Over the last 15 years, there has been a steady increase in the development of orphan medicinal products (omps). This raises an important question: What impact does the eu marketing authorisation of an omp have on related research? This article establishes that the key orphan incentive, namely the 10‑year market exclusivity provision laid down in Article 8 of the eu Regulation on omps (Regulation 141/2000), has a huge potential impact on related research. It is argued that this provision can make it too difficult for researchers/sponsors to attain marketing approval for closely related products. This article advances two proposals to address this problem. First, it argues for new principles for assessing similarity, so as to clarify and narrow the ambit of market exclusivity. Secondly, it argues for improved conditions for a demonstration of ‘clinical superiority’ for similar omps.