Background: Early identification of new drug trends and rapid intervention is high up on the political agenda. It has been argued that traditional drug monitoring systems are tired and need revamping, with methods lacking roots in the latest theoretical advances. In particular, current systems fail to utilise and apply theory in research practice. Aim: This presentation explores the way in which theoretical models can be utilised to facilitate the construction of more effective systems for monitoring emerging drug trends. Theory can assist with questions such as: Why do trends start? In what conditions or circumstances are trends likely to develop? Where are they likely to emerge – both geographically and demographically? How do trends ‘behave’, in particular what mechanisms lead to their spreading? Methods: Drug trend behaviour is explored using a ‘pragmatic’ research paradigm with reference to a variety of epidemiological, social, cultural and economic theories. The usefulness of diffusion theory, cultural theory, open marginality and complexity are explored. Two steps are presented. The first is selection of key theoretical approaches which provide useful understanding and shed light on the problem of drug trend behaviour. The second is consideration of the practical implications of these approaches - how theory can be used to improve our drug trend monitoring models and practice. Results & Discussion: Reflection on theory provides some indications for the development of more effective monitoring systems. In particular it guides us in terms of the sources should we use, the populations should we follow, and the reporting timescale that is required.