Long-acting synthetic opioids (primarily illicit fentanyl) have surpassed prescription opioids as the most common drug involved in overdose deaths in the US. A major challenge in treating these overdoses is a phenomenon known as renarcotization: when the effects of naloxone wear off, the overdose victim begins to experience symptoms of overdose because the opioids are still present in their system. I am developing a novel microsphere formulation of naloxone that addresses renarcotization.