Ilumira, lutetium (177Lu) chloride, is a radiopharmaceutical precursor in the form of a solution containing the radioactive form of lutetium (177Lu), which is used to radiolabel other drugs.[1][6] The active substance mainly emits beta minus radiation for treatment and a small amount of gamma radiation for imaging, which delivers the drug to target cells in the body.[1][5] The European Medicines Agency (EMA) has decided that the benefits of this drug labeling precursor outweigh the risks, including radiation exposure, and it can be authorized in the EU, provided there is a medical benefit.[1][6] The most common side effects, affecting more than 1 in 10 people, include anemia, thrombocytopenia, leukopenia, lymphopenia, nausea, vomiting, and hair loss.[1] Lutetium (177Lu) has a half-life of 6.647 to 6.7 days and is produced by neutron irradiation of enriched lutetium or ytterbium.[3][4] The specific activity ranges from 500 GBq/mg to 3000 GBq/mg and the radioactivity in vials from 5.2 to 414.4 GBq at the reference time.[3][4] Recommendations for safe use, including radiation protection, are provided in the Summary of Product Characteristics and the Patient Information Leaflet.[1][5] Usage data is continuously monitored and suspected side effects are evaluated.[1]