Peptide Products Flood Market, But Neuroscientists Say Evidence Lags Behind Claims

Peptides — short chains of amino acids that the body uses to carry signals related to hunger, stress, pain, sleep and mood — have become a staple of consumer advertising, promising younger-looking skin, relief from joint pain, weight loss and treatment for a long list of other conditions. The pitches appear on television, online and across social media.

But neuroscientists caution that many of these claims are not backed by the evidence. Nikki Crowley, an associate professor of biology and director of the Penn State Neuroscience Institute, said researchers remain enthusiastic about peptides as potential therapies, even as she urged consumers to treat bold marketing promises with skepticism.

"The peptide industry feels a little bit like the Renaissance version of the supplement industry," Crowley said, recalling how consumers were exposed to a wave of supplements in the 1990s and 2000s that were later found to be unsafe or ineffective. She suggested applying the same caution to peptides being marketed today.

Crowley explained that peptides are the body's communication molecules, carrying messages about states such as hunger, stress and pain, as well as more complex conditions like mood and social interaction. Scientists have long been interested in their therapeutic potential for cognition and a range of disorders, and research in animals has produced strong evidence that peptides could be good targets for conditions including Alzheimer's disease, cognitive decline, addiction, anxiety, depression and mood disorders.

A major obstacle, however, is the blood-brain barrier — a strict gatekeeper that regulates what enters the brain. While the body's own signals need to reach the brain, the barrier evolved to keep out foreign substances such as viruses, and it is reluctant to admit injected drugs or peptides. That means promising laboratory and animal findings do not automatically translate into a workable treatment.

The arrival of GLP-1 targeting drugs for diabetes and obesity has renewed scientific interest in peptides as druggable targets, Crowley noted, and the ability to deliver peptides into the brain is an area of intense interest. But she stressed that laboratory evidence only shows how a molecule might work, not that it does so safely and effectively in people.

"For that, you really want to see that gold standard clinical trial," she said, adding that the bolder the claim, the higher the bar for evidence should be. For many peptides marketed for cognition, mood or working memory, she said, the underlying neuroscience is not nearly as advanced as the advertisements suggest.