Knowledge production and scientific research have become increasingly more collaborative and international, particularly in pharmaceuticals. We analyze international research networks on the country level in different disease groups. Our empirical analysis is based on a unique dataset of scientific publications related to pharmaceutical research. Using social network analysis, we find that both the number of countries and their connectivity increase in almost all disease groups. The cores of the networks consist of high income OECD countries and remain rather stable over time. We use network regression techniques in order to analyze the dynamics of the networks. Our results indicate that an accumulative advantage based on preferential attachment and point connectivity as a proxy for multi-connectivity are positively related to changes in the countries’ collaboration intensity.