By MATTHEW PERRONE, Associated Press Health Writer

Associated Press (AP) — More Americans are injecting themselves with unapproved chemicals that are pitched as ways to build muscle, rejuvenate skin and extend life, the latest example of the nation’s fascination with alternative therapies and wellness hacks.

Behind the trend is the surging popularity of GLP-1 weight loss medications, a class of so-called peptides approved to help users quickly shed pounds.

But the peptides being promoted by influencers, celebrities and wellness gurus are different: Many have never been approved for human use and much of their purported evidence comes from studies in rats and other animals. Several peptides, such as BPC-157 and TB-500, are banned by international sports authorities as doping substances.

“None of them are proven,” said Dr. Eric Topol, a research methods expert and director of Scripps Research Translational Institute. “None of them have gone through what would be considered adequate clinical trials, but nonetheless many people are taking these. It’s actually quite extraordinary.”

Those who’ve highlighted peptides’ benefits include Health Secretary Robert F. Kennedy Jr., who has built a national following among Americans who are deeply skeptical of health experts, pharmaceutical companies and traditional medicine.

For years, the Food and Drug Administration has been trying to crack down on the space, sending warning letters to clinics that promote the products and adding more than two dozen peptides to a list of ingredients that should not be made by specialty pharmacies that often custom mix the formulations.

That approach may be coming to an end.

Kennedy has vowed to end “FDA’s war” on peptides and other alternative treatments that are embraced by many in his Make America Healthy Again movement.

Some of Kennedy’s friends and associates are among the biggest proponents, including self-described “biohacker” and “longevity expert” Gary Brecka, who sells peptide injectables, patches and nasal sprays through his website for $350 to $600 each.

In a May appearance on Brecka’s podcast, Kennedy again promised to “end the war at FDA” on peptides, stem cells, psychedelics and other fringe therapies.

“Music to my ears,” Brecka replied.

Brecka declined to be interviewed for