Matt Kaeberlein, a longevity researcher, first started hearing about peptides a few years ago. “At that point it was mostly functional medicine doctors that were using peptides,” he says, referring to physicians who embrace alternative medicine and supplements. “In the last six months, it’s kind of gone crazy.”

Peptides have gone mainstream. At the health-technology startup Superpower in Los Angeles, employees can get free peptide shots on Fridays. At a health food store in Phoenix, a sidewalk sign reads, “We have peptides!” At a tae kwon do center in South Carolina, a peptide wholesaler hosts an informational evening. On social media, they’re everywhere. And that popularity seems poised to grow; Department of Health and Human Services secretary Robert F. Kennedy Jr. has promised to end the FDA’s “aggressive suppression” of peptides.

The benefits and risks of many of these compounds, however, are largely unknown. Some of the most popular peptides have never been tested in human trials. They are sold for research purposes, not human consumption. Some are illegal knockoffs of wildly successful weight-loss medicines. The vast majority come from China, a fact that has some legislators worried. Last week, Senator Tom Cotton urged the head of the FDA to crack down on illegal shipments of peptides from China. In the absence of regulatory oversight, some people are sending the compounds they purchase off for independent testing just to ensure that the product is legit. 

What is a peptide?

A peptide is simply a short string of amino acids, the building blocks of proteins. “Scientists generally think of peptides as very small protein fragments, but we don’t really have a precise cutoff between a peptide and a protein,” says Paul Knoepfler, a stem-cell researcher at the University of California, Davis. Insulin is a peptide, as is human growth hormone. So are some neurotransmitters, like oxytocin. 

But when wellness influencers talk about peptides, they’re often referring to particular compounds—formulated as injections, pills, or nasal sprays—that have become trendy lately. 

Some of these peptides are FDA-approved prescription medications. GLP-1 medicines, for example, are approved to treat diabetes and obesity but are also easily accessible online to almost anyone who wants to use them. Many sites sell microdoses of GLP-1s with claims that they can “support longevity,” reduce cognitive decline, or curb inflammation.