The term 'problem drug user' (PDU) has risen to prominence in policy and research discourse over the past 25 years or so, particularly in the UK and Europe, largely at the expense of the older 'addiction' and 'dependence' concepts. How should we understand this shift? Is it merely a change in terminological fashion or does it signify something more significant? In exploring this question, the work of the philosopher Ian Hacking is drawn on, in particular his related ideas of 'making up people' and 'looping effects'. Although it first emerged in the early 1980s, it is shown how the idea of the 'PDU' in fact has a long and mixed genealogy which can be traced back at least as far as the 1930s, a heritage which continues to exert influence today. Following Hacking, it is argued that the invention just over 25 years ago of the 'PDU' constituted the creation of a new kind of person which did not exist before and which has shaped how those so labelled are governed and controlled. © 2011 Informa UK Ltd All rights reserved.