Over the past year, industry has had a front row seat as the Food and Drug Administration (“FDA” or the “Agency”) decides just how much leeway it wants to afford the manufacture, marketing, and sale of peptide products, and just where it wants to draw the line. Despite the recent decision of FDA’s Pharmacy Compounding Advisory Committee (“PCAC”) to recommend a number of peptides for inclusion on the 503A bulks list process — a move that represents a potentially more permissive stance toward peptide regulation, at least in terms of what can and cannot be compounded under 503A — the Agency continues to draw a line in the sand, communicating that it will not tolerate the sale of unapproved peptide products outside of what appears to be a quasi-sanctioned compounding framework. For example, FDA recently issued warning letters to four peptide sellers for allegedly marketing unapproved new drugs in violation of the Federal Food, Drug, and Cosmetic Act (“FD&C Act”).[1] The letters follow a consistent enforcement playbook: the Agency reviews company websites, identifies drug-type claims embedded in product labeling and marketing content, and determines that the peptide products are being marketed as drugs without approved drug applications. Bottom line — FDA is continuing to illustrate what it deems to be impermissible direct-to-consumer (“DTC”) peptide sales.
A. The Warning Letters: Who Was Targeted and Why
All four warning letters were dated August 24, 2026 and issued by the Office of Unapproved Drugs and Labeling Compliance within CDER. As noted above, each letter was triggered by an FDA review of the recipient’s website conducted in July 2026. The letters share a strikingly uniform structure: FDA identified specific peptides sold on each company’s website, cited examples of product labeling and marketing claims that objectively establish the product’s intended use as a drug under Section 201(g)(1) of the FD&C Act, and concluded that the products are unapproved new drugs under Section 505(a) of the FD&C Act.
Specifically, FDA cited the following products and violative marketing practices:
- Royal Peptides LLC: FDA identified seven peptides — Tirzepatide, Semaglutide, Retatrutide, SS-31 (Elamipretide), PT-141, Tesamorelin, and Bimorelin — marketed as unapproved new drugs. The Agency cited marketing claims touting the products’ effects on weight loss, metabolic regulation, mitochondrial function, sexual dysfunction, and growth hormone signaling. FDA also noted that the company marketed bacteriostatic water alongside a “peptide guide" and “peptide calculator," which collectively provide the means to prepare an injectable drug for human administration — undermining the company’s “for research use only” disclaimers.
- Peptide Partners LLC: FDA identified seven peptides — GLP-1 S (Semaglutide), GLP-2 T (Tirzepatide), GLP-3 Reta (Retatrutide), SS-31 (Elamipretide), Tesa Peptide (Tesamorelin), PT-141 (Bremelanotide), and Reconstitution Solution (BAC) — marketed as unapproved new drugs. Marketing claims included statements about bone health, improved metabolism, neuroprotective effects, kidney protection, cancer treatment potential, and sexual function. Notably, FDA also classified the company’s bacteriostatic water product as a drug because it was sold alongside the peptide products for the purpose of reconstituting them for injection.
- NuScience Peptides LLC: FDA identified nine peptides — GLP-2 Tirz Peptide, GLP-1 Sema Research Peptide, GLP-3 RT (Retatrutide) Research Peptide, Survodutide, Mazdutide, PT-141 Peptide (Bremelanotide), Tesamorelin Research Peptide, Tesamorelin Ipamorelin Blend, and Bacteriostatic water for Peptides (BAC Water) — marketed as unapproved new drugs. NuScience’s product lineup is arguably the broadest of the four, and notably includes two newer incretin-receptor agonists, Survodutide and Mazdutide, that are still in clinical trials and do not yet have any approved commercial applications. FDA cited claims regarding metabolic regulation, weight loss, fatty liver disease treatment, cognitive function, and sexual behavior modulation. As with the other letters, FDA treated the company’s bacteriostatic water as a drug product and rejected the company’s “for laboratory, research, and analytical use" disclaimers.
- Peak Performance Peptides: FDA identified six peptides — Bac water, GLP-3R (Retatrutide), Semaglutide, SS-31, PT-141, and Tesamorelin — marketed as unapproved new drugs. The marketing claims followed the same general pattern as the other three letters, referencing metabolic regulation, appetite suppression, mitochondrial function, sexual arousal, and growth hormone signaling. Similarly, FDA also cited the sale of bacteriostatic water as evidence that the company intended its products to be used as injectable drugs.
B. Common Threads: What FDA Considered Violative
Several common enforcement themes emerge from a side-by-side reading of the four letters:
- “Research use only” disclaimers do not insulate peptide sellers from enforcement. Every company included some version of a “for research use only” or “not for human consumption” disclaimer on its product labeling. FDA dismissed these disclaimers in all four cases, relying instead on objective evidence of intended use under 21 CFR § 201.128 — including the nature of the marketing claims, the sale of bacteriostatic water and reconstitution supplies, and, in some cases, the availability of “peptide calculators” and dosing guides that collectively demonstrate an objective intent that the peptides be used for human injection.
- Website-based marketing claims are sufficient to establish intended use. All four letters were based solely on FDA’s review of the companies’ websites, not on facility inspections, product testing, adverse event reports, or the like. FDA systematically catalogued specific claims from product pages, blog posts, and marketing copy that described the products’ effects on disease states or bodily functions. The lesson here is clear — what a company puts on its website is product labeling, and that labeling alone can trigger enforcement.
- In the peptide space specifically, bacteriostatic water and reconstitution supplies are treated as drug products. Three of the four companies sold bacteriostatic water alongside their peptide products and, in each case, FDA classified the bacteriostatic water itself as a drug, reasoning that selling it alongside demonstrated an intended drug use for both the bacteriostatic water and the peptide.
- Injectable products receive heightened scrutiny. Each letter included a paragraph emphasizing FDA’s particular public health concerns associated with injectable drug products, which “bypass some of the body’s key defenses against toxins and microorganisms that can lead to serious and life-threatening conditions.” This boilerplate language reflects FDA’s view that the injectable nature of these products amplifies the enforcement urgency.
- None of the peptides cited in any of the letters are currently under consideration by the PCAC for nomination on the 503A Bulks List, meaning that FDA considers the marketing of these peptides for therapeutic purposes without an approved new drug application to be illegal under the FD&C Act, and has not expressed any intent to change its stance on these particular peptides moving forward.
C. Takeaways: The Broader Peptide Regulatory Landscape
As discussed above, these warning letters do not exist in a vacuum. Rather, they arrive at a critical inflection point in the federal regulatory treatment of peptides, and they should be read alongside the broader policy developments we have been tracking throughout 2026.
These developments suggest that FDA is pursuing a dual-track approach. On one track, the Agency is moving toward expanded access for certain peptides through the 503A bulks list process. As we wrote about here, FDA removed 12 peptides from the Category 2 list under the Biden administration (removing the “significant safety risk” designation), but the PCAC voted this summer to recommend six of those peptides (i.e., BPC-157, KPV, TB-500, MOTS-c, Epitalon, and Semax) for re-inclusion on the 503A bulks list, and a second PCAC meeting is expected before February 2027 to consider additional peptides (i.e., Cathelicidin (LL-37), GHK-Cu, Dihexa acetate, Melanotan II, Mechano Growth Factor, Pegylated (PEG-MGF)). On the other track, as these warning letters demonstrate, FDA is simultaneously cracking down on everything else (i.e., peptides not currently under review by the PCAC).
It seems that FDA views expanded access and heightened enforcement as complementary, rather than contradictory. Accordingly, as the Agency has publicized, it intends to construct a regulatory environment in which select peptides are available through legitimate, regulated channels (e.g., licensed compounding pharmacies operating under Section 503A), while shutting down the unregulated DTC gray market that has proliferated around peptides generally. Thus, the “verified compounder” model, teased by the administration earlier this year (and discussed in greater detail here) appears to be taking shape. If this is the case, it would mean greater freedom to compound select peptides through legalized pathways (e.g., 503A), balanced by heightened inspection, monitoring, and enforcement for companies that attempt to circumvent this regulatory framework by peddling peptides through illicit channels. And companies that interpret FDA’s evolving posture as implicit permission to sell any peptide without going through proper regulatory channels may be exposing themselves to significant legal liability. With respect to the substances being considered by the PCAC, unless and until they are formally placed on the 503A Bulks List through notice-and-comment rulemaking — a process that could extend well into 2027 or 2028 — FDA appears to consider them unapproved new drugs subject to enforcement, just as it considers peptides that are not currently on or being considered for inclusion by the PCAC, when promoted and/or sold for a therapeutic purpose.
Thus, advertising and promotion remain high-risk areas, subject to close FDA scrutiny. As we’ve previously discussed, FDA’s historic enforcement posture in the GLP-1 space has included warning letters targeting compounding pharmacies and telehealth platforms for misleading advertising and unsubstantiated therapeutic claims. The August 2026 letters extend that pattern to DTC peptide sellers selling GLP-1s and other peptides, suggesting that the Agency is casting a wide net. Companies in the peptide space — whether compounders, telehealth platforms, or retail sellers — may benefit from conducting a thorough review of all public-facing marketing content and ensuring that no claims (implicit or explicit) are being made that could establish an intended drug use for an unapproved product.
And FDA regulation is only one layer of the compliance landscape — state regulation constitutes another layer of the broader peptide regulatory landscape. As we have previously discussed, state boards of pharmacy maintain independent authority over compounding practices, and several states — including Alabama, Ohio, California, and New York — have adopted positions on peptide compounding that are more restrictive than the federal framework. Companies managing multi-state operations should conduct a jurisdiction-by-jurisdiction assessment of applicable state requirements and should not assume that federal developments, including a potentially favorable PCAC recommendation for a specific peptide, will override more restrictive state-level restrictions.
These recent letters, taken in the context of the broader regulatory landscape for peptide products, provide companies with an actionable compliance imperative: align with the evolving regulatory framework on both the state and federal level, engage with the 503A bulks list process (as applicable for the specific peptide you intend to market), and clean up public-facing marketing before FDA comes knocking.
FOOTNOTES
[1] See Letter to Peak Performance Peptides; Letter to Peptide Partners, LLC; Letter to NuScience Peptides, LLC; Letter to Royal Peptides, LLC.