The aim of this study was to explore the reasons behind medicine shortages from the perspective of pharmaceutical companies and pharmaceutical wholesalers in Finland. The study took the form of semi-structured interviews. Forty-one pharmaceutical companies and pharmaceutical wholesalers were invited to participate in the study. The pharmaceutical companies were the member organizations of Pharma Industry Finland (PIF) (N = 30) and the Finnish Generic Pharmaceutical Association (FGPA) (N = 7). One company which is a central player in the pharmaceutical market in Finland but does not belong to PIF or FGPA was also invited. The pharmaceutical wholesalers were those with a nationwide distribution network (N = 3). A total of 30 interviews were conducted between March and June 2016. The data were subjected to qualitative thematic analysis. The most common reasons behind medicine shortages in Finland were the small size of the pharmaceutical market (29/30), sudden or fluctuating demand (28/30), small stock sizes (25/30), long delivery time (23/30) and a long or complex production chain (23/30). The reasons for the medicine shortages were supply-related more often than demand-related. However, the reasons were often complex and there was more than one reason behind a shortage. Supply-related reasons behind shortages commonly interfaced with the country-specific characteristics of Finland, whereas demand-related reasons were commonly associated with the predictability and attractiveness of the market. Some reasons, such as raw material shortages, were considered global and thus had similar effects on other countries.