Recilisib (also known as EX-RAD or ON-01210) is a radioprotectant, which means that this compound can protect cells from harmful effects of ionizing radiation. Unlike other radioprotectors, recilisib is not a free-radical scavenger or responsible for cell cycle arrest. Recilisib was suggested to have a different radiation protection mechanism involving DNA repair pathways. This compound has been studied as prophylactic (use prior to radiation exposure) and therapeutic (after exposure to radiation) drug. In studies with healthy volunteers, recilisib was rapidly absorbed and well-tolerated, with only mild adverse events. Phase I clinical trials have been completed.