It is not possible to clearly or definitively distinguish the effect of sanctions on Iran from the effect of other policy tools that have been employed. Debate Over Achievements of Sanctions

There has been substantial debate over the degree to which sanctions have contributed to altering Iranian policies—particularly regarding Iran's willingness to negotiate limits to its nuclear program. This debate has been affected significantly by the "Joint Plan of Action" (JPA) agreed on November 24, 2013, between Iran and the P5+1. The agreement, implementation of which began on January 20, 2014, requires Iran to halt further development of most aspects of its nuclear program in exchange for a modest and temporary easing of multilateral sanctions. On the other hand, some experts assert that Iran's signing of the JPA was attributable less to sanctions and more to Iran's perceptions of U.S. flexibility—in particular an apparent U.S. willingness to accept some long-term enrichment of uranium by Iran and pursue overall U.S.-Iran rapprochement. Improving Human Rights Practices . According to the Administration, "If Iran fails to meet its commitments, [the United States and its partners] will revoke the relief." The interim agreement does not require an easing of any U.S. sanctions that were imposed in the 1980s and 1990s primarily to address Iran's support for acts of international terrorism, or any sanctions that address Iran's alleged human rights abuses or its influence in neighboring countries. The Way Forward: Potential Scenarios for Iran Sanctions23

For the duration of the JPA period, international sanctions on Iran are likely to remain in a state of ambiguity—no international sanctions have been lifted or repealed, but many sanctions imposed by individual states are, at least temporarily, relaxed. The future course of Iran sanctions will almost certainly depend, at least in part, on the outcome of the ongoing P5+1 – Iran negotiations for a final settlement on Iran's nuclear program. If the Parties Reach a Comprehensive Nuclear Settlement

The text of the JPA states that a comprehensive solution on Iran's nuclear program "would produce the comprehensive lifting of all UN Security Council sanctions, as well as multilateral and national sanctions related to Iran's nuclear program." With respect to the JPA commitment not to impose new nuclear sanctions during the JPA period, the document states that "The U.S. Administration, acting consistent with the respective roles of the President and the Congress, will refrain from imposing new nuclear related sanctions." We are in agreement with our partners in the P5+1 and the EU [European Union] and with Iran that any sanctions relief, should we get to a comprehensive agreement, will be phased in and will be in response to actions that Iran takes. That lifting some sanctions would require congressional action raises the issue of congressional responses to any comprehensive deal that is reached. There are potential consequences should Congress not lift nuclear-related sanctions after a comprehensive deal. If Negotiations Collapse

Iran sanctions are likely to pursue a far different course if negotiations on a comprehensive nuclear settlement collapse. It can be argued that partner countries would likely support increased sanctions if the collapse of negotiations were widely attributed to Iranian refusal to agree to what were perceived by partner countries as reasonable demands for a comprehensive nuclear settlement. An extension of the JPA has several potential implications for the course of Iran sanctions. The Administration has indicated that such an extension would apply to all provisions of the JPA, including the modest sanctions relief that could provide additional resources to the Iranian government. Congress might seek to enact additional sanctions, such as those included in H.R. There is potential for any of these groups, with or without the knowledge or involvement of Iran, to conduct a catastrophic attack in the Middle East or elsewhere. A related possibility is an attack in the United States by Iran or Iranian proxies, against U.S. or partner interests. According to this view, Iran-supported militants might seek to prevent Iran from potentially abandoning its commitment to militant causes in the region. Resurgence of a Popular Uprising in Iran . A shift in international views on sanctions could result from an Iranian decision to undertake direct military action in the region.
Most experts agree that the multilateral sanctions imposed on Iran since 2010 have contributed significantly to producing flexibility in Iran's position on the scope of its nuclear program. There is similar agreement that the effect of sanctions on Iran's foreign policy—particularly on its core interests in the Middle East region—and on its human rights practices, appear to have been minimal to date. In assessing effectiveness, however, it is difficult to separate the effect of sanctions from other variables such as Iran's purported economic mismanagement, attitudes of the Iranian public, and Iranian politics.
Interim Nuclear Deal of 2013
Sanctions have been eased temporarily under an interim nuclear deal of November 2013 ("Joint Plan of Action," JPA), which included a commitment from the United States to impose no new nuclear-related sanctions for the JPA period (until July 20, 2014). Virtually any next step in U.S. and multilateral sanctions on Iran is likely to depend on the course of negotiations for a comprehensive agreement on Iran's nuclear program. Opinion in the United States on the future course of Iran sanctions is deeply divided. As Congress has been an active proponent of sanctions on Iran for many years, it will remain keenly interested in the future direction of Iran sanctions policy.
Proponents of Additional Sanctions
While negotiations on a comprehensive nuclear settlement are going on, some assert that additional sanctions would reinforce the pressure that appears to have encouraged Iran to accept the JPA and increase Iranian willingness to reach an acceptable permanent settlement. Proponents of increased sanctions maintain that additional sanctions will also prevent an erosion of existing sanctions caused by a perception that the JPA has ended Iran's international isolation.
Critics of Additional Sanctions
Critics of this approach maintain that additional sanctions imposed while comprehensive nuclear settlement talks are in progress would reinforce hardliners in Iran who oppose a nuclear agreement with the United States out of distrust of U.S. intentions. Adding sanctions could also cause U.S. partners to separate their Iran policies from those of the United States—particularly if there is a collapse in the negotiations that appears to stem from what others consider to be excessive U.S. demands. Alternatively, a failure of negotiations that is attributed to Iran's unwillingness to accept seemingly reasonable offers would likely lead to a broad international increase in sanctions on Iran.
The Joint Plan of Action and Additional Future Possibilities
The JPA commits the Administration and its negotiating partners to lifting "nuclear-related sanctions" on Iran if there is a comprehensive nuclear deal. Because of the substantial overlap between nuclear related sanctions and those imposed primarily because of other issues, in practice that represents a commitment to broad sanctions relief. Those who support that commitment maintain that Iran will not have the incentive to agree to a permanent settlement unless there is the prospect of substantial sanctions relief. Critics of this view argue that broad sanctions relief will provide Iran even more resources with which it can support militant movements that oppose U.S. interests in the Middle East, and will not likely compel Iran to conform to international standards of human rights practices.
The future course of Iran sanctions could also be affected by Iranian actions that are unrelated to the nuclear talks. Such actions might include a crackdown against any new popular unrest in Iran, a catastrophic terrorist attack by one of Iran's regional allies, expanded Iranian military intervention in Syria, or a power shift in Iran back toward opponents of a nuclear settlement.
Underlying these debates is a lack of consensus over what would constitute an acceptable final nuclear settlement. On the nuclear issues, some argue that any settlement must result in full dismantlement of Iran's nuclear program. The Administration has indicated in the JPA that it might accept an outcome that allows Iran to retain a limited and extensively monitored uranium enrichment program.