With the popularity of GLP-1s skyrocketing, the “P,” which stands for peptides, is having its own moment. Peptides are naturally occurring chains of amino acids that send signals to our bodies to perform important processes. They regulate the immune system, grow cells, reduce inflammation, manage hormones and more. Bodybuilders trying to boost their muscle mass and biohackers seeking to optimize their health and longevity have used synthetic peptides for years.