FDA classified retatrutide as a drug in March 2024, and Eli Lilly sued to have it treated as a biologic. A federal court in Indiana upheld FDA’s reading of the protein definition but set aside its “analogous product” reasoning. Lilly appealed. As of October 9, 2026, the Seventh Circuit has heard argument and has not ruled. Either way, retatrutide is unapproved, and FDA says it cannot be compounded.
The case matters to you because the label decides who could ever compound retatrutide after approval. It does not change what you can lawfully offer today.
The line between a drug and a biologic is drawn at 40 amino acids
The Public Health Service Act defines a “biological product” to include a “protein, or analogous product” applicable to the prevention, treatment, or cure of a disease or condition of human beings (42 U.S.C. § 262(i)(1)). Congress did not define “protein.” FDA did, in 21 CFR § 600.3(h)(6): “any alpha amino acid polymer with a specific, defined sequence that is greater than 40 amino acids in size.” When two or more chains are associated “in a manner that occurs in nature,” size is based on “the total number of amino acids in those chains.”
That line already moved products once. On March 23, 2020, approved applications for biological products under the drug statute were “deemed to be a license” under section 351, per section 7002(e)(4)(A) of the Biologics Price Competition and Innovation Act. Congress had also removed the “(except any chemically synthesized polypeptide)” carve-out from the protein category in December 2019. FDA’s transition list includes tesamorelin, sold as Egrifta and Egrifta SV. That is why our tesamorelin tracker shows no compounding pathway for it.
Retatrutide sits one amino acid from the line
Lilly filed a request for designation on November 9, 2023 and a superseding request on January 29, 2024. As the court summarized it, Lilly described retatrutide as 41 amino acids in total: a backbone of 39 alpha amino acids plus an associated chain of one gamma-glutamate and one ADO residue.
On March 18, 2024, FDA designated retatrutide a drug. FDA counted at most 40 alpha amino acids and one non-alpha amino acid, and held that a protein needs more than 40 alpha amino acids. FDA also said retatrutide is not “analogous” to a protein because it lacks that “fundamental, defining property.”
The Indiana court split the case in two
Lilly sued on September 3, 2024 (S.D. Ind. No. 1:24-cv-01503). The court ruled on September 30, 2025 and issued an amended order on October 3, 2025.
- Protein claim: FDA won. The court held that “the regulation unambiguously requires that proteins contain at least forty-one alpha amino acids.” Because retatrutide has 40 at most, FDA did not violate its own regulation.
- Analogous product claim: Lilly won. The court found that requiring an “analogous” product to meet every element of the protein definition “effectively reads ‘analogous product’ out of the statute.” It set that portion of the decision aside as arbitrary and capricious and remanded for FDA to identify, “in a uniform fashion,” the defining feature of analogous products. The court added there is a “meaningful possibility that the agency could lawfully reach the same conclusion.”
The final judgment of December 16, 2025 “VACATES the agency’s designation decision and REMANDS to the agency for further proceedings on Plaintiff’s ‘analogous’ products claim.” The court declined to order FDA to designate retatrutide a biologic. Lilly filed its notice of appeal on February 12, 2026.
The appeal has been argued and turns first on jurisdiction
The Seventh Circuit docketed No. 26-1301 on February 17, 2026. Lilly filed its opening brief April 1, the government responded May 15, the Outsourcing Facilities Association filed an amicus brief supporting FDA on May 19, and Lilly replied June 5.
The panel heard argument on September 24, 2026. The same day it ordered supplemental memoranda on appellate jurisdiction, covering how appeals by private parties from remands to agencies have been treated. Both sides submitted them on October 8, 2026. As of October 9, 2026, there is no ruling.
Each side’s argument, in the words of the briefs
Lilly. The regulation counts “the total number of amino acids,” and retatrutide has 41, “a number plainly ‘greater than 40.’” The definition uses “alpha” for the polymer and omits it from the size requirement, so all amino acids count. Lilly points out that FDA licensed Sogroya as a biologic although it includes non-alpha ADO units. Lilly also argues that once the court vacated FDA’s decision, the 60-day designation deadline in 21 U.S.C. § 360bbb-2 meant Lilly’s own recommendation took effect. Its June reply says “almost six months have now passed” with “no FDA action in sight.”
FDA. Protein is a scientific term, and alpha amino acids are “the building blocks of proteins.” Non-alpha amino acids “cannot form peptide bonds,” so restating “alpha” in the size clause would have been redundant. The deadline argument concerns a remand decision FDA “has not yet issued” and is not properly before the court, and the statute covers a missed decision, not a timely one later vacated. FDA also notes that remand orders are generally not final, appealable decisions.
The 503B trade group. The Outsourcing Facilities Association argues biologic status brings Lilly longer exclusivity and “potential limits on compounding,” noting that “manufacturers generally contend that the law forbids the compounding of biologics.” It calls compounding a safety valve during shortages and a source of custom formulations.
The label decides which compounding doors could ever open
| Drug path (NDA) | Biologic path (BLA) | |
|---|---|---|
| Governing statute | FD&C Act § 505 | PHS Act § 351 |
| Follow-on route | Generic or 505(b)(2) application | Biosimilar under § 351(k) |
| Exclusivity before follow-on | 5 years for a new chemical entity, 21 U.S.C. § 355(c)(3)(E) | 12 years from first licensure, 42 U.S.C. § 262(k)(7)(A) |
| 503A after approval | Possible in principle as a component of an approved drug, § 503A(b)(1)(A)(i)(II), subject to the limit on essentially copies, § 503A(b)(1)(D) | FDA: not eligible for 503A exemptions and not considered for the 503A bulks list |
| 503B after approval | Only via the 503B bulks list or the drug shortage list, § 503B(a)(2) | No compounding pathway in FDA’s 503A policy; mixing and repackaging governed by separate FDA guidance |
| Status today | Unapproved. FDA: cannot be compounded | Unapproved. FDA: cannot be compounded |
The biologic row rests on FDA’s January 2025 interim 503A policy, which states that biological products subject to approval in a BLA “are not eligible for the exemptions in section 503A.” Lilly’s August 5, 2026 earnings release, filed with the SEC, says it plans to submit a Biologics License Application in the first quarter of 2027. That is a company plan.
The bottom row is the one that applies to you. FDA’s GLP-1 page, current as of October 1, 2026, states: “Retatrutide and cagrilintide cannot be used in compounding under federal law.” See our retatrutide status page and why there is no legal way to prescribe or compound it.
What this means for you
Nothing changes on your menu. Our providers do not prescribe retatrutide, and no ruling in this appeal creates a lawful product. A win for Lilly would make retatrutide a biologic, which under FDA’s policy keeps it out of 503A compounding even after approval. A win for FDA keeps it a drug, which opens nothing until approval and then only within the 503A limits described above. Plan your weight management program around approved therapies, ask your pharmacy how it applies the 503A and 503B rules to every peptide it supplies, and book a call if you want that review done with you.
Frequently asked questions
Is retatrutide a biologic or a drug?
As of October 9, 2026, FDA’s position is that retatrutide is a drug because it has at most 40 alpha amino acids, below the protein threshold in 21 CFR 600.3(h)(6). A federal court upheld that reading but vacated FDA’s designation decision on a separate “analogous product” issue. Lilly’s appeal is pending in the Seventh Circuit.
What did the court decide in Lilly v. Kennedy?
The Southern District of Indiana held that the regulation unambiguously requires at least 41 alpha amino acids, so FDA correctly found retatrutide is not a protein. It held FDA’s “analogous product” reasoning arbitrary and capricious, vacated the designation decision, and remanded that issue to FDA. It did not order FDA to classify retatrutide as a biologic.
Can retatrutide be compounded if Lilly wins?
No. Retatrutide is unapproved, and FDA states it cannot be used in compounding under federal law. If it were classified as a biologic and later approved, FDA’s 503A policy says biological products subject to a BLA are not eligible for 503A exemptions. A Lilly win would narrow compounding options further.
When will the Seventh Circuit rule?
There is no set date. The court heard argument on September 24, 2026 and asked both sides for supplemental memoranda on whether it has appellate jurisdiction over an appeal from a remand to an agency. Both sides submitted them on October 8, 2026. As of October 9, 2026, no ruling has issued.
This is general information, not legal advice. Rules vary by state and change. Confirm your own facts with counsel.