Merchants of Medicines reinterprets the long-distance medicine trade as an economic and political project essential to empire. Systems of exchange, plantation agriculture, military fiscalism, and healthcare developed together on a global scale from the late seventeenth century to the era of Atlantic revolutions. Questions of how and why they did so, and with what consequences for a range of people organize the book. It follows medicines from their manufacture in Britain, across trade routes, and to the edges of empire, along the way telling a story of what medicines were, what they did, and what they meant. The narrative encompasses London laboratories, Caribbean estates, South Asian factories, and New England timber camps to recover how the production, distribution, and consumption of manufactured medicines linked those systems. Medicines offered the prospect of health and wealth, while underwriting the gendered and racialized regimes at the core of commercial empires. They also reshaped the ways people understood themselves, their neighbors, and the world around them. By bringing together histories of capitalism, empire, medicine, and science, Merchants of Medicines offers a new history of economic and medical development across early America, Britain, and South Asia, revealing the unsettlingly close ties among medicine, finance, warfare, and slavery that shaped the course of healthcare and political economy.