USC Davis School of Gerontology

A few months ago, Pinkas Cohen of a thriving online trade in MOTS-C, a peptide that, when injected into mice, seems to mimic the effects of exercise.

The dean of the USC Leonard Davis School of Gerontology was very familiar with this particular short chain of amino acids.

His lab identified it years ago as one of the thousands of peptides that act as chemical messengers in the human body, one he believed might someday have therapeutic uses for humans.

But Cohen was alarmed to learn that his discovery was now being promoted by legions of longevity seekers, fitness enthusiasts, and wellness influencers as...