Background: Many people use opioids and are at risk of overdose. Naloxone is an opioid antagonist used to counter the effects of opioid overdose. There is an increased availability of naloxone in New York City; however, many who use opioids decline no-cost naloxone even when offered. Others may have the medication but opt not to carry it and report that they would be reluctant to administer it if they were to witness an overdose. Objective: We aim to better understand why people who use opioids may be reluctant to accept, carry, and administer naloxone, and to inform the development of messaging content that addresses barriers to its acceptance and use. Methods: We conducted formative qualitative interviews with 20 people who use opioids who are 18 years and older in New York City. Participants were recruited via key informants and chain referral. Results: Participants cited 4 main barriers that may impede rates of naloxone acceptance, possession, and use: (1) stigma related to substance use, (2) indifference toward overdose, (3) fear of negative consequences of carrying naloxone, and (4) fear of misrecognizing the need for naloxone. Participants also offered suggestions about messaging content to tackle the identified barriers, including messages designed to normalize naloxone possession and use, encourage shared responsibility for community health, and elicit empathy for people who use drugs. Taken together, participants' narratives hold implications for the following potential messaging content: (1) naloxone is short-acting, and withdrawal sickness does not have to be long-lasting; (2) it is critical to accurately identify an opioid-involved overdose; (3) anyone can overdose; (4) naloxone cannot do harm; and (5) the prompt administration of the medication can help ensure that someone can enjoy another day. Finally, participants suggested that messaging should also debunk myths and stereotypes about people who use drugs more generally; people who use opioids who reverse overdoses should be framed as lay public health advocates and not just "others" to be managed with stigmatizing practices and language. Conclusions: It must be made a public health priority to get naloxone to people who use opioids who are best positioned to reverse an overdose, and to increase the likelihood that they will carry naloxone and use it when needed. Developing, tailoring, and deploying messages to address stigma, indifference toward overdose, fear and trepidation about reversing an overdose, and fear of police involvement may help alleviate fears among some people who are reluctant to obtain naloxone and use the medication on someone in an overdose situation.