The FDA has delivered another clear warning to the peptide and compounding industry. On September 1, 2026, the agency's warning-letter database recorded a new batch of 12 warning letters, covering everything from unapproved peptide drugs and pharmaceutical manufacturing violations to foreign-supplier verification failures. Among the recipients were several companies marketing peptides such as retatrutide and other investigational compounds. At the same time, the FDA has made its position on two of the most closely watched metabolic compounds particularly clear: Retatrutide and cagrilintide cannot be used in compounding under federal law. The agency states that neither compound is an active ingredient in an FDA-approved drug, and neither has been established as safe and effective for any condition. For the research-peptide industry, this distinction matters enormously. The latest enforcement activity is not simply about whether a website uses the words "research use only." It is about how products are marketed, what claims are made, whether the overall presentation establishes an intended use as a drug, and whether products are being introduced into interstate commerce in violation of the Federal Food, Drug, and Cosmetic Act. The September 1 Warning-Letter Batch The FDA's warning-letter database shows 12 letters associated with September 1, 2026. They covered several different regulatory categories. The recipients included: - Peak Performance Peptides - Royal Peptides LLC - NuScience Peptides LLC - Peptide Partners LLC - TXP Innovations LLC, doing business as Tex Peptides - PReye, LLC - Reliance Life Sciences Private Limited - Jabil Inc. - Shoolin Pharma Chem LLP - Fresenius Medical Care AG & Co. KGaA - Mesquite Gourmet LLC - B&P Mutual Corp The FDA categorized five of the letters as unapproved new drugs/misbranding, four as CGMP-related pharmaceutical manufacturing violations, two as Foreign Supplier Verification Program violations, and one as a combination of CGMP/adulteration and unapproved-new-drug violations.