How to Respond to an FDA Warning Letter for Peptides

You have 15 business days to email a written response to [email protected], with the letter's reference number in the subject line. That is the instruction in two of FDA's August 24, 2026 warning letters to peptide sellers, which also ask for the corrective steps taken, how recurrence will be prevented and copies of supporting documents.

To see which letters FDA has sent to peptide sellers and what each cited, use the FDA warning letter tracker.

This guide is a working response plan for founders and operators of research use only (RUO) peptide stores. It is built from what FDA itself asked of the recipients of two letters dated August 24, 2026, one to NuScience Peptides LLC and one to Peptide Partners LLC. It covers every action those letters ask for, the laws they cite, the evidence FDA used, a worked 15 business day plan, an outline for the response letter and a checklist. Every quotation is copied from its source. Every timeline that is not quoted from FDA is a worked example, and is labeled as one.

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What you will be able to do after reading

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

1. Work out your deadline, when the clock starts, and where the response goes. Delivered in How long do you have to respond to an FDA warning letter?.

2. List every action the letter asks of you, and explain why the letter is not a complete list. Delivered in What does an FDA warning letter ask you to do?.

3. Name the five kinds of evidence FDA treated as proof of intended use. Delivered in What did FDA treat as evidence of intended use?.

4. Run a worked 15 business day plan and draft an eight section response letter. Delivered in A 15 business day response plan and What should the response letter contain?.

5. Decide what to document and keep, and when to bring in an attorney. Delivered in What should you document and keep? and When should you bring in an attorney?.

The self check near the end tests each one.

Key Facts

• Deadline: "within fifteen (15) business days of receipt of this letter," in the words of both letters (NuScience letter, Peptide Partners letter).
• Where: email [email protected] with the letter's reference number in the subject line. The two reference numbers were 733652 and 735063.
• What: the corrective steps taken, how recurrence will be stopped, and copies of supporting documents.
• Scope: each letter says it "is not intended to be an all-inclusive list of the violations that may exist in connection with your products or operations."
• Root cause: FDA puts it on the recipient: "you are responsible for investigating and determining the root causes of any violations."
• Consequence: "Failure to adequately address violations may result in regulatory or legal action without further notice including, without limitation, seizure and injunction."
• Evidence FDA used: statements on the sellers' own product pages, a page hyperlinked from a product page, and the sale of bacteriostatic water alongside the peptides.
• Labels did not settle it: FDA wrote that despite "for research use only" style statements, "evidence obtained from your website establishes that your products are intended to be drugs for human use" (Peptide Partners letter).
• Publicity: "Please note FDA posts warning letters on www.fda.gov."

How long do you have to respond to an FDA warning letter?

This section delivers outcome 1 of 5: work out your deadline and address.

You answer in writing, by email, within 15 business days. Two of FDA's August 24, 2026 letters to peptide sellers, to NuScience Peptides LLC and Peptide Partners LLC, give the same instruction: "Send your written response to [email protected] within fifteen (15) business days of receipt of this letter." They add: "Identify your response with reference number" from the letter "in the subject line of the email." Sources: FDA warning letter to NuScience Peptides LLC, FDA warning letter to Peptide Partners LLC.

When does the clock start?

The letters count from "receipt of this letter." Both were sent the same way: "Delivery Method: VIA ELECTRONIC MAIL READ/DELIVERY RECEIPT REQUESTED" (NuScience letter). So the letter arrives in an inbox, and FDA asked for a read or delivery receipt. The letters do not define a business day, and they do not say whether receipt means the moment the email arrived or the moment it was opened.

A practical way to handle this: treat the day the email arrived as day zero. If it landed in a spam folder or an unread shared inbox, do not assume the clock waited for you. Record the arrival time from the email header, and ask counsel how to count the days.

Can you get more time?

The published letters do not say. Neither mentions an extension or a partial response. Our reading: plan a complete response inside the window, and raise any need for more time with your attorney before the deadline.

Where is the address, and what is the reference number?

The address is in the letter: "Send your written response to [email protected]" (Peptide Partners letter). The reference number is printed at the top of each letter, as "Reference Number: 733652" for NuScience Peptides LLC and "Reference Number: 735063" for Peptide Partners LLC, and the closing tells the recipient to "Identify your response with reference number" in the subject line (NuScience letter).

Our recommendation for the subject line: put the reference number first, then your legal entity name, then the words Response to Warning Letter. A worked example, for a hypothetical letter numbered 000000: 000000, Example Store LLC, Response to Warning Letter dated, followed by the letter date. Use the number on your own letter, never one from this page.

What does an FDA warning letter ask you to do?

This section delivers outcome 2 of 5: list every action the letter asks for.

More than write back. Read both letters line by line and by our count, they ask the recipient to do seven distinct things. Here is each one, in FDA's words, from the NuScience Peptides LLC letter; the Peptide Partners LLC letter uses the same sentences.

1. Act now. "Promptly address the violations described herein without delay, including ensuring that appropriate resources are allocated to fully address the violations and prevent their recurrence."

2. Own compliance across the business. "It is your responsibility to ensure that your firm complies with all requirements of federal law, including FDA regulations."

3. Find the root cause. "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."

4. Respond in writing, on time. "Send your written response to [email protected] within fifteen (15) business days of receipt of this letter."

5. Show the steps. "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."

6. Label the email. "Identify your response with reference number" from the letter "in the subject line of the email."

7. Make your case, if you have one. "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."

Notice the tense in item 5. FDA asks for "steps you have taken," past tense, and an explanation of each step "being taken" to prevent recurrence. In our reading, a response that only promises future work answers half the sentence. The strongest answer shows changes already live on the day you send it, with documents that prove them.

Why the letter is not a complete list

Each letter says so twice. Near the top: "This is not intended to be an all-inclusive list of the violations that may exist in connection with your products or operations." And again, before the violations: "As a reminder, this is not an all-inclusive list of violations that may exist in connection with your products or operations" (Peptide Partners letter).

The operator lesson is direct. Fixing only the product pages FDA named is the minimum, not the job. In our reading, the same kind of language left on an uncited page is a hole FDA told you about in advance. Audit the whole catalog, every linked page, and every channel you sell or advertise through.

What happens if you do not fix the violations?

FDA says it in one sentence, near the top of each letter: "Failure to adequately address violations may result in regulatory or legal action without further notice including, without limitation, seizure and injunction." Source: FDA warning letter to NuScience Peptides LLC.

Three phrases in that sentence matter for planning. Adequately means a response that exists is not the same as a response that is enough. Without further notice means you should not expect a second letter before any action. Without limitation means seizure and injunction are examples, not the full list. The letters do not say what FDA would do first, or when.

There is a second consequence that does not depend on what you send. The letters close with: "Please note FDA posts warning letters on www.fda.gov." Both letters are public pages, and the NuScience page shows "Content current as of: 09/01/2026" (NuScience letter). Our reading: assume customers, processors and partners can read your letter. Plan what you will say to them while you plan what you will say to FDA.

Which laws does FDA cite in these letters?

By our count, the letters build a chain of four legal steps. You need to understand each link, because a response that disagrees with FDA has to break one of them, and a response that agrees has to show the facts behind each one have changed. Source for every quote in this section: FDA warning letter to NuScience Peptides LLC, with the same text in the Peptide Partners LLC letter.

Link 1: the products are drugs

In the NuScience letter, the 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."

That section is the statutory drug definition. The text of 21 U.S.C. 321 covers "articles recognized in the official United States Pharmacopoeia, official Homoeopathic Pharmacopoeia of the United States, or official National Formulary, or any supplement to any of them," and "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." It also covers "articles intended for use as a component of any article specified in clause (A), (B), or (C)."

The operative word for a store is "intended." The statute defines a drug partly by what it is intended for, not only by what is in the vial. That is why the letters spend most of their length on the sellers' own words.

Link 2: intended use is shown by what you say and how you sell

FDA tied its evidence to a regulation by name: "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" (NuScience letter).

The regulation, 21 CFR 201.128, says intended use refers 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."

It adds two sentences an operator should read slowly. "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: "The intended uses of an article may change after it has been introduced into interstate commerce by its manufacturer." Source: 21 CFR 201.128.

In our reading, this is the reason a response cannot stop at the product page. Advertising matter, written statements and the circumstances of distribution all count. Your emails, ads, social posts, support replies and what you sell together are part of the record.

The statute's definition of labeling is broad too. 21 U.S.C. 321 defines labeling as "all labels and other written, printed, or graphic matter (1) upon any article or any of its containers or wrappers, or (2) accompanying such article." And FDA's letters describe the evidence as "product labeling, including on your website" (NuScience letter, Peptide Partners letter).

Link 3: they are new drugs without approval

The products "are 'new drugs' under section 201(p) of the FD&C Act, 21 U.S.C. 321(p), because they are not generally recognized as safe and effective (GRASE) for use under the conditions prescribed, recommended, or suggested in their labeling." Then: "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)." And: "No approved applications pursuant to section 505 of the FD&C Act, 21 U.S.C. 355, are in effect for these products." Source: NuScience letter.

Note the phrase "in their labeling" again. The new drug step also runs through what the labeling prescribes, recommends or suggests.

Link 4: shipping them is the violation

"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)." Both letters came from the "Center for Drug Evaluation and Research (CDER)." The statute defines interstate commerce as "commerce between any State or Territory and any place outside thereof," among other things (21 U.S.C. 321, NuScience letter).

In our reading, the violation FDA named is shipping. Editing a page changes the evidence going forward, not what already shipped, which is why counsel should decide what your response says about past orders, stock and continued sales.

What did FDA treat as evidence of intended use?

This section delivers outcome 3 of 5: name the five kinds of evidence.

The website, almost entirely. Each letter opens: "This warning letter advises you of significant violations observed during a U.S. Food and Drug Administration (FDA) review of your website." It then says "Violations were identified and documented during a review of your website" in July 2026 (Peptide Partners letter). Neither letter describes an inspection, a test purchase or a lab test. Your response is answering a reading of your own pages.

By our count, five kinds of evidence appear in the two letters. Each one maps to a corrective step.

1. Product page copy written in research language

FDA quoted product descriptions that were framed as research summaries. In the NuScience letter, FDA quoted copy describing animal study work on one compound, and copy on another product page calling a compound an investigational peptide under study for metabolic conditions (NuScience letter). That is our description of the type of copy, not the sellers' words.

The operator lesson: words like "research," "rodent models" and "preclinical" did not keep the copy out of the letter. FDA quoted it as evidence of intended use anyway. When you audit, read for whether a sentence ties the product to an outcome rather than to a laboratory property, not for whether it sounds scientific.

2. Summaries of studies placed on product pages

The Peptide Partners letter quoted study summaries on product pages, cut down with ellipses. FDA quoted research summary copy about a bone study, and a line about research on a different compound's activity in the body, both placed on product pages (Peptide Partners letter). Those are our descriptions of the type of copy, not the sellers' words.

Our reading: a study summary on a page where the product is for sale is treated as part of what you say about the product. If your pages carry study digests, citations with commentary, or what the research shows sections, they belong in the audit.

3. Pages you link to

The NuScience letter quoted text "On the webpage" of a third party database, which it described as "hyperlinked from" the seller's product page for one product (NuScience letter).

That is a concrete instruction for your audit. Follow every outbound link on every product page and read the destination as if you had written it. FDA did.

4. What you sell together

Both letters treated bacteriostatic water as a drug because of what it was sold with. From the Peptide Partners letter: "Your firm offers 'Reconstitution Solution (BAC)' for sale to be used to reconstitute the peptide products sold on your website, which are drugs intended for injection." Then: "The sale of these products together demonstrates that you intend for your 'Reconstitution Solution (BAC)' to be used in combination for injection. Therefore, your 'Reconstitution Solution (BAC)' is a drug." The NuScience letter makes the same finding about its "Bacteriostatic water for Peptides (BAC Water)" (NuScience letter, Peptide Partners letter).

Both letters also explain why FDA singled out injectables: "These products are especially concerning from a public health perspective because injectable drug products can pose risks of serious harm to users" (NuScience letter, Peptide Partners letter).

5. Tools on your site

The NuScience letter's footnote adds: "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." The Peptide Partners footnote says the firm marketed "bacteriostatic water as a solvent for reconstituting your products, thus, providing the means to prepare an injectable drug for human administration" (NuScience letter, Peptide Partners letter).

Our reading: calculators, preparation guides and similar tools are not neutral site features in FDA's eyes. They are part of the circumstances of distribution.

What the research use label did and did not do

Both letters address the disclaimer head on. NuScience Peptides LLC marketed its products "for laboratory, research, and analytical use" and "not intended for human or veterinary use." Peptide Partners LLC marketed its products "for research use only" and "not for human or veterinary use." In both cases FDA wrote: "evidence obtained from your website establishes that your products are intended to be drugs for human use" (NuScience letter, Peptide Partners letter).

So a response that leans on the disclaimer is arguing a point FDA already rejected in writing. Our recommendation: keep accurate research use statements, but do not present them in your response as the fix. The fix is removing the evidence FDA cited and the evidence like it. For what research use only labeling means and where it stops, see research use only peptides meaning and limits.

A 15 business day response plan

This section delivers outcome 4 of 5: run the 15 business day plan.

The plan below is a worked example, not FDA guidance. FDA sets only the endpoint: a written response "within fifteen (15) business days of receipt of this letter" (NuScience letter). The day numbers, task order and buffer are our own judgment, built so that each task maps to something the letter asks for. Adjust it with your attorney.

Week one: preserve, stop, inventory

Day 1. Record and preserve. Save the letter email with full headers and note when it arrived. Save the letter as a PDF. Before you change anything, capture every page FDA quoted, plus every product page, linked page and tool page on the site, with date stamped screenshots and saved page files. Name one person who owns the response. Call your attorney. This day serves the root cause duty: you cannot investigate what you erased.

Day 2. Map the letter. Build a table with one row per product FDA named and one row per quoted statement, with the URL FDA cited. Add a column for each of the seven asks listed earlier in this guide. Every later task should fill a cell in this table.

Day 3. Decide on sales of cited products. With counsel, decide whether to pause the cited products, take their pages down, or both, and what happens to open orders. The letter's chain ends at shipping, so this is the decision with the most weight. Write the decision down with its date and who made it.

Day 4. Take down or rewrite cited content. Remove every statement FDA quoted. Remove or rework the linked pages, study summaries and tools FDA cited. Capture the after state of each page the same way you captured the before state.

Day 5. Inventory every channel. List every place the business says anything about its products: product and category pages, blog and FAQ pages, email flows, ad accounts, marketplace listings, social profiles, affiliate pages, inserts and support macros. The regulation names "advertising matter, or oral or written statements," so a list limited to the website is too short (21 CFR 201.128).

Week two: audit and find the cause

Days 6 and 7. Audit the whole catalog. The letter is "not an all-inclusive list," so read every product and every channel from day 5 against the five kinds of evidence above. Flag any sentence that ties a product to an outcome rather than a laboratory property, any study summary, any outbound link, any product sold as a companion to another, and any preparation tool. Fix as you go and log each fix.

Day 8. Bundles and companions. Review what is sold together, cross sold, recommended at checkout or bundled. Both letters turned a companion product into a drug finding. Decide with counsel what stays.

Day 9. Root cause. Write down how the cited content got there. Who wrote it, who approved it, what template or supplier copy it came from, what review step was missing. FDA asked you to determine "the root causes of any violations," so the answer should name process failures, not just pages (Peptide Partners letter).

Day 10. Controls. Write the controls that answer each root cause: a claims policy, an approval step before anything goes live, a ban list, an outbound link rule, a review cycle for old content, training and a named owner. Put them into effect, and date them.

Week three: assemble, review, send

Day 11. Build the exhibits. For every corrective step, collect the proof: before and after captures, change logs, the written policy, training records, the decision record on sales. Number each exhibit.

Day 12. Draft the letter. Use the outline in the next section. Each corrective step points to an exhibit number.

Day 13. Counsel review and live check. Your attorney reviews the draft. Someone who did not make the changes opens every URL in the response and confirms the live page matches what it says.

Day 14. Send. Send to the address in the letter, with the reference number in the subject line. Keep the sent email, the attachments as sent, and any delivery confirmation.

Day 15. Buffer. In this worked example the last day is spare, kept for a failed attachment or a late fix.

What should the response letter contain?

This outline is our judgment, not an FDA template. FDA did not publish a required format in these letters. Each section below is tied to a sentence FDA did write, from the NuScience Peptides LLC letter.

Section 1: identification

Your legal entity name, the reference number, the letter date, and the person responsible for the response. This answers "Identify your response with reference number."

Section 2: summary of what you have done

A short paragraph stating what changed and when: products removed from sale, pages taken down or rewritten, tools removed, with dates. This answers "Promptly address the violations described herein without delay."

Section 3: product by product corrections

One subsection per product FDA named, in the order the letter lists them. For each one: the statement FDA quoted, the URL, what you did, the date, and the exhibit that proves it. Include companion products such as bacteriostatic water and any tool the footnote named. This answers "Include the specific steps you have taken to correct any violations."

Section 4: beyond the letter

What you found and fixed that FDA did not cite, across the catalog and every channel. This answers the warning that the letter is "not an all-inclusive list" and the duty that "these violations and any others do not occur."

Section 5: root cause

What allowed the content to be published. Name the process gap. This answers "you are responsible for investigating and determining the root causes of any violations."

Section 6: preventive controls

Each control, the date it took effect, who owns it, and how it is checked. This answers "an explanation of each step being taken to prevent the recurrence of violations."

Section 7: information for FDA's consideration, if any

If counsel believes some product or statement is not in violation, the evidence goes here, kept separate from the corrections. This answers "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." Our recommendation: keep argument out of the corrections sections.

Section 8: exhibit index

A numbered list of every attached document. This answers "copies of related documentation."

What to leave out

Our recommendation: leave out claims you cannot prove with an exhibit, undated promises, statements about what your products do, and arguments resting only on the research use label. You are writing a record, not a rebuttal.

What should you document and keep?

This section delivers outcome 5 of 5: decide what to document and keep.

FDA asked for "copies of related documentation," so the documents are part of the response, not a side task (Peptide Partners letter). Our recommended file, built as a judgment from what the letters ask for:

• The letter itself, the original email with headers, and your note of when it arrived.
• Before captures of every page FDA quoted and every page you changed, with dates and URLs.
• After captures of the same pages, showing the change live, with dates.
• A change log: one row per change, with the URL, what was removed or rewritten, who did it and when.
• The sales decision record for cited products: what was paused, from when, and what happened to open orders and stock.
• The channel inventory from day 5, with the status of each channel.
• The root cause write up.
• The written controls: the claims policy, the approval workflow, the link rule, the ban list, the content review cycle.
• Training records: who was trained on the new policy, and when.
• The response as sent, every attachment, and any delivery confirmation.
• Everything after: any reply from FDA, and every later content change, logged the same way.

Our reading: keep the before captures even though they show the problem. They are what proves the change happened.

What do the FTC statutes say about advertising claims?

FDA wrote these two letters, but federal advertising law sits next to the same words. The Federal Trade Commission Act section on false advertisements, 15 U.S.C. 52, says: "It shall be unlawful for any person, partnership, or corporation to disseminate, or cause to be disseminated, any false advertisement." It covers advertising "By United States mails, or in or having an effect upon commerce, by any means, for the purpose of inducing," or "which is likely to induce, directly or indirectly the purchase of food, drugs, devices, services, or cosmetics." It adds: "The dissemination or the causing to be disseminated of any false advertisement within the provisions of subsection (a) of this section shall be an unfair or deceptive act or practice in or affecting commerce within the meaning of section 45 of this title."

The definitions section, 15 U.S.C. 55, defines a false advertisement as one that "means an advertisement, other than labeling, which is misleading in a material respect." In judging that, the statute takes into account "but also the extent to which the advertisement fails to reveal facts material in the light of such representations or material with respect to consequences which may result from the use of the commodity." Its drug definition uses the same wording as the FD&C Act: "articles intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease in man or other animals" and articles "intended to affect the structure or any function of the body of man or other animals."

What this means for your response, in our reading:

• The FTC definition excludes labeling, while the FDA letters cite labeling. Cover both: product pages for FDA, and ads, emails, social posts and affiliate content as advertising.
• Cause to be disseminated reaches content others publish for you, such as affiliate pages and reseller listings.
• Fails to reveal facts material means removing a claim is safer than qualifying it.
• Our sources hold no FTC action against either letter recipient. The point is only that the words FDA cited are the kind of words these statutes address.

For a wider view of what FDA has cited in peptide sellers' copy, see what FDA warning letters say about peptide marketing.

When should you bring in an attorney?

On day 1. Our recommendation is not to draft a word of the response before regulatory counsel has read the letter. The letters name statutes, cite a regulation by number, end the legal chain at the act of shipping and warn of "seizure and injunction" (NuScience letter). That is legal exposure, and the response is a written record you cannot take back.

Decisions in this plan that, in our judgment, need counsel rather than an operator alone:

• Whether to pause or stop sales of cited products, and what to do with stock and open orders.
• Whether any part of the letter should be answered with "information for our consideration," and how.
• How to describe past sales in the response, if at all.
• How to count the 15 business days.
• What to say to customers and partners once the letter is public.

For how to choose one and what to ask, see peptide business attorney: when you need one.

How does the warning letter tracker help?

The FDA warning letter tracker is this site's own data, not an FDA product. For each letter it records the recipient, the letter date, the FDA URL, a short description of the products or practices cited, and an evidence quote taken from the letter. The data gives its source as "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 lists a retrieved date of 2026-10-07. Its letters range from December 2025 to August 2026.

Three uses, in our judgment:

1. Pattern check. Read what FDA cited in other letters to peptide sellers, then search your catalog for the same products, names and statements.

2. Wording check. The evidence quotes are FDA's own extracts. A phrase on your page that reads like one is a finding.

3. Monitoring. After you respond, check the tracker on a schedule as part of your review cycle.

The tracker is a snapshot, so open the FDA page itself before relying on any detail.

What if you believe FDA is wrong?

The letters leave room for that: "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." Source: FDA warning letter to NuScience Peptides LLC.

Our reading: the sentence asks for information, not argument, and it does not suspend the rest of the letter. The same letter still asks for corrective steps, root cause and prevention. A response that only disputes, with no corrections, leaves most of FDA's asks unanswered. Whether and how to dispute is a decision for counsel.

Response checklist

Work through this list before you send. Each line ties to something the NuScience Peptides LLC letter or the Peptide Partners LLC letter asks for, or to a judgment we have labeled above.

1. Have you recorded when the letter arrived, and counted 15 business days from it with counsel?

2. Did you capture every cited page before changing it?

3. Is every statement FDA quoted gone from the live site, and have you checked each URL yourself?

4. Have you reviewed outbound links, calculators, companion products, bundles and cross sells, including bacteriostatic water?

5. Have you audited every product and every channel, not only the ones FDA named?

6. Have you inventoried ads, emails, social, affiliates and support macros as advertising matter?

7. Has counsel decided, in writing, what happens to sales of cited products?

8. Have you written a root cause that names process gaps?

9. Are your preventive controls written, dated, owned and already in effect?

10. Does every corrective step in the letter point to a numbered exhibit?

11. Is any disagreement kept in its own section, as information for FDA's consideration?

12. Is the reference number in the subject line, and is the email going to the address printed in your letter?

13. Is the response going out with at least one business day to spare?

14. Have you planned what to tell customers and partners, since FDA posts letters publicly?

Self check

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

1. How long do you have to respond, and from when does the time run?

Fifteen business days from receipt of the letter. See When does the clock start?.

2. Where does the response go, and what must the subject line carry?

An email to [email protected], with the letter's reference number in the subject line. See Where is the address, and what is the reference number?.

3. Which three things must the response give FDA?

The corrective steps taken, how recurrence will be stopped, and copies of supporting documents. See What does an FDA warning letter ask you to do?.

4. Is the list of violations in the letter complete, and who must find the root cause?

The letter says it is not an all inclusive list, and FDA puts the root cause investigation on the recipient. See Why the letter is not a complete list.

5. Name three kinds of evidence FDA used in the August 2026 letters.

Statements on the sellers' own product pages, a page hyperlinked from a product page, and the sale of bacteriostatic water alongside the peptides. See What did FDA treat as evidence of intended use?.

6. Do you have a numbered exhibit set ready to attach?

If not, build it from the exhibit index before you send. See Section 8: exhibit index.

What you should have when you finish

• A sent response, with the reference number in the subject line, delivered inside 15 business days, and a saved copy with every attachment.
• A live site where none of the statements FDA quoted remain, and where the same kinds of statements are gone from every other page.
• A numbered exhibit set: before and after captures, a change log, the sales decision record, the root cause write up, the written controls and the training records.
• A written claims policy with an approval step, a link rule and a named owner, already in effect.
• A monitoring routine that includes checking the FDA warning letter tracker and re auditing old content on a schedule.
• A standing relationship with regulatory counsel.

Frequently Asked Questions

How many days do you have to respond to an FDA warning letter?

The two August 24, 2026 letters to peptide sellers ask for a written response "within fifteen (15) business days of receipt of this letter" (NuScience letter). They do not define a business day, so confirm the count with counsel.

Where do you send the response?

By email to the address in the letter. Both letters say "Send your written response to [email protected]" and ask you to put the letter's reference number in the subject line (Peptide Partners letter).

What does FDA want in the response?

"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." FDA also expects you to determine root causes (NuScience letter).

Is it enough to fix only the pages FDA quoted?

No. Each letter says it "is not intended to be an all-inclusive list of the violations that may exist in connection with your products or operations," and asks for measures so that "these violations and any others do not occur" (NuScience letter).

Does a research use only label protect the products?

Not in these letters. Despite research use statements on the labeling, FDA wrote that "evidence obtained from your website establishes that your products are intended to be drugs for human use" (Peptide Partners letter).

Why was bacteriostatic water cited as a drug?

Because of what it was sold with. FDA wrote that "The sale of these products together demonstrates that you intend for your 'Reconstitution Solution (BAC)' to be used in combination for injection" (Peptide Partners letter).

What happens if you ignore the letter?

FDA wrote: "Failure to adequately address violations may result in regulatory or legal action without further notice including, without limitation, seizure and injunction" (NuScience letter).

Can you disagree with FDA in the response?

Yes, with evidence. The letters say: "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" (NuScience letter). Decide that with counsel.

What can this guide not tell you?

Our sources are the two letters, the statutes and the regulation they cite, the federal advertising statutes, and this site's tracker data. They do not say how FDA evaluates a response, how long a review takes, whether extensions are granted, how business days are counted, or when a letter is closed out. Those are questions for regulatory counsel.

Related guides

• Two FDA Warning Letters on GLP-1 Research Peptides, 2026
• What FDA Warning Letters Say About Peptide Marketing: 2026 Update
• Peptide Business Attorney: When You Need One
• Anatomy of a Compliant Peptide Product Page
• Research Use Only Peptides Meaning and Limits

Sources

• U.S. Food and Drug Administration, Warning Letter to NuScience Peptides LLC, reference 733652, August 24, 2026. Read October 8, 2026, captured again October 25, 2026.
• U.S. Food and Drug Administration, Warning Letter to Peptide Partners LLC, reference 735063, August 24, 2026. Read October 8, 2026, captured again October 25, 2026.
• United States Code, 21 U.S.C. 321, Definitions. Read October 8, 2026.
• Code of Federal Regulations, 21 CFR 201.128, Meaning of "intended uses". Read October 8, 2026.
• United States Code, 15 U.S.C. 52, Dissemination of false advertisements. Read October 8, 2026.
• United States Code, 15 U.S.C. 55, Additional definitions. Read October 8, 2026.
• Peptide Ecommerce, FDA warning letter tracker. Site's own data, retrieved date 2026-10-07.

This guide reports what FDA, the cited U.S. Code and Code of Federal Regulations text, and this site's own tracker published or recorded, as captured on October 8, 2026 and October 25, 2026. It is not legal advice for your business.