Short physical half-lives—molybdenum-99 has a half-life of roughly 66 hours—mean that any delay in production, transport, or customs clearance directly reduces the usable quantity reaching the end user. Unlike most chemical imports, there is no inventory buffer: product decays in transit. This forces importers to maintain multiple approved supplier relationships and expedited clearance procedures, and any reactor outage at a producing facility creates immediate shortages in US nuclear medicine departments.

FDA oversight applies when a radioactive compound is intended for use as a drug or drug precursor in humans—for example, radiopharmaceutical-grade isotope generators or labeled compounds used in PET imaging. In those cases, the importer must satisfy both NRC import license requirements for the radioactive material and FDA admissibility requirements for the drug or device component. Coordination between the two agencies' review timelines is a practical compliance challenge.