Academy of Medical Sciences of I.R. Iran Archives of Iranian Medicine 1029-2977 23 11 2020 11 01 Fifty Years of Research and One Conclusion: Opium Causes Cancer 757 760 10.34172/aim.2020.95 EN Mahdi Sheikh Farin Kamangar Reza Malekzadeh Journal Article 10.34172/aim.2020.95 2020 10 08 2020 10 14 In September 2020, the International Agency for Research on Cancer (IARC) announced that opium consumption causes cancer in humans – a conclusion drawn after reviewing data from five decades of research. Given the widespread use of opium and its derivatives by millions of people across the world, the classification of opium consumption as a "Group 1" carcinogen has important public health ramifications. In this mini-review, we offer a short history of opium use in humans and briefly review the body of research that led to the classification of opium consumption as carcinogenic. We also discuss possible mechanisms of opium’s carcinogenicity and potential avenues for future research.