This study surveys a century of commercial opium production in Iran, from 1850 to 1955. From an insignificant contributor to the global opium market, Iran became within a few decades an important exporter, turning to the market between 5-10% of the entire global production of opium. Opium-poppy cultivation and opium production formed part of a larger process of transition within the agricultural sector to cash-crop production. Under the growing pressure of increasing imports of European manufactured goods and the collapse of the local manual industries, the production of cash-crops, and particularly opium, was intended to balance Iran's trade deficit. The combination of timely political changes in China, technological improvements in steamboat navigation and a high-quality product, enabled the successful integration of Iranian opium within the global opium market. This success stands in contrast to the usual negative evaluation of Iran's social and economic reforms during the later 19th-century. Parallel to the rise of opium production, opium consumption -- particularly opium smoking -- became very popular in Iran. The extent of this phenomenon caused concern among the country's political and cultural leadership, but the proponents of the anti-opium cause in Iran were never zealots, nor did they wield the sort of political power that matched the influence of anti-opium organizations in the US, Europe and China. Iran was early to join the diplomatic efforts to end the opium trade in the 20th century, but it did so mostly in order to reject or postpone resolutions that would harm the Government's substantial opium revenues. In the end, the economic compensation that came with the larger share in the oil revenues, which Iran negotiated in 1954, and not internal political pressure by anti-opium groups, enabled Iran to forego its opium trade altogether.