League of Nations, International Opium Convention (1968)
“ The Contracting Powers who have post-offices in China shall adopt efficacious measures to prohibit the illegal importation into China, in the guise of a postal package, as well as the illegal transmission from one locality to another in China through the intermediary of these post-offices, of opium, whether raw or prepared, of morphine and of cocaine and their respective salts, and of other substances indicated in article 14 of the present Convention. ”
