This paper explores drivers and barriers to cross-border economic integration in the Ireland-Northern Ireland context. Via a case-study of the Irish pharmaceutical sector, we show that potential economic benefits of an all-island sectoral ecosystem have been recognised by businesses and policymakers in both jurisdictions. However, those economic benefits within the pharmaceutical sector have not materialised. We explore this situation by employing the concept of proximity. Proximity refers not only to geographic or spatial proximity, but also encompasses cognitive, organizational, institutional, and social proximities. Our findings indicate that a mix of proximities are necessary in order to overcome impediments to cross-border economic integration. While industry actors may enjoy geographical proximity due to their business locations and cognitive proximity in terms of overlapping industry and scientific knowledge, without the requisite institutional and social proximities cross-border economic integration may struggle to achieve its potential.