By MATTHEW PERRONE

WASHINGTON (AP) — Unapproved peptide drugs have become a trendy new hack among wellness influencers , fitness coaches and celebrities, pitched as a way to build muscle, shed pounds and look younger.

Online stores will offer injectable vials for $300 to $600 each. Longevity and wellness clinics offer in-office evaluations and injections, sometimes with membership fees of thousands of dollars per month.

But many of the products have never been extensively studied in humans, raising concerns that they could cause allergic reactions, metabolic problems and other dangerous side effects.

Here’s a closer look at the science, the hype and the potential risks surrounding the trend.

What are peptides?

Within the human body, peptides are short chains of amino acids that

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