Before 1974 controls over Turkey's opium production were ineffective and provided opportunities for large-scale diversion, making it one of the world's largest sources of illicit opium. The state monopoly was limited by a lack of authority over opium producing areas, laissez faire controls and poor state procurement practices. Policies administered between 1933 and 1971 did, however, represent a period of organisational learning which led to the establishment of a highly successful drug control policy. A secondary finding of this paper, revealed whilst analysing diversion estimates, suggests that there may be inaccuracies in assumptions of geographical displacement from Turkey. While these assumptions have been reproduced in much of the literature, the data suggests that the Turkish opium ban of 1971 had either minimal impact on global or regional production levels, or that displacement occurred during the 1960s rather than the mid-1970.