PeptideJournal
Regulatory & Legal14 min read

FDA Warning Letters to Peptide Companies: Analysis

The FDA's warning letter database tells a story about where peptide regulation is heading — and it's not subtle.

The FDA's warning letter database tells a story about where peptide regulation is heading — and it's not subtle. Between December 2024 and early 2026, the agency issued an unprecedented wave of enforcement actions targeting peptide vendors, compounding pharmacies, telehealth platforms, and even brand-name pharmaceutical manufacturers.

This analysis breaks down who got letters, what they were cited for, the patterns that emerge, and what it all means for the peptide industry going forward.

Table of Contents

The Scale of the 2024-2025 Enforcement Surge

To understand what happened, look at the numbers. According to FDA's Jill Furman, speaking at the 2025 Enforcement, Litigation, and Compliance Conference, the agency's Center for Drug Evaluation and Research (CDER) saw a 50% increase in warning letters during fiscal year 2025 compared to the prior year.

Furman described FY 2025 as "a year of change" for her office. That is an understatement. The breakdown of CDER warning letters by category tells the story:

CategoryShare of Warning Letters
GMP violations at manufacturing facilities~35%
Telehealth platforms with misleading claims~22%
Unapproved drugs or misbranding~18%
Other drug quality issues~20%
Clinical research/IRB non-compliance~5%

Peptide-related enforcement fell across nearly all of these categories. Online peptide vendors got hit for selling unapproved drugs. Compounding pharmacies got hit for GMP failures. Telehealth platforms got hit for misleading marketing of compounded peptide products. The FDA was not targeting one weak link in the chain — it was going after the entire supply chain simultaneously.

The September 2025 GLP-1 Crackdown

The single largest enforcement event in peptide history occurred in September 2025.

On September 9, 2025, the FDA began issuing more than 50 warning letters to U.S. and international companies that compound or manufacture GLP-1 drugs — primarily semaglutide (the active ingredient in Ozempic and Wegovy) and tirzepatide (Mounjaro and Zepbound). By September 16, the total exceeded 100 letters, including both warning letters and "untitled" letters to various drugmakers and online prescribing companies.

This was not a routine enforcement action. It was a coordinated initiative by the FDA and the Department of Health and Human Services (HHS) targeting what officials described as misleading advertising in the compounded drug space.

The specific claims the FDA objected to:

  • Calling compounded semaglutide or tirzepatide "generic versions" of FDA-approved GLP-1 drugs
  • Stating that compounded products contain "the same active ingredient" as Ozempic or Wegovy
  • Claiming "clinically proven ingredients" for products that have never been through FDA review
  • Marketing compounded GLP-1s with claims of "real results" or "proven effectiveness" for weight loss

For a full breakdown of compounded vs. brand-name semaglutide, see our comparison guide.

Warning Letters to Research Peptide Vendors

Several online peptide vendors that sell products labeled "for research purposes only" received formal warning letters in late 2024 and 2025. The cases are instructive because they show how the FDA builds its case against companies that hide behind research-use disclaimers.

Summit Research Peptides (December 10, 2024)

The FDA reviewed Summit Research Peptides' website (summitpeptides.shop) in October 2024. The company was selling semaglutide, retatrutide, cagrilintide, tirzepatide, and mazdutide — all labeled for research purposes.

But the company's Facebook page told a different story. Summit had posted about "Enhanced Weight Loss" through the "synergistic effects of Cagrilintide and Semaglutide." The FDA noted that cagrilintide has not been approved by the FDA for any use.

The agency concluded that "evidence obtained from your website establishes that your products are intended to be drugs for human use," regardless of the research-use disclaimer.

Summit was part of a batch of warning letters issued on the same date to Prime Peptides, Swisschems, and Xcel Research — all found selling unapproved GLP-1 products.

Pinnacle Peptides (December 12, 2025)

One year later, Pinnacle Professional Research, doing business as Pinnacle Peptides, received a warning letter after the FDA reviewed its website (pinnaclepeptides.com) in November 2025.

Pinnacle's violations were slightly different — the company was selling selective androgen receptor modulators (SARMs), including S4 Andarine, LGD-4033, and MK-2866. These are not peptides, but the enforcement pattern is identical: unapproved substances marketed under research-use disclaimers, classified by the FDA as unapproved new drugs.

Other Research Vendors (2024)

The December 2024 enforcement wave also hit:

  • Prime Peptides — selling unapproved GLP-1 products online
  • Swisschems — marketing research peptides with implicit therapeutic claims
  • Xcel Research — similar violations to Summit Research
  • USApeptide.com — selling unapproved peptide products

Warning Letters to Compounding Pharmacies and 503B Facilities

The September 2025 wave included dozens of compounding pharmacies and 503B outsourcing facilities. The violations cited in these letters differed from those sent to online vendors:

cGMP Violations. The FDA found numerous current Good Manufacturing Practice failures, including:

  • Missing contemporaneous batch records
  • Incomplete documentation of manufacturing processes
  • Inconsistent procedures across batches
  • Inadequate quality control unit policies

Adverse Drug Reaction (ADR) Reporting Failures. 503B outsourcing facilities are required to report adverse events to the FDA. Multiple facilities had failed to submit ADR reports.

Labeling Violations. Some compounded products did not bear the required label "This is a compounded drug" or "This is a repackaged drug."

Compounding of Unapproved Drug Products. Several facilities were cited for compounding drug products that they were not authorized to compound — including substances that had been placed on the FDA's Category 2 list, meaning they have documented safety concerns and cannot be legally compounded.

Darmerica API Warning (December 2025)

The FDA extended its enforcement upstream in December 2025, issuing a warning letter to Darmerica, an Active Pharmaceutical Ingredient (API) importer and manufacturer. Violations included cGMP failures, distribution of retatrutide to 503A compounding pharmacies, and failure to list all drugs distributed into interstate commerce. This letter signaled that the FDA was going after suppliers, not just end-sellers.

Even Big Pharma Was Not Spared

In a move that generated significant media attention, the FDA sent warning letters to the manufacturers of the very drugs being compounded:

Novo Nordisk (September 9, 2025)

Novo Nordisk, the maker of Ozempic, Wegovy, and Victoza, received a warning letter for promoting its drugs during the Oprah Winfrey television special "Shame, Blame, and the Weight Loss Revolution." The FDA found that the company "promoted these drugs in a manner that failed to present the serious risks in a truthful and nonmisleading manner."

Eli Lilly (September 9, 2025)

Eli Lilly received two warning letters on the same date. The first cited its participation in the same Oprah special, promoting Mounjaro and Zepbound without adequate risk disclosures. The second addressed direct-to-consumer online videos posted on regional news websites that the FDA found misleading.

Hims & Hers Health (September 9, 2025)

Hims & Hers, one of the largest telehealth platforms marketing compounded semaglutide, received a warning letter from CDER for "unlawful sale of unapproved and misbranded drugs to U.S. consumers over the internet." The FDA specifically cited Hims' claims that its compounded products contained "the same active ingredient" as Ozempic and Wegovy.

The fact that the FDA targeted both the brand-name manufacturers and the compounders marketing alternatives sent a clear message: no one in the GLP-1 ecosystem is exempt from advertising rules.

Common Violations: What Gets Flagged

Across hundreds of warning letters, several violation categories appear repeatedly:

1. Unapproved New Drug Marketing (Most Common) Selling or marketing a substance that has not been through the FDA's approval process as safe and effective for any use. This applies to research peptide vendors, clinics prescribing unapproved compounds, and anyone marketing peptides for therapeutic purposes without FDA clearance.

2. Misbranding Products are "misbranded" when their labeling is false or misleading, when they lack adequate directions for use, or when they fail to bear required labeling (like "This is a compounded drug"). This was cited across both research vendors and compounding pharmacies.

3. False and Misleading Claims Specific language triggers this violation: claims of being a "generic version," claims of having the "same active ingredient" as an approved drug, unsubstantiated efficacy claims, and comparative claims that imply equivalence with FDA-approved products.

4. cGMP Manufacturing Violations Manufacturing quality failures accounted for roughly 35% of all warning letters. Missing batch records, inadequate quality testing, and procedural inconsistencies were the most common specific findings.

5. Failure to Report Adverse Events 503B outsourcing facilities have mandatory adverse event reporting obligations. Multiple facilities were cited for failing to report known adverse reactions.

The "Research Use Only" Pattern

One of the clearest patterns in the warning letter data is the FDA's systematic rejection of "research use only" (RUO) disclaimers.

The FDA's position, stated in multiple warning letters, is that when a company sells products that are clearly intended for human use — based on marketing claims, social media posts, product configurations (pre-filled syringes, kits with bacteriostatic water), or customer-facing content — a research-use disclaimer is legally meaningless.

The agency has described these disclaimers as "a ruse to avoid FDA scrutiny" and has used them as evidence of willful non-compliance rather than good-faith attempts at legal protection.

This is consistent across every warning letter reviewed. The FDA looks past the disclaimer and examines the totality of evidence for intended use. If the totality points to human consumption — and it almost always does when peptides are marketed to individuals rather than institutional researchers — the disclaimer provides zero protection.

cGMP Violations: The Manufacturing Problem

The 35% of warning letters citing GMP failures reveal a quality problem in the peptide compounding and manufacturing sector that goes beyond marketing claims.

Common cGMP failures identified in FDA warning letters include:

ViolationDescription
Missing batch recordsNo contemporaneous documentation of manufacturing steps
Inadequate testingInsufficient or absent potency, purity, and sterility testing
Environmental controlsInadequate cleanroom conditions or air quality monitoring
Personnel trainingStaff without documented training in aseptic technique
Equipment calibrationManufacturing equipment not calibrated or maintained per schedule
Stability testingNo data supporting beyond-use dates assigned to products
Deviation managementNo formal process for investigating manufacturing deviations

These are not trivial paperwork issues. When a compounding pharmacy fails to properly test for sterility, patients receive injectable products that may contain bacterial contamination. When potency testing is inadequate, patients may receive doses that are too high or too low. The FDA found that up to 40% of tested online and compounded peptides contained incorrect dosages or undeclared ingredients.

Import Alerts and Supply Chain Enforcement

In September 2025, alongside the warning letter wave, the FDA launched a new enforcement tool: Import Alert 66-80, a "Green List" identifying approved GLP-1 API manufacturers. APIs from manufacturers not on this list face automatic detention at the border.

This followed the earlier expansion of Import Alert 66-78, which in 2025 added 12 additional unapproved peptides to the list of substances subject to detention without physical examination — meaning products are held at customs and denied entry unless the importer can prove they comply with FDA requirements.

The import alert system targets the upstream supply chain. Many compounding pharmacies and online vendors source their raw peptide powders from manufacturers in China, India, and other countries. The Green List creates a checkpoint: if the API manufacturer is not FDA-verified, the raw materials never enter the country.

This is a significant escalation. Previous enforcement focused on the companies selling finished products to consumers. Import alerts attack the supply chain itself.

What Happens After a Warning Letter

A warning letter is not a fine. It's a formal notification that the FDA has identified violations and expects corrective action within 15 working days. Here's the timeline:

  1. Letter issued and publicly posted. Warning letters are published on the FDA's website, making them visible to customers, competitors, and investors.

  2. 15-day response window. The company must submit a written response describing corrective actions taken or planned, or explaining why the FDA's findings are incorrect.

  3. FDA review. The agency evaluates the response for adequacy.

  4. Further action if response is insufficient. Options include:

    • Product seizure
    • Injunctions (court orders to stop specific activities)
    • Civil monetary penalties
    • Criminal prosecution
    • Import bans
    • Debarment from government contracts

  5. Follow-up inspections. The FDA may conduct unannounced inspections to verify that corrective actions were actually implemented.

In practice, many companies that receive warning letters shut down or significantly alter their operations. The public nature of warning letters — combined with the threat of seizure and injunction — creates immediate business consequences even before formal legal action begins.

The September 2025 letters specifically stated that companies "may face legal action without further notice, including seizure or injunction" if violations were not corrected.

Several trends emerge from the 2024-2025 warning letter data:

1. Enforcement is expanding up the supply chain. The Darmerica API warning letter and the Green List import alert show the FDA moving beyond end-sellers to target raw material suppliers. This creates pressure at every level of the peptide supply chain.

2. GLP-1 enforcement is the wedge. While the September 2025 wave focused on semaglutide and tirzepatide, the enforcement infrastructure — import alerts, cGMP inspections, advertising scrutiny — applies to all peptides. GLP-1s are the highest-profile target, but the tools developed for GLP-1 enforcement will be used across the board.

3. Telehealth platforms are a primary target. The 22% of warning letters targeting telehealth platforms reflects the FDA's focus on the distribution model that has made compounded peptides widely accessible. The SAFE Drugs Act of 2025, introduced in Congress, would further expand FDA oversight of telehealth peptide prescribing.

4. "Research use only" is no longer a viable business model. The FDA has systematically dismantled the legal fiction that allows companies to sell human-use peptides under research disclaimers. Companies still operating this model should consider their legal exposure carefully.

5. The enforcement posture may persist regardless of political changes. While the current administration's approach to supplement regulation is evolving, the FDA's peptide enforcement has bipartisan support — driven by patient safety concerns, adverse event reports, and pressure from brand-name manufacturers like Novo Nordisk and Eli Lilly who want to protect their market share.

For the complete FDA regulatory timeline and details on what the compounding crackdown means for consumers, see our regulatory coverage.

FAQ

How many warning letters has the FDA sent to peptide companies?

In FY 2025, the FDA sent more than 100 warning and untitled letters related to GLP-1 peptides alone in September 2025. Additional letters were sent throughout 2024 and 2025 to research peptide vendors, compounding pharmacies, and API suppliers. The exact total is difficult to pin down because the FDA's database categorizes letters by company and violation type, not by product category.

No. A warning letter is a formal notice of violations with a 15-day response deadline. It is not itself a penalty. However, failure to respond adequately can lead to product seizure, injunctions, civil penalties, and criminal prosecution. The public posting of warning letters also creates immediate reputational and financial consequences.

Which peptide companies have received warning letters?

Publicly identified companies include Summit Research Peptides, Prime Peptides, Swisschems, Xcel Research, USApeptide.com, Pinnacle Peptides, Hims & Hers Health, DirectMeds, Novo Nordisk, Eli Lilly, and API supplier Darmerica. The full list of September 2025 recipients exceeds 50 companies and is available through the FDA's warning letters database.

What should consumers take away from these warning letters?

If a company you've purchased from has received an FDA warning letter, it means the agency found evidence of regulatory violations. This does not necessarily mean the products were dangerous, but it does mean the company was not operating within the legal framework. For peptide patients, the safest approach is to work with licensed providers who source from 503A or 503B pharmacies.

Will the FDA continue this level of enforcement in 2026?

The enforcement infrastructure is in place — import alerts, inspection protocols, and inter-agency coordination with the FTC and state attorneys general. Whether enforcement intensity remains at FY 2025 levels depends partly on political factors and partly on whether the industry self-corrects. The FDA has signaled that it views the current enforcement as a baseline, not a peak.

The Bottom Line

The FDA's warning letter campaign of 2024-2025 was not a random burst of enforcement. It was a systematic effort targeting every link in the peptide supply chain — from overseas API manufacturers to domestic compounding pharmacies to telehealth platforms to online research vendors, and even to brand-name pharmaceutical companies.

The message is consistent across every letter: marketing unapproved peptides for human use violates federal law, regardless of disclaimers; compounding pharmacies must meet GMP standards and compound only authorized substances; advertising claims must be truthful and adequately supported; and the FDA is willing to pursue seizure, injunction, and criminal prosecution when corrective action is not taken.

For patients, the takeaway is about sourcing. Peptides that come through legitimate channels — FDA-approved products prescribed by licensed providers, or legally compounded peptides from licensed pharmacies — carry far less risk than products from companies operating outside the regulatory framework. The warning letter database, available at FDA.gov, is a free tool for checking whether a company has been flagged.

For more context on the regulatory environment, see our complete 2025-2026 FDA regulation timeline, the GLP-1 compounding ban, and the state-by-state legal guide.

References

  1. Wilson Sonsini. "FDA Sends Warning Letters to More Than 50 GLP-1 Compounders and Manufacturers." September 2025. https://www.wsgr.com/en/insights/fda-sends-warning-letters-to-more-than-50-glp-1-compounders-and-manufacturers.html

  2. FDA. "Summit Research Peptides Warning Letter 695607." December 10, 2024. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/summit-research-peptides-695607-12102024

  3. FDA. "Pinnacle Professional Research dba Pinnacle Peptides Warning Letter 719337." December 12, 2025. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/pinnacle-professional-research-dba-pinnacle-peptides-719337-12122025

  4. The FDA Group. "CDER Warning Letters Jump 50% in FY 2025 — What That Means for Industry." https://insider.thefdagroup.com/p/cder-warning-letters-jump-50-percent

  5. RAPS. "FDA Posts More Than 100 Warning and Untitled Letters in Ad Crackdown." September 2025. https://www.raps.org/news-and-articles/news-articles/2025/9/fda-posts-more-than-100-warning-and-untitled-lette

  6. STAT News. "FDA Takes on GLP-1 Compounding Boom with Warnings About Misleading Marketing." September 19, 2025. https://www.statnews.com/2025/09/19/fda-obesity-semaglutide-tirzepatide-telehealth-warning-compounding-glp1/

  7. Spencer Fane. "Beyond the Headlines: FDA Warning Letters to GLP-1 Compounders." https://www.spencerfane.com/insight/beyond-the-headlines-fda-warning-letters-to-glp-1-compounders/

  8. Dykema. "Congress Introduces SAFE Drugs Act of 2025, Expanding FDA Oversight of Compounded GLP-1 Drugs and Telehealth Providers." https://www.dykema.com/news-insights/congress-introduces-safe-drugs-act-of-2025-expanding-fda-oversight-of-compounded-glp-1-drugs-and-telehealth-providers.html

  9. MedShadow Foundation. "FDA Drug Recalls and Warnings: Illegal GLP-1 Sales and Misleading Marketing by Novo Nordisk and Eli Lilly." https://medshadow.org/drug-updates-recalls/fda-recalls-and-warnings/fda-drug-recalls-and-warnings-illegal-glp-1-sales-and-misleading-marketing-by-novo-nordisk-and-eli-lilly/

  10. Health Law Alliance. "FDA Targets GLP-1 and Peptide Compounding, Advertising and 'Research Use Only' Labeling." https://www.healthlawalliance.com/blog/fda-targets-glp-1-and-peptide-compounding-advertising-and-research-use-only-labeling

  11. Health Law Alliance. "Darmerica — FDA Issues Warning Letter Targeting GLP-1 API Supply Chain Manufacturer." December 2025. https://www.healthlawalliance.com/blog/darmerica--fda-issues-warning-letter-targeting-glp-1-api-supply-chain-manufacturer

  12. Pharmaceutical Technology. "Lilly, Novo, Hims Get FDA Warnings About Misleading Drug Communications." https://www.pharmtech.com/view/lilly-novo-hims-get-fda-warnings-about-misleading-drug-communications

  13. Frier Levitt. "Regulatory Status of Peptide Compounding in 2025." https://www.frierlevitt.com/articles/regulatory-status-of-peptide-compounding-in-2025/

  14. FDA. "FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss." https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss

  15. Partnership for Safe Medicines. "September 8, 2025: FDA Launches an Import Alert Listing Safe GLP-1 Manufacturers." https://www.safemedicines.org/2025/09/sept-8-2025.html