Objective: This study tested potential moderator interactions between components of the Theory of Planned Behaviour (TPB) in relation to ecstasy use, extending previous research. It was expected that attitudes, subjective norms and perceived behavioural control (PBC) would moderate each other in predicting intended use of this drug.Method: A cross‐sectional survey was administered to 200 young adults.Results: In hierarchical multiple regression analysis, past behaviour and attitude independently predicted intention; previous use of ecstasy and more positive attitudes towards ecstasy use were associated with stronger intentions to use this drug in the future. Moreover, there was a significant interaction between attitude and PBC (R2change= 0.05). Slope analysis revealed that PBC better predicted intention given more positive attitudes towards ecstasy use.Conclusions: This moderator function may help explain predictive inconsistencies reported in the literature. Implications for the TPB are considere