A compounded GLP-1 arrives as a small glass vial of clear liquid, and almost nothing about it is printed the way a pharmacy box is. The molecule may not be in the same chemical form the trials used. The strength is a concentration rather than a dose. And in a growing number of preparations there is more than one active ingredient in there. None of that is the approval question handled in the compounding article; this is a question about contents.
Base form and salt form are not the same ingredient
The approved products contain the base form of semaglutide. The Wegovy label describes a peptide backbone produced by yeast fermentation, gives the molecular formula as C187H291N45O59, and puts the molecular weight at 4,113.58 g/mol. That is one specific substance with one specific identity.
The FDA has said that some semaglutide sold by compounders may instead be a salt form, naming semaglutide sodium and semaglutide acetate, and that these are different active ingredients from the one used in the approved drugs.[1] The agency added that it does not have information on whether the salts share the chemical and pharmacologic properties of the approved ingredient, and that it is not aware of a lawful basis for using them in compounding.[1]
That is a narrower statement than “the salts do not work,” and it should be read narrowly. The honest position is that a buyer holding a salt-form vial is holding something whose equivalence nobody has established. How many sellers dispense one is not published anywhere, so the practical move is to ask which form the pharmacy uses and treat a non-answer as the answer.
The vial is a concentration, not a dose
An approved pen removes arithmetic from the transaction. Each Wegovy single-dose pen contains one amount of semaglutide, so a 1.7 mg pen delivers 1.7 mg and there is nothing to work out. A compounded vial is sold at a concentration in milligrams per milliliter, and the weekly dose is a volume drawn from it.
The FDA has warned about exactly that gap. Its alert names the risk of dosing errors arising from converting milligrams into other units of measurement, from compounded semaglutide being available in varying concentrations, and from the use of multiple-dose vials.[2] The reported consequences of an overdose included vomiting, abdominal pain, fainting, dehydration, acute pancreatitis and gallstones.[2]
So the concentration is the number that makes a price and a dose mean anything at all. Two vials priced identically can hold different amounts of drug, and the rungs those amounts correspond to are laid out in the semaglutide dose article and its tirzepatide counterpart.
A multiple-dose vial holds more than the drug
Every injectable carries inactive ingredients. Wegovy’s single-dose presentations list disodium phosphate dihydrate, sodium chloride and water for injection, with hydrochloric acid or sodium hydroxide to adjust pH. Nothing is preserved, because the pen is used once.
The multiple-dose presentation of the same product is different. Its formulation adds phenol and propylene glycol, because a container punctured four times over a month has to resist contamination between uses. A compounded vial is a multiple-dose container by design, so it needs the same kind of protection. Which agent a given pharmacy uses is rarely published, and anyone with a sensitivity has a reason to ask.
The B12, NAD and carnitine combinations
Several sellers do not stop at the peptide. The FDA has recorded that some compounders incorporate additional ingredients into their semaglutide products, naming cyanocobalamin (vitamin B-12), pyridoxine (vitamin B-6), levocarnitine (L-carnitine) and nicotinamide adenine dinucleotide (NAD).[2] These are usually marketed as an upgrade, sometimes as an energy or metabolism addition, and sometimes at a higher price than the plain preparation.
The agency’s sentence on that is one line long and worth quoting exactly: the safety and effectiveness of combining semaglutide with other ingredients has not been established.[2] That is not a warning about vitamin B-12, which is an ordinary and well-characterized substance. It is a statement about the combination, which is a different product from either of its parts.
Why a combination has no trial behind it
The evidence for a GLP-1 comes from trials that gave one molecule at a known dose and compared it against placebo. Adding a second active ingredient creates a preparation that no such trial studied. The result still describes the GLP-1, and it has nothing to say about the mixture in the vial, in either direction.
There is no reason in principle why a combination could not be studied. None has been, for these combinations, and a seller implying that the familiar weight-loss figures apply to a B-12 or NAD blend is extending a result past the thing it measured. Where the ordering of a board is decided, and on what, is set out in the methodology page.
What the reporting data shows, and what it cannot
As of May 31, 2026 the FDA had received 990 reports of adverse events associated with compounded semaglutide and more than 730 associated with compounded tirzepatide.[3] The agency notes that federal law does not require state-licensed pharmacies outside the outsourcing facility category to submit adverse events, so the real count is likely higher.[3]
A published analysis of the same reporting system found 707 compounded product reports among 81,078 GLP-1 reports between 2018 and 2024. Compounded products carried higher reporting odds ratios for preparation errors, at 48.92 (95% CI 12.63 to 189.6), for contamination, at 19.00 (4.24 to 85.03), and for hospitalization, at 2.35 (1.94 to 2.83).[4]
Those numbers describe reporting patterns rather than rates, and the authors state that the design cannot establish cause and effect. Read them as a signal about where the failure modes of a compounded product sit — preparation, contents, contamination — rather than as a measured risk.
Four questions worth asking before the first vial
Which form of the molecule is in it, base or salt? What is the concentration, in milligrams per milliliter? Is anything else in the vial, and if so what and how much? And which pharmacy prepared it?
Sellers differ sharply in how much of that they will put in writing, and the difference is a usable signal on its own. What each company publishes is recorded in the individual seller write-ups, and the figures attached to named strengths sit on the semaglutide board and the tirzepatide board. A price is only a comparable number once you know what the vial holds.