Rhubarb has a laxative effect. In the 19th century, China exported rhubarb to Britain for this very purpose: Britain, for her part, was flooding China with opium – which shows a marked disparity between the philanthropic intentions of the two countries. When the outbreak of the First Opium War looked inevitable, the Chinese Commissioner, Lin Tse-Hsü, believing that the British would die of constipation en masse if deprived of rhubarb, threatened to halt the export of the vegetable. For unknown reasons, Queen Victoria apparently never had the letter translated so we will never know if rhubarb could have prevented the Opium Wars.
I have heard that the smoking of opium is very strictly forbidden by your country; that is because the harm caused by opium is clearly understood. Since it is not permitted to do harm to your own country, then even less should you let it be passed on to the harm of other countries – how much less to China! Of all that China exports to foreign countries, there is not a single thing which is not beneficial to people: they are of benefit when eaten, or of benefit when used, or of benefit when resold: all are beneficial… Take tea and rhubarb, for example; the foreign countries cannot get along for a single day without them. If China cuts off these benefits with no sympathy for those who are to suffer, then what can the barbarians rely upon to keep themselves alive?
(Lin Tse-Hsü – Letter of Advice to Queen Victoria 1839)