How the United States came to regulate research-use-only peptides the way it does: the statutes and court decisions that make up the law, the regulations that implement it, and the guidance and enforcement that show how FDA reads it today. Each entry gives its citation.
Statute
Pure Food and Drug Act
The first federal food and drug law. It prohibited adulterated and misbranded drugs in interstate commerce, but required no approval before a drug was sold.
Pub. L. 59-384, 34 Stat. 768
Statute
Federal Food, Drug, and Cosmetic Act
Replaced the 1906 Act. It defined a drug by its intended use, in section 201(g)(1), and required evidence of safety before a new drug could be marketed. The definition by intended use is the foundation of every research-use-only case since.
Pub. L. 75-717, 52 Stat. 1040 · What "research use only" means in law
Court decision
United States v. Dotterweich
The Supreme Court held that a company officer can be criminally liable for shipping adulterated or misbranded drugs without proof that the officer knew of the violation.
320 U.S. 277 (1943)
Statute
Durham–Humphrey Amendment
Separated prescription drugs from those sold over the counter: a drug that is not safe to use without professional supervision may be dispensed only on prescription.
Pub. L. 82-215, 65 Stat. 648
Statute
Kefauver–Harris Drug Amendments
Required substantial evidence of effectiveness, as well as safety, before a new drug could be approved, from adequate and well-controlled investigations.
Pub. L. 87-781, 76 Stat. 780
Court decision
United States v. Park
Confirmed the responsible corporate officer doctrine: an executive with the authority and responsibility to prevent or correct a violation can be held liable for it.
421 U.S. 658 (1975) · What "research use only" means in law
Statute
Food and Drug Administration Modernization Act: section 503A
Set the conditions under which pharmacists and physicians may compound drugs exempt from new drug approval, including which bulk drug substances they may use.
Pub. L. 105-115, 111 Stat. 2296
Court decision
Thompson v. Western States Medical Center
The Supreme Court struck down section 503A's restrictions on advertising and promoting compounded drugs as a violation of the First Amendment.
535 U.S. 357 (2002)
Statute
Biologics Price Competition and Innovation Act
Added "protein (except any chemically synthesized polypeptide)" to the statutory definition of a biological product, and provided that proteins approved as drugs would be deemed to hold biologics licenses ten years later.
Pub. L. 111-148, title VII, subtitle A
FDA guidance
Guidance on in vitro diagnostic products labeled for research use only
FDA's final guidance on diagnostic products labeled "for research use only": the label does not decide the product's status when the manufacturer's conduct shows it is intended for clinical diagnostic use. It concerns diagnostic devices, but it sets out the principle FDA applies to research chemicals too: intended use is judged from all of the evidence. Guidance is not binding and can be revised.
78 FR 70306 · How the FDA decides what a product is for
Statute
Drug Quality and Security Act
Created section 503B outsourcing facilities and removed from section 503A the advertising provisions struck down in 2002.
Pub. L. 113-54, 127 Stat. 587
Regulation
Definition of the term "biological product"
FDA defined a protein as an alpha amino acid polymer with a specific, defined sequence of more than 40 amino acids. From 23 March 2020, approved protein drugs were deemed biologics licenses; peptides of 40 amino acids or fewer remain drugs. Congress had removed the exception for chemically synthesized polypeptides in the Further Consolidated Appropriations Act, 2020, so the 40-amino-acid line applies however a chain is made.
85 FR 10057; effective 23 March 2020
Regulation
Regulations regarding "intended uses"
FDA amended 21 CFR 201.128 and 801.4 to say that intended use may be shown by any relevant source of evidence, and that a firm's knowledge that its product is used for an unapproved purpose is not, on its own, enough to establish intended use.
86 FR 41383; effective 1 September 2021 · How the FDA decides what a product is for
Enforcement
First warning letter in the enforcement tracker
The earliest FDA warning letter in our tracker to an online seller of research-labeled peptide products. Like every letter since, it quotes the seller's research-use disclaimer and finds intended use from the rest of the website. Warning letters are FDA's interpretation in a particular case, informal and advisory, and not final agency action.
FDA reference 668918 · FDA enforcement tracker
Court decision
Loper Bright Enterprises v. Raimondo
The Supreme Court overruled Chevron deference: courts must decide for themselves what a statute means, rather than defer to an agency's reasonable interpretation of an ambiguous one. How far this changes the reading of the drug definition and intended use has yet to be tested.
603 U.S. 369 (2024) · Who decides what a product is for?
Private litigation
A manufacturer sues a research-labeled seller
Eli Lilly sues a Washington seller of "research grade" tirzepatide under the state consumer-protection act, after a cease-and-desist letter. The case settles in May 2025 with the court retaining jurisdiction: the template for the manufacturer suits of 2026.
No. 2:24-cv-01719 (W.D. Wash.) · Lilly's retatrutide lawsuits: what the dockets say
Court decision
Zyla Life Sciences v. Wells Pharma of Houston
The Fifth Circuit holds that state laws forbidding the sale of unapproved new drugs, because they copy federal law, are not preempted by the FDCA, so a competitor may sue under them even though the federal Act itself gives no private right of action. The Ninth Circuit had reached the opposite result in 2022; the Supreme Court declined to resolve the split.
No. 23-20533 (5th Cir. 2025); cert. denied June 29, 2026 · Lilly's retatrutide lawsuits: what the dockets say
Private litigation
Six manufacturer suits over an investigational molecule
Eli Lilly sues a compounding pharmacy, a medical spa chain and four research-labeled online sellers over retatrutide, a molecule no one may yet sell for human use, under eight states' consumer-protection laws and, for the spa, the Lanham Act. Five more suits follow on October 8. Three of the first six are dismissed by Lilly within ten weeks; one motion to dismiss is pending.
S.D. Tex., W.D. Tex., E.D. Tex., E.D. Cal. · Lilly's retatrutide lawsuits: what the dockets say
Enforcement
Warning letters to research-use-only peptide sellers, to date
17 published warning letters to online sellers of research-labeled peptide products are in the tracker: 5 in 2024, 1 in 2025, 11 in 2026. The record is kept current on the tracker page. FDA's approach in these letters is its interpretation and may change.
17 letters; latest FDA reference 733652 · FDA enforcement tracker
See also
Cite this page
Text
Cosmic Peptides. (2026, October 25). Regulatory timeline: research-use-only peptides. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/regulatory-timeline
BibTeX
@misc{cosmicpeptides_research_regulatory_timeline,
author = {{Cosmic Peptides}},
title = {Regulatory timeline: research-use-only peptides},
howpublished = {Cosmic Peptides Research Library},
year = {2026},
month = oct,
url = {https://cosmicpeptides.com/research/regulatory-timeline},
urldate = {2026-10-26},
note = {Last reviewed 2026-10-25}
} RIS
TY - ELEC AU - Cosmic Peptides TI - Regulatory timeline: research-use-only peptides T2 - Cosmic Peptides Research Library PB - Cosmic Peptides PY - 2026 DA - 2026/10/25 UR - https://cosmicpeptides.com/research/regulatory-timeline Y2 - 2026/10/26 LA - en ER -
Cite the date the page was last reviewed, October 25, 2026, as its version. Reference managers such as Zotero can save this page directly.
Changes to this page
- Updated Lilly's retatrutide lawsuits: what the dockets say
An opinion piece reading the full court record of the eleven suits: the claims pleaded and left out, each docket's status, the standing and preemption questions, how the cases end, and what they will turn on. The regulatory timeline gains the related litigation.
- Published Regulatory timeline
The statutes, court decisions, regulations and FDA guidance that shape research-use-only peptide regulation in the United States, from 1906 to today, each with its citation.
Changes of substance are listed here; wording changes are not. Every correction is also on the corrections log.
For in vitro laboratory research only. Not for human or veterinary use. This library describes chemistry, analytical methods and published laboratory research; it gives no guidance on use in people or animals.