Across the US, thousands of people are injecting themselves with unregulated peptides in pursuit of weight loss, muscle growth and younger-looking skin. Despite being labelled 'not for human consumption', the substances are readily available online and have surged in popularity among people disillusioned by traditional healthcare. To find out why so many Americans are willing to risk unknown side-effects for the promise of a quick fix, Adam Gabbatt meets the users and influencers driving the peptide boom, and investigates what's really inside some of these so-called 'miracle' drugs