The United States’ withdrawal from the Joint Comprehensive Plan of Action (JCPOA) in 2018 and the reimposition of sanctions led Iran to expand its cooperation with non-Western institutions and partners. Nevertheless, membership in or cooperation agreements with such institutions do not necessarily entail effective access to economic benefits or a reduction in the effects of sanctions. This study aims to examine the pathologies of Iran’s multilateral policy in the post-JCPOA period through a comparison of the perceptual and operational environments. The central question is: What pathologies has Iran’s multilateral policy encountered in the post-JCPOA era? The study argues that the pathologies of Iran’s multilateral policy stem not only from limitations in the instruments of cooperation, but also from miscalculations regarding the capacity of these instruments, the extent of partners’ commitments, and the conditions under which the benefits expected from cooperation can be realized. Using a comparative case-study design, the study examines Iran’s participation in the Shanghai Cooperation Organisation (SCO) and BRICS, as well as its trade engagement with the Eurasian Economic Union (EAEU), from May 2018 to December 2025. The findings identify four main patterns of pathology in Iran’s multilateral policy: a formalistic understanding of institutional cooperation; the predominance of security and geopolitical considerations over economic assessment; the substitution of symbolic indicators for performance measures; and the overestimation of institutional capacity and partners’ commitments. The cross-case comparison also demonstrates that formal status, the possibility of cooperation, and realized benefits must be distinguished from one another.