What "essentially a copy" means, and why it decides whether a compounded GLP-1 is lawful

The whole legal argument about compounded semaglutide and tirzepatide since early 2025 turns on nine words in section 503A: "essentially a copy of a commercially available drug product." Here is what the statute says, what FDA's 2018 guidance adds, and how it applies to the vial a telehealth program is offering you.

The statutory text

Section 503A(b)(1)(D) conditions the exemption on the compounder not compounding "regularly or in inordinate amounts (as defined by the Secretary) any drug products that are essentially copies of a commercially available drug product." The same subsection then defines the exception: the phrase "does not include a drug product in which there is a change, made for an identified individual patient, which produces for that patient a significant difference, as determined by the prescribing practitioner, between the compounded drug and the comparable commercially available drug product."

Three things are in that text and are easy to miss. The change must be for an identified individual patient. The difference must be significant for that patient. And the person who determines it is the prescriber, not the pharmacy and not the patient.

What FDA's 2018 guidance adds

FDA finalised its 503A guidance on this provision in January 2018 (Federal Register notice January 19, 2018). Its main points:

• Identical or nearly identical. A compounded drug is essentially a copy if it has the same active ingredient, route, dosage form and strength as a commercially available product, or is nearly so. Small changes that do not matter clinically do not take a product out of the definition.
• Commercially available means an approved product that is actually on the market. A drug on FDA's shortage list is treated as not commercially available for this purpose, which is the hinge the whole 2022 to 2025 GLP-1 compounding period swung on. When the shortage listing ended, the approved product became commercially available again and the copy analysis switched back on.
• Documentation. The prescriber's determination of significant difference should be noted on the prescription or otherwise available to the pharmacy. FDA gives examples of adequate notes ("no dye, patient allergy") and says a generic statement that the compounded product is "different" is not enough.
• Regularly or in inordinate amounts. FDA's later GLP-1 page states the operating rule in one sentence: the agency does not intend to take action where a pharmacy fills four or fewer prescriptions for essentially identical copies in a calendar month. Above that, the compounder needs the patient-specific difference for each prescription.

Applying it to a compounded GLP-1

Work through the questions in order.

1. Is there a commercially available comparator? For semaglutide injection, yes since February 21, 2025 (Ozempic and Wegovy). For tirzepatide injection, yes since December 19, 2024 (Mounjaro and Zepbound). Dates are FDA's; see the shortage timeline.
2. Same active ingredient, route, form and strength? A vial of semaglutide base for subcutaneous injection at a strength the pens provide is identical or nearly identical. A salt form is a different question, and not a favourable one; see salt forms and research use only.
3. Is there a change for you specifically? A documented allergy to an excipient, an inability to use a pen device, a dose the approved product cannot deliver and that your prescriber judges necessary: these are the kinds of differences the guidance contemplates. "It is cheaper" is not a clinical difference. "Everyone gets B12 added" is not patient-specific.
4. Did the prescriber make and record the determination? Ask to see it. If the pharmacy or the program supplies a standard sentence, that is the pattern FDA's 2025 and 2026 warning letters describe.

The 503B version

Section 503B has its own essentially-a-copy provision at 503B(a)(5) and its own 2018 guidance. The test is stricter in one way: for an outsourcing facility, a drug is not a copy only if a prescriber has determined there is a clinical difference for an individual patient, or the drug appears on FDA's shortage list. There is no four-a-month allowance. Combined with the bulk-substance restriction in 503B(a)(2)(A), it is the reason FDA proposed on April 30, 2026 to exclude semaglutide, tirzepatide and liraglutide from the 503B bulks list altogether; see what compounders may do now.

What this means when you are offered a compounded GLP-1

You are entitled to ask the program two questions: which approved product is this a variation of, and what is the documented difference for me. The vetting checklist puts both on paper. FormBlends' own regulatory status page explains how it approaches the same requirement for its dispensed products; read it with the same questions in mind.