In a widely expected move, a committee organized by the Food and Drug Administration (FDA) has voted to endorse removing restrictions on the manufacture of peptides for human use. Thursday’s panel meeting saw a sharply divided group recommend lifting limits on four peptides; votes on three additional peptides are scheduled for today. The move comes despite a continuing lack of evidence regarding their safety and effectiveness.

The move had been telegraphed months earlier as peptide enthusiast and Health and Human Services Secretary Robert F. Kennedy Jr. took steps to ensure this outcome.

Like proteins, peptides are composed of amino acids that are chemically linked into a chain. Peptides differ merely by length; they’re often 10–20 amino acids long, in contrast to proteins, which can be hundreds or thousands. Some of them, such as insulin, are specifically made by targeted processing of a protein into shorter fragments, and the resulting peptide interacts with receptors that have evolved to send signals to cells based on its levels.

But a lot of peptides are just the result of the messy complexity of biology, where larger proteins may break down in a way that consistently produces a stereotypical pattern of fragments. Some of those fragments, being relatively short and flexible, may stick to other proteins in ways that trigger some sort of physiological response. Others may simply be digested and recycled without doing anything of note.

Understanding how a peptide is made and what downstream effects it triggers can take decades of research. In many cases, we have some evidence of what happens when we expose cultured cells to a peptide, but lack any indication of what might happen if an intact animal is. (Notably, transiting this same evidentiary gap is often where promising-looking drug candidates turn into failed ones.)