Background/Aims: To assess whether novel psychoactive substances (NPS) displace established club drugs, supplement them or act as drugs of initiation via a study of the relationship between mephedrone, ecstasy pills, cocaine and MDMA powder amongst club-goers considered to be ‘early adopters' of psychostimulant/club drug trends. Methods: In situ surveys were conducted with 308 customers in two south London gay dance clubs across 3 weekend nights in July 2010 to assess the prevalence and patterns of self-reported use of a range of illegal drugs and NPS. Results: Mephedrone was added to existing drug repertoires amongst those surveyed and acted to supplement more established club drugs including ecstasy pills, cocaine and MDMA powder, rather than replacing or displacing those drugs. Conclusion: This survey suggests that NPS are likely to be added to drug repertoires, particularly amongst experienced users with consequent health risks for individuals and resource implications for services. This study points to a complex relationship between NPS and illegal drug availability, purity and regulatory control, one which is increasingly important to understand given the global emergence of NPS and the challenges they present to existing supply, demand and harm reduction strategies.