FDA Peptide Warning Letters Reject Research Use Only Labels

The U.S. Food and Drug Administration (FDA) sent warning letters dated August 24, 2026, through its Center for Drug Evaluation and Research (CDER) to five online peptide sellers, telling each one that injectable products on its website are unapproved new drugs even though each site labeled them for research use. The recipients are Peak Performance Peptides of Phoenix; Royal Peptides LLC of Boynton Beach, Florida; NuScience Peptides LLC of Cornelius, North Carolina; Peptide Partners LLC of Sarasota, Florida; and TXP Innovations LLC, which does business as Tex Peptides, in Dallas.

Every letter answers the disclaimer in a footnote. The version sent to Peak Performance reads: “Despite statements on your product labeling marketing your products for ‘research use only’ and ‘not for human consumption,’ evidence obtained from your website establishes that your products are intended to be drugs for human use.” The rest of each letter lists that evidence page by page, which makes the batch a detailed public record of the storefront features FDA treats as proof of intended human use.

What the five letters say

All five letters are signed by Tina Smith, director of CDER’s Office of Unapproved Drugs and Labeling Compliance, and each says FDA reviewed the company’s website in July 2026. The agency concluded that the listed products are “new drugs” with no approved application in effect, so shipping them across state lines violates sections 301(d) and 505(a) of the Federal Food, Drug, and Cosmetic Act. FDA posted the letters on its warning letter database on September 1.

The letters call the products especially concerning because “injectable drug products can pose risks of serious harm to users.” Each asks for a written response within 15 business days of receipt, describing corrective steps, and invites the company to send information if it believes its products do not violate the law. Each also warns that failing to fix the violations “may result in regulatory or legal action without further notice including, without limitation, seizure and injunction.”

A warning letter records FDA’s findings from its own review of each site. It is not a court ruling, and the companies can contest the agency’s conclusions in their responses.

Products cited, from GLP-1 drugs to SS-31

Semaglutide, retatrutide, PT-141 (bremelanotide), and tesamorelin appear in all five letters. SS-31, also called elamipretide, appears in four. The full lists, using the product names as the letters give them:

Company	Products FDA called unapproved new drugs
Peak Performance Peptides	“GLP-3R” (retatrutide), semaglutide, SS-31, PT-141, tesamorelin, “Bac water”
Royal Peptides LLC	Tirzepatide, semaglutide, retatrutide, SS-31 (elamipretide), PT-141, tesamorelin, “BIMORELIN” (a tesamorelin and ipamorelin blend)
NuScience Peptides LLC	“GLP-2 Tirz Peptide,” “GLP-1 Sema Research Peptide,” “GLP-3 RT (Retatrutide) Research Peptide,” survodutide, mazdutide, PT-141 (bremelanotide), tesamorelin, a tesamorelin and ipamorelin blend, bacteriostatic water
Peptide Partners LLC	Semaglutide, tirzepatide, retatrutide, SS-31, tesamorelin, PT-141, “Reconstitution Solution (BAC)”
Tex Peptides	Semaglutide, tirzepatide, retatrutide, SS-31, tesamorelin, PT-141, “Bacteriostatic Water 0.9% Benzyl Alcohol (10 ml)”

The range is wider than in the peptide letters CDER sent earlier this year. On March 31, 2026, CDER wrote to Gram Peptides and Lovega LLC, doing business as Pink Pony Peptides, about retatrutide, tirzepatide, and bacteriostatic water, using the same “Despite statements on your product labeling” reasoning. The August batch carries that reasoning to tesamorelin, a growth hormone-releasing hormone analog; PT-141, which the sites tied to sexual function; SS-31, a mitochondria-targeted peptide one site marketed for “anti-aging”; and two more metabolic peptides, survodutide and mazdutide.

Code names did not change the outcome. Peak Performance sold retatrutide as “GLP-3R,” but the product page FDA cites sits at a web address ending in /product/retatrutide-5mg/, and the letter identifies the compound by name.

The site features FDA cited as evidence of human use

FDA’s legal test is intended use, defined in its regulation at 21 CFR 201.128, and the letters build that case from what each website showed. EC4IM sorted the cited evidence into five groups.

Hedged product copy

Careful wording did not help. Peak Performance’s semaglutide page described the drug as “Studied for effects on insulin secretion and glycemic control,” and its SS-31 page said “Explored for potential neuroprotective and cardiovascular benefits.” FDA quoted both lines as drug claims. Royal Peptides’ SS-31 page paired a research label with health benefits in a single line: “Advanced Research Use: Mitochondrial repair, anti-aging, neuroprotection.” Tex Peptides was blunter about PT-141, calling it “an effective and powerful enhancer for both mood and your senses.”

Study summaries and linked pages

Peptide Partners’ product pages carried plain-language summaries of laboratory research, and FDA treated those summaries as claims. One, on the PT-141 page, said: “This study discovered that bremelanotide can kill brain cancer cells (glioblastoma) grown in laboratory culture dishes without harming normal cells.” Royal Peptides listed journal article titles on its PT-141 page, including “PT-141: a melanocortin agonist for the treatment of sexual dysfunction.”

The NuScience letter goes a step further. To document the semaglutide product, FDA quoted a page on PubChem, a chemistry database run by the National Institutes of Health’s National Library of Medicine, that NuScience had hyperlinked from its product listing: “Weight loss is believed to occur via the reduction of appetite and food cravings after semaglutide administration.” FDA counted a third-party page the store linked to as evidence of how the store intended its product to be used.

Blog and comparison articles

Royal Peptides’ letter cites two comparison articles on its site, not only its shop pages. One lists “Benefits of Tirzepatide,” including “Promotes sustainable weight loss” and “Once-weekly injection for convenience,” and lists “Once-weekly dosing” among the benefits of retatrutide. Articles outside the shop pages carried the same weight in the letter as product descriptions.

Bacteriostatic water in the same catalog

Bacteriostatic water is sterile water with a preservative, commonly used to reconstitute powdered drugs before injection. Four of the five letters list it as an unapproved drug in its own right. The Peak Performance letter states the reasoning in two sentences: “The sale of these products together demonstrates that you intend for your ‘Bac water’ to be used in combination for injection. Therefore, your ‘Bac water’ is a drug.” The Royal Peptides letter does not list the water as a separate violation but cites its sale alongside the peptides as evidence.

Calculators and guides

Two letters name on-site tools. FDA told NuScience that it markets bacteriostatic water “alongside a ‘peptide calculator,’ a resource that provides the means to prepare an injectable drug for human administration.” Royal Peptides’ letter cites a “peptide guide” and “peptide calculator,” which FDA called “resources that collectively provide the means to prepare an injectable drug for human administration.”

What the letters do not say

A September 18 alert from the law firm ArentFox Schiff described the agency as looking “past the label to the net impression of the website as a whole” and counted dosing guidance among the factors. That is the firm’s framing. The five letters themselves speak of “evidence obtained from your website,” and none uses the phrase “dosing guidance,” although Royal Peptides’ quoted blog copy refers to once-weekly injection and dosing.

The letters also do not tell the vendors that rewriting copy or removing a calculator would make the products lawful. FDA’s conclusion is that the products are unapproved new drugs, and each letter notes that its list “is not intended to be an all-inclusive list of the violations” connected to the company’s products or operations.

Why the same pages matter in a payments review

Analysis. The letters read like an inspection checklist that anyone can apply to a peptide or longevity storefront: product copy, linked research, blog posts, calculators, and companion supplies such as bacteriostatic water. Risk teams at acquiring banks and payment facilitators commonly review a merchant’s live site when they approve an account and again during monitoring, so the pages FDA documented in July are the same pages an underwriter would capture. A posted warning letter that names the merchant’s domain is also simple to find in a routine search.

The research-use disclaimer does no more work in that review than it did for FDA. A merchant application that describes injectable peptides as laboratory reagents, while the site sells reconstitution water and hosts a peptide calculator, presents the contradiction FDA documented. Where an acquirer concludes the products are unapproved drugs, its options include reserves, holds, or closing the account, tools EC4IM described in its explainer on reserves, rolling reserves, and account holds.

The batch also marks a boundary that helps legitimate supplement and wellness brands. A company selling capsules and powders as dietary supplements, and applying for processing through a supplement-focused intermediary like Organic Payment Gateways, stands in a different position from a store listing injectable peptides beside bacteriostatic water, which FDA’s letters classify as unapproved drugs whatever merchant category the account sits in.

FDA has pressed other corners of the same market with different tools, including warning letters to 30 telehealth firms over compounded GLP-1 marketing claims and a letter citing Empower Pharmacy’s compounded GLP-1 telehealth menus. The August 24 letters need neither a compounding theory nor a misleading-advertising theory, only evidence that a website sold injectable drugs FDA has not approved.

Response deadline and open questions

The 15-business-day response window in each letter runs from the date the company received it, which FDA’s posting does not give. As of October 8, FDA’s warning letter database listed no response or close-out letters for any of the five companies. EC4IM did not contact the companies before publication, and their responses, if any, have not been made public.

The August 24 letters turn a familiar legal position into a detailed map of storefront evidence. FDA held that research-only labels did not outweigh product pages describing effects on the body, study summaries and linked databases, blog comparisons that mention weekly injections, bacteriostatic water sold in the same catalog, and peptide calculators that FDA said provide the means to prepare an injectable drug. For peptide sellers, the letters show how the agency reads a website; for the banks and processors that review those sites, they supply a public record of which pages carry that risk.

FDA Peptide Warning Letters Show Research Use Only Labels Did Not Shield Online Vendors