Peptides: What they are and how they work

Four small vials of injectable peptides. — (Image credit: Future)

What are peptides?

These short chains of amino acids are found naturally in the body and act as useful messengers, telling cells when to repair damaged tissue, produce hormones, reduce inflammation, and more. Scientists have turned a number of peptides into safe and effective drugs, including insulin, which moves sugar from blood into cells, and GLP-1 (the P stands for peptide), which helps regulate appetite and is used in weight-loss medications such as Ozempic. But a growing number of Americans are now taking peptides that, unlike those drugs, haven’t undergone a rigorous testing and approval process.

Administered via self-injection, these chemicals are claimed to result in thicker hair, increased libido, greater muscle mass, better skin, heightened focus, and more. Their seemingly miraculous properties have been praised by tech CEOs, podcaster Joe Rogan, and celebrities such as Gwyneth Paltrow, Jennifer Aniston, and Kim Kardashian, who says her daily regimen “changed my life.” But many doctors are alarmed by a craze that has thousands of people injecting themselves with substances of dubious origin and whose long-term effects are unknown. “It’s unfounded and reckless,” said Eric Topol, director of the Scripps Research Translational Institute.

Investors believe it’s a $1-billion-to-$3-billion-a-year market, but hard figures are elusive, because most peptides are sold on the quasi-legal gray market. Some are prescribed by doctors and dispensed by compounding pharmacies, which produce tailored medications. Others, which are legal to buy but not approved for use in humans, are sourced from Chinese labs and labeled “for research purposes only.” According to U.S. customs data, imports of Chinese hormone and peptide compounds hit $328 million in the first nine months of 2025, double the total for the same period of 2024. The wild success of GLP-1 drugs, which raised awareness of peptides, has partly fueled the boom, along with growing interest among the wealthy in biohacking—using regimens and supplements to improve the body’s performance and longevity— and glowing testimonials from social media influencers and peptide converts. “I hear it all day, every day: ‘This changed my life,’” said Amanda Kahn, a New York City–based doctor nicknamed the “peptide princess.”

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For a legion of reasons. Proponents of GHK-Cu, a peptide found in human plasma, say it boosts collagen production and improves hair and skin. NAD+, touted by Paltrow as “one of my biggest wellness tools,” is claimed to benefit energy levels and memory. Many peptide fans talk about the makeup of their “stack,” or regimen of daily shots. Combine BPC-157 and TB-500 and you get the Rogan-touted “Wolverine stack,” named after the self-healing Marvel Comics mutant superhero. Iván Pol, a celebrity facialist, says a daily stack including GHK-Cu and BPC-157 has raised his energy, dropped his cholesterol, and lowered his body fat. Hassan Sleiman, a 45-year-old roofing contractor in Michigan, claims a regimen of seven peptides has eased body pains and boosted his vitality. At the University of California, Santa Barbara, says 22-year-old student Ryan Roberts, “everybody does them.” The long-term health risks of this experimentation are not yet known, but doctors are worried about higher cancer risk.

A recent study by University of Utah researchers found BPC-157 could promote the growth of tumor cells; TB-500 has been shown to speed tumor growth in lab animals. Doctors note that none of these peptides have scientifically proven benefits. People taking them are “becoming lab rats,” said Adam Taylor, a professor of anatomy at Lancaster University in the U.K. Users, even enthusiastic ones, have reported side effects including hair loss, blurred vision, rashes, and dizziness; two women who got peptide injections at an antiaging festival in Las Vegas last year were hospitalized with swollen tongues, elevated heart rates, and breathing trouble. Adding to doctors’ worries are concerns about purity and dosing, because users typically buy from websites selling unregulated Chinese product— some of which comes from plants that previously produced the deadly opioid fentanyl. Irregularities and contamination are common. Still, one high-profile peptide enthusiast wants to make it easier to get peptides: Health Secretary Robert F. Kennedy Jr.

A self-declared “big fan” of peptides, he has pledged to end their “aggressive suppression” by the FDA. Under former president Joe Biden, the agency classified 19 peptides as unsafe and barred compounding pharmacies from producing and selling them. Later this month, an FDA advisory panel will meet to discuss seven of the chemicals, including those in the Wolverine stack, and issue recommendations. Since at least seven of the panel’s 14 members have ties to the peptide industry or clinics promoting them, it’s expected they’ll advise removing the restrictions—even though FDA scientists in June recommended against doing so, citing insufficient evidence on the peptides’ effectiveness and safety.

It will likely set off a multibillion-dollar gold rush among potential sellers. Among those poised to profit is the San Francisco-based telehealth firm Hims & Hers Health, which last year acquired a peptide-manufacturing facility in Menlo Park, Calif.; the company’s stock price spiked nearly 50% in April in anticipation of possible FDA action. Kennedy and other proponents say removing the restrictions will boost production at reliable, FDA-inspected facilities and open the door to the research critics say is lacking. But critics fear the FDA’s stamp of approval will simply legitimize the use of unproven substances whose dangers may only become apparent in coming years. “We’re all holding our breath a little bit,” said Peter Koshland, who teaches clinical pharmacy at UC San Francisco, “and just hoping that nobody gets hurt.”