The thesis investigates the dynamics that surround participants' responses to questions about illicit drug activities. By examining the attributional and discursive literatures, the opening chapters (Chapters 1 and 2) outline the difficulties associated with assuming veridicality in question-answer dyads. Emphasis is placed on the essentially social and intentional foundations of the applied research procedure. The existing research on methodological effects in substance research is outlined at the start of Chapter 3. These form the foundation for the empirical investigations that constitute the remainder of the thesis. The studies carried out attempt to examine methodological issues in the context of applied research procedures that combine quantitative outcomes with qualitative considerations such as reflexive consideration of the role of the researcher and the status of the participant. The first investigation demonstrates the influence of treatment status on the discourse provided by adult substance users. Drug users in contact with treatment services provide drug-related explanations distinct from those given by users who are not in treatment. This distinction is assessed in terms of a theoretical model of addiction based on discursive criteria and contextual influence (Chapter 4). These contextual influences are further examined in the empirical studies presented in Chapters 4 and 5 in which the subjects are young people whose drug experiences are assessed in the context of drug education (Chapter 5) and treatment and service needs (Chapter 6). Each of these investigations attempts to demonstrate the sophistication of discourse that respondents exhibit in their drug-related conversations and the ways in which their attitudes and understandings of these topics are shaped by the context of the experiences they have had.