Evidence review
Compounded Is Not the Trial Drug
A trial tests one defined article: a molecule, a form, a concentration, a container. Compounding changes some of those, and the evidence travels only that far.
What a trial actually tested
When STEP 1 reported a mean weight change of −14.9% against −2.4% over 68 weeks, the thing that produced that number was not "semaglutide" in the abstract1.
It was a specific article: a defined molecule in a defined form, at a defined concentration, with defined excipients, in a defined container, made by a defined process, shipped under defined conditions, and administered on a defined titration schedule.
Change any of those and the trial result becomes an argument by analogy rather than a measurement. Sometimes a good analogy. Never the same claim.
FDA's framing, in its own words
The agency is unusually direct on this point. Compounded drugs are not FDA-approved, which means FDA does not verify the safety, effectiveness or quality of compounded drugs before they are marketed2.
It also states the reason the distinction is not academic: poor compounding practices can result in serious drug quality problems, such as contamination or a drug that contains too much or too little active ingredient2.
And it sets the condition under which compounding is appropriate at all — compounded drugs should only be used in patients whose medical needs cannot be met by an FDA-approved drug2.
The salt-form problem
This is the cleanest example of "not the same article", and it is worth understanding in detail.
FDA has stated that some semaglutide products sold by compounders may be salt forms, that semaglutide sodium and semaglutide acetate are different active ingredients than those used in the approved drugs, that the agency does not have information on whether these salts have the same chemical and pharmacologic properties as the approved active ingredient, and that it is not aware of any lawful basis for their use in compounding3.
Read that against STEP 1 and the gap is obvious. The trial studied one active ingredient. A salt of that ingredient is a different active ingredient whose properties FDA says it does not have information about. The trial's number does not attach to it, and no amount of confidence in the trial changes that.
What an approved label controls
Identity and strength, verified before marketing.
Impurity limits, with specifications the manufacturer must meet.
Sterility and endotoxin standards for an injectable.
Container closure and stability, which is why the label carries storage instructions at all.
A manufacturing process inspected against current good manufacturing practice.
A named responsible party and a mandatory adverse-event pathway.
Compounding is a different regulatory scheme with different obligations, and which obligations apply depends on whether the compounder is a 503A pharmacy or a 503B outsourcing facility.
Storage is part of the article too
FDA has noted that injectable GLP-1 drugs require refrigeration as indicated in their package inserts, that it has received complaints of certain compounded GLP-1 drugs arriving warm or with inadequate ice packs, and that patients should not use an injectable GLP-1 drug that arrives warm or with insufficient refrigeration because this can affect quality3.
A peptide that has been through an uncontrolled temperature excursion is not the molecule the trial administered, even if it started as the same molecule.
Dosing errors are a design consequence
FDA reports receiving multiple adverse-event reports, some requiring hospitalisation, that may relate to dosing errors with compounded injectable semaglutide — errors arising from patients measuring and self-administering incorrect doses, and in some cases from health care professionals miscalculating doses. It also reports adverse events that may relate to patients being prescribed doses beyond what is in the approved label, whether by using more product in a single dose, dosing more frequently, or escalating faster3.
The mechanism there is not carelessness. An approved product arrives in a device that delivers a fixed increment. A vial and a syringe move that arithmetic to the kitchen table. This site publishes a reconstitution calculator precisely because that arithmetic is error-prone — and it outputs arithmetic, never a dose anyone should take.
What has actually been reported
FDA states that as of 31 May 2026 it had received 990 reports of adverse events associated with compounded semaglutide and more than 730 associated with compounded tirzepatide. It also notes that federal law does not require state-licensed pharmacies that are not outsourcing facilities to submit adverse events to FDA, so these are likely underreported, and that many of the reported events appear consistent with those seen for the approved versions3.
A pharmacovigilance analysis of the same database put structure on it. Of 81,078 GLP-1 receptor agonist reports in FAERS between 2018 and 2024, 707 involved compounded products. Compounded formulations showed higher reporting odds ratios for preparation errors (48.92, 95% CI 12.63 to 189.6), contamination (19.00, 4.24 to 85.03), compounding or manufacturing issues (8.51, 5.17 to 14.0), and hospitalisation (2.35, 1.94 to 2.83)4.
The same analysis found lower reporting odds for administration errors (0.29, 0.16 to 0.53) and dosing errors (0.24, 0.17 to 0.32) among compounded products4. That is the opposite direction, it is in the same paper, and leaving it out would be exactly the selective reading this site exists to argue against.
A reporting odds ratio from a spontaneous-reporting system is not incidence and not causation. The authors say so themselves. What it does establish is that the failure modes people report for compounded products are weighted toward preparation and quality rather than toward the pharmacology.
Two molecules that cannot be compounded at all
FDA states that retatrutide and cagrilintide cannot be used in compounding under federal law, that they are not components of FDA-approved drugs, and that they have not been found safe and effective for any condition. The agency further states that it has warned telehealth companies for marketing unapproved drugs such as retatrutide, active pharmaceutical ingredient distributors for selling retatrutide and other GLP-1 drugs to compounders, and outsourcing facilities for repackaging retatrutide3.
Our retatrutide and cagrilintide pages are editorial for exactly this reason: there are real phase 2 and phase 3 data worth reading, and no lawful compounded route to either molecule.
How far the trial evidence travels
Same molecule, same base form, same route, same schedule, made under inspected conditions — the trial evidence is a reasonable guide.
Different salt form — the trial evidence does not attach, on FDA's own account of what is and is not known about those salts.
Different concentration or a doses-per-vial arithmetic step — the efficacy evidence may travel while the safety margin narrows, because the error is now in the preparation.
Molecule with no approved product anywhere — there is no trial article to compare against, and the question becomes what is in the vial at all.
Frequently asked questions
Is compounded semaglutide the same as the approved product?
Not necessarily. FDA has stated that some semaglutide products sold by compounders may be salt forms — semaglutide sodium and semaglutide acetate — which it describes as different active ingredients than those used in the approved drugs, adding that it does not have information on whether those salts share the same chemical and pharmacologic properties and is not aware of any lawful basis for their use in compounding.
Does FDA review compounded drugs before they are sold?
No. FDA states that compounded drugs are not FDA-approved and that it does not verify their safety, effectiveness or quality before they are marketed. It also states that compounded drugs should only be used in patients whose medical needs cannot be met by an FDA-approved drug.
Are more adverse events reported for compounded GLP-1 products?
FDA states it had received 990 reports for compounded semaglutide and more than 730 for compounded tirzepatide as of 31 May 2026, while noting these are likely underreported. A FAERS analysis of 81,078 GLP-1 reports from 2018 to 2024 found 707 involving compounded products, with higher reporting odds for preparation errors, contamination and hospitalisation — and lower reporting odds for administration and dosing errors. Reporting odds ratios are not incidence and do not establish causation.
Can retatrutide be compounded?
FDA states that retatrutide and cagrilintide cannot be used in compounding under federal law, that neither is a component of an FDA-approved drug, and that neither has been found safe and effective for any condition. The agency also says it has warned telehealth companies, API distributors and outsourcing facilities in connection with retatrutide.
References
- Wilding JPH et al (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. https://pubmed.ncbi.nlm.nih.gov/33567185/
- U.S. Food and Drug Administration (2026). Compounding and the FDA: Questions and Answers. FDA.gov. https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers
- U.S. Food and Drug Administration (2026). FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. FDA.gov. https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/medications-containing-semaglutide-marketed-type-2-diabetes-or-weight-loss
- McCall KL et al (2026). Safety analysis of compounded GLP-1 receptor agonists: a pharmacovigilance study using the FDA adverse event reporting system. Expert Opin Drug Saf. https://pubmed.ncbi.nlm.nih.gov/40285721/
Medical disclaimer: This content is for general educational purposes only and is not medical advice, diagnosis, or treatment. Always consult a licensed healthcare professional before starting, stopping, or changing any treatment.
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