Two FDA Warning Letters on GLP-1 Research Peptides, 2026

By Peptide Ecommerce · October 24, 2026

By our count, FDA named 16 products in two of its warning letters dated August 24, 2026, including semaglutide, tirzepatide and retatrutide research peptides, as unapproved new drugs. Both letters came from FDA's Center for Drug Evaluation and Research, to NuScience Peptides LLC and Peptide Partners LLC, and both reached that finding despite labels marking the products for research use.

To follow every letter FDA has sent to peptide sellers, use the FDA warning letter tracker.

This guide is for founders and operators of research use only (RUO) peptide stores that list, or are thinking about listing, GLP-1 class products. It is a close reading of two letters: what they name, what they find, what evidence they quote, what they demand, and what an operator should audit as a result. Every quotation is copied from the letter or regulation it cites. Where we give our own reading, we say so.

Talk through what these letters mean for your catalog: book a call

What you will be able to do after reading

By the end of this guide you will be able to:

1. List the products the two letters named and how they break down by company. Delivered in Which products did FDA name?.

2. Trace the four legal links FDA used, from drug to violation, in FDA's own words. Delivered in What legal findings did FDA make, in its own words?.

3. Recognize the kinds of website copy FDA quoted as proof of intended use. Delivered in What website statements did FDA quote as proof? and What does "intended use" mean in these letters?.

4. Explain why selling bacteriostatic water was cited. Delivered in Why was selling bacteriostatic water cited?.

5. Run the eight point audit of your own site and track new letters. Delivered in What should a GLP-1 class seller audit on its own site? and How should you track new letters?.

The self check near the end tests each one.

Key Facts

Two of FDA's August 24, 2026 letters, to NuScience Peptides LLC (reference 733652) and Peptide Partners LLC (reference 735063), named 16 products (our count) as unapproved new drugs: nine (our count) in the NuScience letter and seven (our count) in the Peptide Partners letter.
The named products include semaglutide, tirzepatide and retatrutide research peptides, and each letter also names the reconstitution water the company sold.
Both letters find the products are drugs under section 201(g)(1) and new drugs under section 201(p), and state: "No approved applications pursuant to section 505 of the FD&C Act, 21 U.S.C. 355, are in effect for these products."
Both letters say the same thing about the research labels: "evidence obtained from your website establishes that your products are intended to be drugs for human use."
Much of the copy FDA quoted was written as research summaries, for example research summary copy about rodent studies of weight and blood sugar (see the NuScience letter).
FDA treated the water as a drug because of what it was sold with: "The sale of these products together demonstrates that you intend" it "to be used in combination for injection."
Each company was told to respond "within fifteen (15) business days of receipt of this letter" and to "Send your written response to [email protected]."
The site's own tracker data records five FDA warning letters to peptide sellers dated 2026-08-24, out of 11 letters in the data set (see the tracker).

What did FDA tell NuScience Peptides and Peptide Partners?

In the two letters this guide reviewed, FDA told two sellers that their GLP-1 research peptides are unapproved new drugs. Both letters are dated August 24, 2026, and both were issued by FDA's Center for Drug Evaluation and Research. Sources: FDA warning letter to NuScience Peptides LLC, FDA warning letter to Peptide Partners LLC.

Neither letter describes an inspection of a warehouse or a lab. Both open the same way: "This warning letter advises you of significant violations observed during a U.S. Food and Drug Administration (FDA) review of your website." Both say the violations were "identified and documented during a review of your website" and date that review to July 2026. In other words, the evidence in both letters is what a visitor could read on the store. Sources: NuScience letter, Peptide Partners letter.

Both letters also say they are not the full picture. Each states that "It is your responsibility to ensure that your firm complies with all requirements of federal law, including FDA regulations," and each calls itself not "an all-inclusive list of violations that may exist in connection with your products or operations." Our read: a store that fixes only the sentences FDA quoted has not done what the letter asks. Sources: NuScience letter, Peptide Partners letter.

Which products did FDA name?

This section delivers outcome 1 of 5: list the named products.

The letter to NuScience Peptides LLC (reference 733652) lists these products, which FDA says "are unapproved new drugs under section 505(a)": 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). The letter to Peptide Partners LLC (reference 735063) names 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). Sources: FDA warning letter to NuScience Peptides LLC, FDA warning letter to Peptide Partners LLC.

How the products break down

Counting from those two lists (our own count, not FDA's wording), the 16 products fall into four groups:

| Group (our grouping) | NuScience (733652) | Peptide Partners (735063) |

|:--|:--|:--|

| Products sold under GLP-1, GLP-2 or GLP-3 names | GLP-2 Tirz Peptide, GLP-1 Sema Research Peptide, GLP-3 RT (Retatrutide) Research Peptide | GLP-1 S (Semaglutide), GLP-2 T (Tirzepatide), GLP-3 Reta (Retatrutide) |

| Other metabolic research products named | Survodutide, Mazdutide | None |

| Other peptides | PT-141 Peptide (Bremelanotide), Tesamorelin Research Peptide, Tesamorelin Ipamorelin Blend | SS-31 (Elamipretide), Tesa Peptide (Tesamorelin), PT-141 (Bremelanotide) |

| Reconstitution water | Bacteriostatic water for Peptides (BAC Water) | Reconstitution Solution (BAC) |

Source for every product name in the table: NuScience letter and Peptide Partners letter.

Three things stand out for an operator.

First, FDA used the store's own product names, in quotation marks, as the store wrote them. The word Research in "GLP-1 Sema Research Peptide" and "Tesamorelin Research Peptide" sits inside the name FDA listed as an unapproved new drug. Our read: putting research in a product title did not take the product off the list. Source: NuScience letter.

Second, shorthand names did not hide the compound. Both stores used GLP numbering, and both letters still listed the products, in several cases with the compound name in parentheses as the store had it, such as "GLP-3 Reta (Retatrutide)" and "GLP-3 RT (Retatrutide) Research Peptide." Sources: NuScience letter, Peptide Partners letter.

Third, a blend counted as its own product. "Tesamorelin Ipamorelin Blend" appears in the NuScience list next to "Tesamorelin Research Peptide," and FDA quoted a separate product page for it. Source: NuScience letter.

What else the evidence ledger says about each named compound

We checked each named compound against the evidence ledger this site uses. For semaglutide, tirzepatide, retatrutide, survodutide, mazdutide, bremelanotide (PT-141), tesamorelin and SS-31 (elamipretide), the only FDA entries are warning letter entries, these two letters among them. The published FDA compounding pages we hold do not list any of those compounds, so this guide says nothing about their compounding status.

Ipamorelin, which appears only inside the NuScience blend, is the one exception. FDA's page of bulk drug substances that may present significant safety risks lists "Ipamorelin acetate 503B September 29, 2023." That listing concerns compounding, not research product sales, and the NuScience letter does not refer to it. For how compounding lists bear on an RUO catalog, see our guide to the FDA category 2 peptides list.

What legal findings did FDA make, in its own words?

This section delivers outcome 2 of 5: trace the four legal links.

Both letters build the same chain of findings, in the same words. Read in order, by our count it has four links. Sources for every quotation in this section: NuScience letter, Peptide Partners letter.

Link 1: the products are drugs

Each letter (NuScience letter, Peptide Partners letter) says the named products "are drugs under section 201(g)(1) of the FD&C Act, 21 U.S.C. 321(g)(1), because they are intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease, and/or intended to affect the structure or any function of the body." The statute FDA cites defines drugs to include "articles intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease in man or other animals; and (C) articles (other than food) intended to affect the structure or any function of the body of man or other animals" (21 U.S.C. 321).

The word that carries the finding is intended. Neither letter says FDA tested a vial. The finding rests on what the store's own words and catalog show the product is for (NuScience letter).

Link 2: the products are new drugs

Each letter (NuScience letter, Peptide Partners letter) then says the products are new drugs under section 201(p), "because they are not generally recognized as safe and effective (GRASE) for use under the conditions prescribed, recommended, or suggested in their labeling." The statute's own definition of a new drug turns on a drug that "is not generally recognized, among experts qualified by scientific training and experience to evaluate the safety and effectiveness of drugs, as safe and effective for use under the conditions prescribed, recommended, or suggested in the labeling thereof" (21 U.S.C. 321).

Our read: the phrase in their labeling matters for an operator. The conditions FDA measured against are the ones the store's own labeling suggested, and FDA counted the website as labeling, as the next section shows.

Link 3: a new drug needs an approved application

Each letter states the rule: "With certain exceptions not applicable here, a new drug may not be introduced or delivered for introduction into interstate commerce without an approved application from FDA in effect, as described in section 505(a) of the FD&C Act, 21 U.S.C. 355(a)." Then the fact: "No approved applications pursuant to section 505 of the FD&C Act, 21 U.S.C. 355, are in effect for these products." Sources: NuScience letter, Peptide Partners letter.

Link 4: selling them is a violation

The conclusion, again identical in both letters: "The introduction or delivery for introduction into interstate commerce of these unapproved new drug products violates sections 301(d) and 505(a) of the FD&C Act, 21 U.S.C. 331(d) and 355(a)." Sources: NuScience letter, Peptide Partners letter.

Our read: the chain does not depend on purity, a certificate of analysis or a buyer complaint. It depends on intended use, and intended use came from the website.

What does "intended use" mean in these letters?

Both letters tie their evidence to a named regulation. Each introduces the quoted copy as "Examples from your product labeling, including on your website, that provide evidence of the intended use (as defined in 21 CFR 201.128) of these products as drugs." Sources: NuScience letter, Peptide Partners letter.

That regulation, 21 CFR 201.128, says intended use words "refer to the objective intent of the persons legally responsible for the labeling of an article (or their representatives). The intent may be shown by such persons' expressions, the design or composition of the article, or by the circumstances surrounding the distribution of the article. This objective intent may, for example, be shown by labeling claims, advertising matter, or oral or written statements by such persons or their representatives."

The same regulation adds that "Objective intent may be shown, for example, by circumstances in which the article is, with the knowledge of such persons or their representatives, offered or used for a purpose for which it is neither labeled nor advertised," and that "The intended uses of an article may change after it has been introduced into interstate commerce by its manufacturer." Source: 21 CFR 201.128.

Mapped onto the two letters, in our reading, FDA drew on three sources of intent: the store's expressions (the copy it quoted), the circumstances of distribution (the water sold beside the peptides, and in one letter a calculator), and labeling that reaches beyond the vial (the website, and in one letter a linked third party page).

The word objective is the operator's warning. The regulation does not ask what the store owner privately meant. It asks what the store's words and catalog show.

What website statements did FDA quote as proof?

This section delivers outcome 3 of 5: recognize the copy FDA quoted.

This is the part of the letters most worth reading in full. FDA did not summarize the copy. It quoted it, product by product, with the address of each page. Below we quote what FDA quoted, as FDA's evidence, and nothing here is a statement by this site about any compound.

What FDA quoted from NuScience

The NuScience letter quotes at least one passage for each peptide product. Among them, all as quoted by FDA in the NuScience letter:

For GLP-3 RT (Retatrutide) Research Peptide: a product description about a novel investigational peptide and its research applications in metabolic conditions.
For Survodutide: research summary copy about rodent studies of weight and blood sugar.
For Mazdutide: copy that refers to clinical trials, on weight and metabolic topics.
For the Tesamorelin Ipamorelin Blend: copy about visceral fat and the liver for tesamorelin, and copy about bone formation for ipamorelin.
For PT-141 Peptide (Bremelanotide): copy about experimental research on neural control of sexual function. Source: NuScience letter.

One more item in the NuScience letter is easy to miss. For GLP-1 Sema Research Peptide, the passage FDA quoted was not on the store's own domain. FDA cited a page on a public compound database, noting it was "hyperlinked from" the store's product page, and quoted that page's text. Our read: FDA treated a page the store linked to as part of the store's evidence. A link to an outside source is not neutral just because someone else wrote the words. Source: NuScience letter.

What FDA quoted from Peptide Partners

The Peptide Partners letter quotes a different style of copy: short summaries of individual studies, each starting from what a study looked at and ending on what it suggests. Among them, all as quoted by FDA in the Peptide Partners letter:

For GLP-1 S (Semaglutide): a summary of a laboratory study, with a closing line about bone tissue.
For GLP-2 T (Tirzepatide): a summary of a receptor finding, with a closing line about blood sugar and body weight.
For GLP-3 Reta (Retatrutide): a news style summary linking the compound to a type of breast cancer.
For SS-31 (Elamipretide): a lab study summary with a closing line about the retina.
For Tesa Peptide (Tesamorelin): a study summary about liver mechanisms in a patient population.
For PT-141 (Bremelanotide): a passage about receptor binding and sexual function. Source: Peptide Partners letter.

What the quoted copy has in common

Our read, which is judgment drawn from the quotations above:

1. Almost none of it is a direct sales claim. Nothing FDA quoted tells the reader to buy the product for a purpose. Most passages read as research summaries, and FDA quoted them anyway.

2. The subject words carry the weight. In our reading, what made each passage evidence was the condition or body function it named, which is the language of the statutory drug definition FDA cited, not the tone it was written in.

3. Animal and lab framing did not help. Rodent models and laboratory studies are both in the quoted evidence. A cell or rodent setting did not remove the finding.

4. Mentions of human trials sat next to research labels. Our read: copy that refers to trials in people, on a page whose label says the opposite, undercuts the label.

5. Your own word choice is evidence. In the Peptide Partners copy FDA quoted, the store itself called one of its products a drug.

For a wider look at what FDA has cited across peptide sellers, see what FDA warning letters say about peptide marketing. For the evidence question underneath all of this, see preclinical vs human evidence in peptide research.

Did the research use only label change the outcome?

FDA said "evidence obtained from your website establishes that your products are intended to be drugs for human use," despite labels reading "for laboratory, research, and analytical use" and "not intended for human or veterinary use." Source: FDA warning letter to NuScience Peptides LLC.

The Peptide Partners letter says the same thing about a differently worded label: "Despite statements on your product labeling marketing your products 'for research use only' and 'not for human or veterinary use,'" the same website evidence "establishes that your products are intended to be drugs for human use." Source: FDA warning letter to Peptide Partners LLC.

What the two label versions tell you

The two stores used different research wording: one said "for laboratory, research, and analytical use," the other "for research use only." One said "not intended for human or veterinary use," the other "not for human or veterinary use." The outcome was the same. Our read: no particular wording of the disclaimer protected either store. The variable that mattered was the rest of the page. Sources: NuScience letter, Peptide Partners letter.

What else FDA put in the footnote

Each footnote adds one more fact beyond the quoted claims. For NuScience: "In addition to the cited drug claims, you market bacteriostatic water alongside a 'peptide calculator,' a resource that provides the means to prepare an injectable drug for human administration." For Peptide Partners: "In addition to the cited drug claims, you market bacteriostatic water as a solvent for reconstituting your products, thus, providing the means to prepare an injectable drug for human administration." Sources: NuScience letter, Peptide Partners letter.

Our read: a site tool can be evidence of intent. A calculator or a preparation guide on the same site as the products is part of the "circumstances surrounding the distribution" that 21 CFR 201.128 names. For what an RUO label can and cannot do, see research use only peptides meaning and limits.

Why was selling bacteriostatic water cited?

This section delivers outcome 4 of 5: explain why the water was cited.

FDA wrote: "The sale of these products together demonstrates that you intend for your “Bacteriostatic water for Peptides (BAC Water)” to be used in combination for injection." Source: FDA warning letter to NuScience Peptides LLC.

The Peptide Partners letter uses the same sentence for its product: "The sale of these products together demonstrates that you intend for your 'Reconstitution Solution (BAC)' to be used in combination for injection." Both letters then reach the same conclusion: the water itself is a drug. Source: FDA warning letter to Peptide Partners LLC.

The reasoning runs in two steps, and it is worth tracing. The NuScience letter says the company offers the water "for sale to be used to reconstitute the peptide products sold on your website, which are drugs intended for injection." The Peptide Partners letter says the same of "the six above-mentioned products." So the water inherits its status from the peptides it is sold beside. Sources: NuScience letter, Peptide Partners letter.

Our read, which is judgment: renaming the water did not help. The two stores used different names, and each name still said what the water was for. FDA used each store's own name in its finding. In our reading, the catalog decision is not what to call the water. It is whether a solvent sold in the same cart as the peptides tells a reader how the products are meant to be prepared. FDA's answer in both letters was yes.

What does each letter ask the company to do, and by when?

The two letters ask for the same things, in the same words, with only the reference number changed. Sources for every quotation in this section: NuScience letter, Peptide Partners letter.

The demand

"Promptly address the violations described herein without delay, including ensuring that appropriate resources are allocated to fully address the violations and prevent their recurrence." And, in each conclusion: "you are responsible for investigating and determining the root causes of any violations and implementing corrective and preventative measures to ensure future and sustained compliance so that these violations and any others do not occur." Sources: NuScience letter, Peptide Partners letter.

Our read: and any others is the phrase to underline. The letters ask for a fix of the cause, not of the quoted lines.

The deadline and the address

"Send your written response to [email protected] within fifteen (15) business days of receipt of this letter." The clock runs from receipt, not from the letter date. Both letters list the delivery method as "VIA ELECTRONIC MAIL READ/DELIVERY RECEIPT REQUESTED." Sources: NuScience letter, Peptide Partners letter.

A worked example, for illustration only: a letter received on a Monday, with no holiday in the period, reaches fifteen business days on the Friday of the third week after. A holiday or a later receipt date moves the end. Count from your own receipt record, and ask counsel how holidays apply.

What the response must contain

"Include the specific steps you have taken to correct any violations, an explanation of each step being taken to prevent the recurrence of violations, as well as copies of related documentation." And for the subject line: "Identify your response with reference number" followed by the letter's own number, 733652 or 735063. Sources: NuScience letter, Peptide Partners letter.

Each letter also leaves a door open: "If you have information that you believe demonstrates that your products are not in violation of the FD&C Act and FDA regulations, include that information for our consideration." Sources: NuScience letter, Peptide Partners letter.

What happens if the company does not respond adequately

"Failure to adequately address violations may result in regulatory or legal action without further notice including, without limitation, seizure and injunction." Both letters also note: "Please note FDA posts warning letters on www.fda.gov." Our read: the letter is public whether or not the company answers, which means customers, processors and competitors can read the same quotations you just read. Sources: NuScience letter, Peptide Partners letter.

For the step by step response plan, see our guide to how to respond to an FDA warning letter for peptides.

How do the two letters compare?

Side by side, the two letters are one template applied to two stores. Every cell below is quoted or counted from the NuScience letter and the Peptide Partners letter; counts are ours.

| Item | NuScience Peptides LLC | Peptide Partners LLC |

|:--|:--|:--|

| Letter date | August 24, 2026 | August 24, 2026 |

| Reference number | 733652 | 735063 |

| Issuing office | CDER | CDER |

| What FDA reviewed | The company's website, July 2026 | The company's website, July 2026 |

| Products named (our count) | 9 | 7 |

| GLP-named products | 3 (GLP-1, GLP-2, GLP-3 names) | 3 (GLP-1, GLP-2, GLP-3 names) |

| Products only in this letter | Survodutide, Mazdutide, Tesamorelin Ipamorelin Blend | SS-31 (Elamipretide) |

| Water product named | Bacteriostatic water for Peptides (BAC Water) | Reconstitution Solution (BAC) |

| Research label FDA quoted | "for laboratory, research, and analytical use"; "not intended for human or veterinary use" | "for research use only"; "not for human or veterinary use" |

| Style of copy FDA quoted | Product descriptions, plus a linked third party page | Study by study summaries |

| Extra evidence in footnote 1 | Water sold "alongside a 'peptide calculator'" | Water marketed "as a solvent for reconstituting your products" |

| Legal findings | 201(g)(1), 201(p), 505(a), 301(d) | 201(g)(1), 201(p), 505(a), 301(d) |

| Action asked | Root cause, corrective and preventive steps, documentation | Root cause, corrective and preventive steps, documentation |

| Deadline | 15 business days from receipt | 15 business days from receipt |

| Response address | [email protected] | [email protected] |

| Stated consequence | Seizure and injunction, among others | Seizure and injunction, among others |

What they have in common

The legal chain, the label finding, the water finding, the demand, the deadline and the consequence are word for word the same. Both letters (NuScience letter, Peptide Partners letter) also carry the same public health paragraph, that "injectable drug products can pose risks of serious harm to users." Our read: the findings did not turn on anything unusual about either store. They turned on a pattern both stores shared: research labeled products, outcome language on the page, and a solvent in the same catalog. Sources: NuScience letter, Peptide Partners letter.

Were these the only letters FDA sent that day?

No. The site's own tracker data, which is this site's data and not an FDA statement, records five FDA warning letters to peptide sellers with the letter date 2026-08-24, including these two. The same data set holds 11 letters in all, dated 2025-12-08, 2026-03-31, 2026-06-17 and 2026-08-24. The tracker records the product lines of the other August 24 letters as including semaglutide, tirzepatide, retatrutide, SS-31, PT-141 and tesamorelin, each "cited by FDA as unapproved new drugs." You can read every entry, with its FDA link, in the FDA warning letter tracker.

This guide names only the two recipients above. Our read: the overlap in product lines across the same day's letters means these two are not isolated cases.

The tracker's data describes its own method. Its source line reads "FDA warning letters, fda.gov, filtered by search_api_fulltext queries (peptide, research use only, retatrutide, BPC-157, tirzepatide research, semaglutide research, lyophilized, peptides)," and its retrieved date is 2026-10-07. That is the site's own data. Our read: a letter that uses none of those words could be missed by the filter, so treat the tracker as a starting list, not a complete one. See the tracker.

What should a GLP-1 class seller audit on its own site?

This section delivers outcome 5 of 5: run the eight point audit.

Everything in this section is our recommendation, which is judgment, not legal advice. Each item is tied to a specific piece of evidence FDA quoted, so you can see why it is on the list. Sources for the evidence: NuScience letter, Peptide Partners letter, 21 CFR 201.128.

1. Product descriptions

What FDA quoted: descriptions naming metabolic and liver conditions, quoted earlier in this guide (NuScience letter).

What to audit: read every GLP-class product page as FDA would, top to bottom. Mark every condition name, body system, outcome word and reference to people. Our recommendation: a product page should identify the material, not describe a result. If a sentence describes a result, it does not belong on an RUO product page.

2. Study summaries and research sections

What FDA quoted: research summary copy about a laboratory study of semaglutide and bone tissue (Peptide Partners letter).

What to audit: every block that summarizes a paper, a trial or what researchers found. In our reading, the letters show that summarizing research in plain language next to a buy button is how outcome claims get onto a page while sounding scientific. Our recommendation: remove study summaries from product pages. If you keep a literature list, keep it bare (title, journal, year) and away from the cart, and have counsel review whether to keep it at all.

3. Outbound links

What FDA quoted: a third party database page "hyperlinked from" the product page (NuScience letter).

What to audit: every outbound link from a product page, a blog post that links to a product, and any learn more button. Open each target and read it as if you wrote it. Our recommendation: if the target page discusses outcomes or use in people, remove the link.

4. Product names

What FDA quoted: the store's own product names, with Research in the title and GLP numbering, listed as unapproved new drugs.

What to audit: product titles, SKU names and URL slugs. Our read: a name cannot fix a page, and the letters show that a shorthand name does not stop FDA from identifying the compound. Our recommendation: use plain chemical identifiers, and do not rely on naming as protection.

5. Solvents and accessories

What FDA found: "The sale of these products together demonstrates that you intend" the water for the use FDA described (NuScience letter).

What to audit: bacteriostatic water, reconstitution solutions, syringes or anything sold for use with peptides, plus bundles, cross sells and cart suggestion widgets that put them in the same cart. Our recommendation: treat this as a catalog decision for counsel, not a copy edit. Both letters named the water as a drug in its own right.

6. Calculators, preparation guides and tools

What FDA found: water sold "alongside a 'peptide calculator,' a resource that provides the means to prepare an injectable drug for human administration" (NuScience letter).

What to audit: calculators, mixing or reconstitution guides, storage advice written for a user rather than a lab, and FAQ entries about preparing a product. Our recommendation: remove anything on the store's domain that explains how to prepare a product for administration.

7. Labels against pages

What FDA found: the labels limited the products to research; the pages said otherwise, and the pages won.

What to audit: compare the label text and the page text side by side for each product. Our read: a label that says one thing and a page that says the opposite gives FDA the contrast these footnotes describe. Fix the page, then keep the label.

8. Every other channel

What the regulation says: intent may be shown by "the circumstances surrounding the distribution of the article," and by "oral or written statements by such persons or their representatives."

What to audit: emails, social posts, affiliate pages, support replies, community groups you run. Our read, which is judgment: the two letters quote only website evidence, but the regulation they cite is not limited to the website. Apply items 1 to 7 to every place you or someone acting for you talks about the products.

For a page level template, see anatomy of a compliant peptide product page. For the bigger question of whether to carry GLP-1 class products at all, see is it legal to sell retatrutide as a research peptide.

Do these letters matter beyond FDA?

Our read: yes, because a public letter is readable by everyone your store depends on. Stripe's prohibited businesses list, for example, includes "Incorrectly labeled research chemicals" (Stripe, Prohibited and Restricted Businesses). The published pages we hold do not say how any processor reads a warning letter. See our payment processor requirements tool.

How should you track new letters?

FDA publishes these letters itself. Each letter states: "Please note FDA posts warning letters on www.fda.gov." Source: NuScience letter.

A practical way to handle this, which is our recommendation:

1. Check the tracker on a schedule. Open the FDA warning letter tracker monthly, and note its retrieved date. The site's own data lists 2026-10-07 as the date of the current pull.

2. Read each new letter in full, not the summary. The useful parts of these two letters are the quoted product copy and footnote 1. A one line summary does not carry either.

3. Log what FDA quoted, not who received it. For each new letter, write down the product names, the types of copy quoted, any tool or accessory FDA named, and the label wording FDA set aside.

4. Compare the log with your own catalog. If a new letter quotes a kind of copy you also use, treat that as the trigger for an audit, not as news.

Your audit checklist

Work through this for every GLP-class product page and for the store as a whole. Keep the answers in writing with the date.

1. Does any product page name a condition, a body system or an outcome? Compare with the passages FDA quoted from both stores.

2. Does any product page summarize a study, a trial or what researchers found? Peptide Partners' study summaries were quoted one by one.

3. Does any product page mention trials or people? NuScience's mazdutide copy referred to trials in people (NuScience letter).

4. Does any page call your product a drug? Peptide Partners' copy did.

5. Where does every outbound link on a product page go, and what does that page say? FDA quoted a linked third party page.

6. Do you sell bacteriostatic water or any reconstitution solution in the same catalog? Both letters named it as a drug.

7. Do bundles, cross sells or cart suggestions pair the water with peptides? "The sale of these products together" was the finding.

8. Is there a calculator, mixing guide or preparation FAQ anywhere on the domain? The NuScience footnote named a "peptide calculator."

9. Do your labels and your pages say the same thing? In both letters, the page outweighed the label.

10. Are product names doing work the page should do? Research in a title did not change the outcome.

11. Do emails, social posts, affiliates or groups you run repeat any of the above? The regulation counts "oral or written statements."

12. If a letter arrived today, could you document each fix with dated copies? The letters ask for "copies of related documentation."

13. Who checks the tracker, and when did they last check it? Write the name and the date.

Sources for the evidence each item points to: NuScience letter, Peptide Partners letter, 21 CFR 201.128.

Self check

Answer each question before reading its answer. If you miss one, reread the section named after it.

1. How many products did the two letters name, by our count, and how do they split?

16: nine in the NuScience Peptides LLC letter and seven in the Peptide Partners LLC letter. See Which products did FDA name?.

2. Which two sections of the FD&C Act did FDA use to find the products were drugs and new drugs?

Section 201(g)(1) for drugs and section 201(p) for new drugs. See What legal findings did FDA make, in its own words?.

3. Did the research labels change what FDA concluded?

No. Both letters say website evidence established the products were intended to be drugs. See Did the research use only label change the outcome?.

4. Why did FDA name the water each company sold?

Because of what it was sold with: FDA said selling the products together showed the company intended them to be used in combination. See Why was selling bacteriostatic water cited?.

5. How long did each company have to respond, and where?

Fifteen business days of receipt, by email to [email protected]. See What does each letter ask the company to do, and by when?.

6. Have you listed every outbound link from your product pages, with a note on what each target says?

If not, start the audit there. See 3. Outbound links.

What you should have when you finish

A marked up copy of every GLP-class product page, with each condition name, outcome word, study summary and reference to people flagged, and a dated record of what you changed.
A list of every outbound link from product pages, with a note on what each target says and whether you kept it.
A written catalog decision on bacteriostatic water and other solvents, reviewed by counsel, with the reasoning.
A record that calculators, mixing guides and preparation FAQs were removed, or a written reason, reviewed by counsel, for keeping any.
A named owner and a monthly date for checking the FDA warning letter tracker, with a log of what each new letter quoted.
A short response plan in case a letter arrives, including who records the receipt date that starts the fifteen business day clock, based on our guide to responding to an FDA warning letter.

Frequently Asked Questions

Which products did FDA name in the August 24, 2026 letters to NuScience Peptides and Peptide Partners?

Sixteen in total. The NuScience letter names nine, including GLP-1 Sema Research Peptide, GLP-2 Tirz Peptide, GLP-3 RT (Retatrutide) Research Peptide, Survodutide, Mazdutide and its BAC water. The Peptide Partners letter names seven, including GLP-1 S (Semaglutide), GLP-2 T (Tirzepatide), GLP-3 Reta (Retatrutide) and its Reconstitution Solution (BAC).

What law did FDA say the companies violated?

Both letters say the products are drugs under section 201(g)(1), new drugs under section 201(p), and that selling them without an approved application "violates sections 301(d) and 505(a) of the FD&C Act, 21 U.S.C. 331(d) and 355(a)." Sources: NuScience letter, Peptide Partners letter.

Does a "for research use only" label protect a GLP-1 product page?

Not in these letters. Despite labels reading "for research use only" and "not for human or veterinary use," FDA wrote that "evidence obtained from your website establishes that your products are intended to be drugs for human use" (Peptide Partners letter).

Can research summaries on a product page count as drug claims?

In these letters, yes. FDA quoted research style copy, for example research summary copy about rodent studies of weight and blood sugar, as evidence of intended use (NuScience letter).

Why did FDA treat bacteriostatic water as a drug?

Because of what it was sold with. FDA wrote that "The sale of these products together demonstrates" the water was meant "to be used in combination for injection," and concluded the water was a drug (NuScience letter).

How long did FDA give each company to respond?

Each letter says to respond "within fifteen (15) business days of receipt of this letter," by email to [email protected], with the reference number in the subject line (Peptide Partners letter).

Can a calculator or mixing guide on my site be evidence against me?

In the NuScience letter, FDA noted the company marketed bacteriostatic water "alongside a 'peptide calculator,' a resource that provides the means to prepare an injectable drug for human administration" (NuScience letter). Our read: treat any such tool as part of your evidence.

How do I find out when FDA sends a new letter to a peptide seller?

FDA states that it "posts warning letters on www.fda.gov" (NuScience letter). This site's FDA warning letter tracker collects peptide related letters; its own data lists a retrieved date of 2026-10-07.

Related guides

Sources

This guide reports what FDA, Stripe, the eCFR and the Cornell Legal Information Institute published, as captured in October 2026. It is not legal advice for your business.

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