Sources: U.S. Food and Drug Administration (FDA) Compounding and the FDA (503A & 503B guidance) FDA warning letters on unapproved peptide products National Institutes of Health (NIH) PubMed The FDA has issued warning letters to multiple companies marketing compounded Retatrutide, an investigational drug from Eli Lilly still in Phase II trials. While early studies have shown promising weight loss results, Retatrutide BPC 157: Experimental Peptide Creates Risk for Athletes The U.S. Food and Drug Administration is moving toward allowing compounding pharmacies to produce more than a dozen injectable peptides that were banned because of potentially significant safety risks, the New York Unauthorized injectable peptide drugs seized and sold by Canada Peptide may pose serious health risks Canada.ca