The goal of this clinical trial is to see if an injectable medicine called naltrexone can prevent fentanyl overdose deaths in people who use other drugs (cocaine, methamphetamine). The main questions it aims to answer are: What are the challenges for implementing naltrexone as an overdose prevention strategy? Are injections of naltrexone effective for opioid overdose prevention among people who use stimulants? How often are people who use stimulants and do not intentionally use opioids unintentionally exposed to opioids? Researchers will compare participants to receive the study medication to the usual care group to see if one group experiences fewer opioid overdose events than the other. Participants will be randomized to either receive a monthly injection of naltrexone over six months, or receive usual care. Usual care includes harm reduction supplies. Laboratory procedures will include the collection of urine, blood, and hair samples for various safety and outcome measure testing.