Seirogan, a popular anti-diarrhoeal pill, is arguably one of the most successful pharmaceutical products of modern Japan. What is less known is that the Japanese army initially developed Seirogan during the Russo-Japanese War as the ‘Conquer-Russia-Pill’, which was later marketed to the public by private manufacturers. Previous scholars have emphasised the top–down governmental method of mobilising private sectors to manipulate public opinion for the cause of external imperialist expansion and domestic stability during wartime Japan. But the matrix that the Conquer-Russia-Pill allows us to glimpse is an inverted power relation among the state, commercial sectors, and imperial citizens. While the Japanese government remained indifferent if not hostile to jingoistic pharmaceutical manufacturers who could easily disrupt international relations, pharmaceutical companies quickly recognised and exploited the opportunities that the Conquer-Russia-Pill and its symbolism provided under the banner of the empire. In turn, Japanese consumers reacted to commercial sermons carefully anchored in patriotic and militaristic discourses and images by opening their wallets. In other words, the popularity of the Conquer-Russia-Pill was a culmination of the convergence of a governmental initiative to enhance military capabilities, the commercial ingenuity of pharmaceutical manufacturers, and a consumer response to patriotic exhortations.