In the post-Iran-Iraq War era, Iran’s defense and security policymakers have increasingly prioritized expanding military power, particularly through missile development strategies. Since then, the Islamic Republic of Iran has consistently considered missiles a legitimate tool for self-defense. In ongoing confrontations between Iran and the United States, preventing the advancement of Iran’s defensive capabilities has been a significant challenge for U.S. foreign policy. Consequently, the U.S. has employed various strategies to limit and halt Iran’s missile program, including the implementation of secondary sanctions by Congress. These sanctions intensified in 2012 and continued until the Joint Comprehensive Plan of Action (JCPOA) was established. Most secondary sanctions were suspended after the JCPOA agreement but were reimposed with greater intensity following the U.S.’s unilateral withdrawal from the JCPOA in 2018 under President Trump. This study addresses the main question: What impact have U.S. Congressional secondary sanctions had on the missile defense program of the Islamic Republic of Iran? The research employs a qualitative method involving thematic analysis, gathering information through interviews. Thematic analysis of the data yielded four primary themes: restrictions on access to technology, increased costs, restrictions on access to expert workforce, and the localization of missile technology to enhance deterrent capability. According to the experts in this study, these themes are the most critical factors influenced by U.S. Congressional secondary sanctions on Iran’s missile defense program.