutide acetate.
The first door is the one that cannot be settled from outside. Whether a USP or NF monograph exists for semaglutide, in any form, is a question about a subscription compendium; USP’s site refused every request made for this article. That gap is real and it points in only one direction worth noting: if a monograph existed and a salt met it, the salt would qualify on its own terms. FDA’s position suggests the agency does not believe that is the situation, but the honest statement is that this page could not verify it either way.
What FDA actually said, in full
The agency’s sentence is short and it is worth not paraphrasing. FDA is aware that some semaglutide products sold by compounders may be salt forms; these salt forms, including semaglutide sodium and semaglutide acetate, are different active ingredients than are used in the approved drugs; the agency does not have information on whether these salts have the same chemical and pharmacologic properties as the active ingredient in the approved drug; and it is not aware of any lawful basis for their use in compounding.[1]
Read it as three separate claims, because they are not equally strong. The first is a legal classification and it is firm. The second is an explicit statement of ignorance — not a finding that the salts are inferior, and it should never be quoted as one. The third follows from the first rather than the second: with no approved component and no listing, there is no condition left for the substance to satisfy.
Why the salt appears at all
Salts are ordinary pharmaceutical chemistry. They are made because a salt can be easier to crystallize, easier to purify, more stable as a dry solid, and cheaper to handle than a free base. An API broker selling peptide powder into the compounding market has every commercial reason to supply the form that ships well, and the buyer downstream may not be the party that chose it. FDA has told compounders in plain terms to know their bulk substance suppliers, know what testing those suppliers perform, and confirm the API is sourced from an FDA-registered facility with a valid certificate of analysis.[8] The agency has also placed API repackagers on import alert and recalled bulk material that turned out to be a different substance entirely from the one on the label.[8]
There is published evidence that what reaches the finished vial varies. An analysis of follow-on and compounded semaglutide and liraglutide found impurity profiles distinct from the originators — amino acid deletions and additions, plus unidentified impurities — and significant disparity in strength, impurity sum and high-molecular-weight protein content between compounded semaglutide and originator product on light exposure.[9] A separate analysis of compounded tirzepatide combined with vitamin B12 identified a previously unidentified impurity formed by a reaction between the peptide and certain B12 analogs.[10] Both studies were run by the companies whose products are being copied — the first by Novo Nordisk employees and shareholders, the second by Eli Lilly — which is a real conflict and also, at present, the reason the data exists at all. Nobody else has published comparable characterization. What those impurities have to do with the immune system is the subject of the antibody article.
What a buyer can and cannot tell from a seller’s page
Almost nothing, is the short answer, and the reason is structural rather than sinister. A compounded preparation has no approved labeling, so there is no required field anywhere that says which form of the molecule is in it. A secret-shopper study of 75 weight-loss clinics and medical spas in two states found 42 of them (56.0%) offering compounded GLP-1 products combined with B vitamins, and identified 23 supplying compounding facilities, 4 of 21 assessable ones not licensed to perform sterile compounding at all.[11] A market that varies that much on licensure is not going to be uniform on chemistry.
So the usable signals are indirect. A seller that names its pharmacy, will say in writing which form of the substance it dispenses, and will send you the certificate of analysis for the lot is telling you something real. A seller that answers the form question with a reassurance about quality is also telling you something. FDA’s own list of telehealth warning signs starts with a company claiming the compounded drug is the same as an FDA-approved drug[1] — a claim that is false on the approval question regardless of which powder was used, and doubly so if the powder was a salt. The practical sequence for putting those questions to a pharmacy is in the vetting article.
One last thing to keep straight. None of this establishes that a salt-form vial is dangerous, and this page is not saying that. It establishes that it is unlicensed territory: a substance with no approved component behind it, no listing, no published equivalence data, and a regulator on record saying it cannot find a lawful basis for the use. That is a different complaint from a safety finding, and it is the one the evidence actually supports.