The US Food and Drug Administration has issued five warning letters to online peptide sellers, according to a report by Pharmaceutical Technology, all of them centered on unapproved weight-loss and fat-reducing compounds. The named companies are Peak Performance Peptides, Royal Peptides, NuScience Peptides, Peptide Partners and TXP Innovations LLC dba Tex Peptides.

The letters detail violations of FDA regulations covering the sale of new peptide-based drugs that remain unapproved and unregulated. All five sites were flagged for advertising their own versions of retatrutide, Eli Lilly's obesity candidate, which has not secured approval in any global market.

The retatrutide problem

Retatrutide is the clearest case here because there is no legitimate consumer version of it anywhere on earth. Lilly itself sounded the alarm on the drug's growing black market shortly before this, as some patients look for cheaper alternatives to branded weight-loss medicines.

All five companies are also offering illegal variations of semaglutide, Novo Nordisk's GLP-1 receptor agonist sold in the US as Wegovy for obesity and Ozempic for type 2 diabetes. That is the pattern regulators keep finding: the compound with the biggest waiting list attracts the biggest gray market.

Not just weight loss

The rosters go well beyond obesity drugs, into growth hormone release-stimulating, muscle-boosting and libido-enhancing products. Pharmaceutical Technology lists copycat versions of Theratechnologies' abdominal fat-reducing Egrifta (tesamorelin), Mighty Therapeutics' Barth syndrome drug Forzinity (elamipretide) and Cosette Pharmaceuticals' Vyleesi (bremelanotide) for hypoactive sexual desire disorder.

The research-use-only defense

Every site reviewed sells these peptides under a research-only label, stating they are "not for veterinary or human use." The FDA refutes that, saying evidence from each website establishes the products are intended for human use.

The letters also flag the dangers of unregulated injectables, which the agency says "can pose risks of serious harm to users" because they enter the bloodstream directly and bypass the body's natural defenses against toxins and pathogens. That is the part of this story with actual stakes, and it is independent of whether any given molecule works.

Two directions at once

The timing is odd. While the FDA sends warning letters, its advisory board recently voted to relax peptide restrictions, potentially allowing specialized pharmacies to supply multiple peptides without full clinical testing.

Karsten Eastman, CEO of regulated peptide developer Sethera, told Pharmaceutical Technology there is a dire need for greater public clarity around peptides and their potential. On current evidence, he is not wrong.