Now, the clamor over unregulated peptides is fueling a high-stakes policy battle within the federal government. Some peptides, such as insulin, human growth hormone and glucagon-like peptide-1, have delivered transformational therapeutic effects when administered to humans. For MOTS-c and a raft of other peptides widely available online, no comparable evidence exists. While many users take multiple peptides together in custom combinations, or “stacks,” there is no data on how different synthetic peptides interact with one another. To date, most of these popular peptides have been available solely in unregulated online marketplaces.