Quack medicines were prepackaged, commercially marketed medicinal concoctions brewed from “secret recipes” that often contained powerful drugs. Governmental regulation of them in late nineteenth-century England is heralded as a landmark of public health policy. We argue that it’s instead a landmark of medicinal rent-seeking. We develop a theory of quack medicine regulation in Victorian England according to which health professionals faced growing competition from close substitutes: quack medicine vendors. To protect their rents, health professionals organized, lobbied, and won laws granting them a monopoly over the sale of “poisonous” medicaments, most notably, quack medicines.