Project Summary The opioid epidemic has continued to take a high death toll within the US, even accelerating during the pandemic. Stemming and stopping the pandemic will require a multi-prong effort along many health, social, even cultural dimensions. One important goal is to improve our ability to monitor the epidemic–both the speed of detection of opioid-use hotspots and precise geo- localization. Social media data represents an intriguing opportunity as it provides direct-report posts from the population–which may be useful for detecting and localizing opioid activity. However there has not been a careful systematic assessment of the utility (and pitfalls) for broad use of social media. In this proposal, we outline a plan to combine Reddit and Twitter to assess the ability to track opioid-associated mortality. We will focus on extracting mentions of fentanyl in social media, as it is responsible for the majority of deaths. We will also focus on modifiers that may be predictive of deadly use, particularly the use of opioids alone or in groups, the functional availability of naloxone, and the use of comorbid drugs. We will explore the limits of utility of social media data by aggregating it at multiple geo-spatial scales: national, regional, state and county (or county-sets that aggregate sparsely populated counties). We will also explore the time scales at which we can see relevant signals: annual, semi-annual, quarterly and monthly. Thus, we have two aims: 1. To assess the ability of social media together to provide signals of opioid use (through mentions of fentanyl and related synthetic opioids) that are correlated with mortality or proxies of mortality at multiple geo-spatial and temporal resolutions. 2. To assess the utility of social media to provide information about group vs. solo use, functional availability of naloxone and polypharmacy to modify the strength or urgency of opioid- use signals. The goal of our work is to generate a comprehensive preliminary assessment of the utility of social media, as it exists in the real world and at multiple scales, as a component of the opioid use surveillance system. Direct reports from the population may provide a useful “early warning” system that when combined with other sources, will provide policy makers and public health officials with a powerful set of tools for monitoring this public health crisis.