The geography of the U.S. opioid epidemic has shifted across successive waves. After a period in which overdose mortality increasingly burdened rural and suburban communities, the fentanyl era appears to have redirected harm toward dense urban cores. We document this post-2015 urbanization using national mortality microdata from CDC WONDER and inpatient discharge records from Pennsylvania. We show three patterns. First, urban overdose mortality rises sharply after fentanyl becomes the dominant illicit opioid. Second, within large metropolitan areas, overdose rates diverge between core counties and suburban peripheries, with especially large gaps in eastern metros, where fentanyl diffused earlier and more intensely. Third, within the Philadelphia region, overdose-related inpatient admissions become increasingly concentrated in a small number of central-city ZIP codes, especially near longstanding drug-market hotspots. We argue that this shift reflects both supply- and demand-side changes associated with fentanyl. If overdose risk is becoming more spatially concentrated, then naloxone distribution, outreach, enforcement, and emergency response may be more effective when targeted to a narrower set of urban locations.