The health secretary has advocated for deregulating certain peptides, but FDA scientists point to a lack of data about their safety and effectiveness. Some haven’t been studied in humans.

Peptides are molecules made up of chains of amino acids, the building blocks of proteins. Thousands are found naturally in the body but they can also be made synthetically in a lab.

They’ve seen a recent surge in popularity as wellness influencers and popular podcasters have touted them for weight loss and as remedies for injuries, joint pain and myriad other issues. Kennedy has said he’s used peptides on injuries with “really good effect.”

But they exist largely in a “gray market”: They’re not FDA-approved drugs, but they can be found online from unregulated suppliers. In April, Kennedy reclassified 12 peptides as Category 1 substances, the first step toward adding them to a list of substances that compounding pharmacies can make. (Compounding pharmacies make customized versions of medications that aren’t available at standard pharmacies.) Kennedy said at a House hearing that month that the Biden administration had incorrectly flagged the peptides as posing safety risks.