The experience with sanctions on Iran suggests some of the difficulties. In that case, the internal group likely to benefit most from sanctions is the Pasdaran, or Revolutionary Guards, which, coincidentally, may also prove to be the group most in favor of developing a nuclear weapons capacity. At the same time, sanctions strongly enhance the desire--or even the need--to insulate the economy from unreliable foreigners. In the process, this undercuts the influence of those who want to internationalize--the very group that is most likely to oppose nuclear weapons development.
In some cases sanctions may have a more exquisite counterproductive consequence. By effectively isolating the sanctioned country, as Hymans notes, scientists [Mueller means the sanctions isolate, not the scientists isolate] are less able to connect to peers in the international community. By contrast, in an open situation, scientists often join research institutes abroad and become less able, and perhaps less willing, to work on secret parochial projects at home. This sort of actual or effective brain drain can hamper a country's ability to fabricate a nuclear arsenal and, as physicist Richard Muller puts it, "a nuclear weapon designed by anything less than a top-level team is likely to fizzle."
The sanctions on Iran have also had another negative effect. Those desperately imploring Iran to eschew nuclear weaponry have, as a sweetener, sometimes offered to supply the Iranians with the nuclear fuel they need for their nuclear energy program. But because of the sanctions and the threat environment they are embedded in, the Iranians have been notably wary of such a deal because it would require them to be dependent on foreign suppliers who have proven themselves to be strongly hostile and could cut off the vital material at whim at any time, no matter what guarantees initially accompany the deal. To avoid the possibility of an externally induced energy crisis within the country, they have insisted on creating the fissile material required for the reactors themselves, a process that, however, would also allow them to produce a bomb more readily should they decide to do so at some point.