Despite much speculation and conjecture over potential crossovers between terrorists and the drug trade in Europe, no study has examined the issue. This paper fills this gap by empirically examining such crossovers in the European Union between 2012 and 2017. Based on a unique open- source database, two main themes emerge. Firstly, the only area with deep and sustained crossovers is Northern Ireland, where Republican and Loyalist paramilitaries have sought to influence or control the drug trade. The consequences are threefold: conflict with “regular” criminals; internal divisions within paramilitaries; and the potential alienation of the very communities they claim to represent. Secondly, many European jihadists have backgrounds in consuming or dealing drugs, and their radicalisation does not always change this behaviour. Indeed, of the 69 jihadists who carried out an attack in Europe between 2012 and 2017, there is evidence that at least 5 individuals (7% of the total) consumed illicit drugs in the days or hours prior to their attack. This suggests that extremists do not automatically break from familiar, habitual, and possibly addictive patterns, and that radicalisation is no guarantee of an absolute, abrupt, and permanent change in lifestyle.