The first post in this series ended with the molecule. Semaglutide represented the current apex of a decades-long engineering effort to take a two-minute gut hormone and turn it into a once-weekly drug — and the structural logic behind that transformation was reasonably well understood. What it did …

For most of the twentieth century, the drugs we reached for to treat obesity worked the way a sledgehammer works: broadly, imprecisely, and often destructively. It took decades of failures — and a detour through lizard venom — to understand that the body already had a system for regulating weight, …