How to ask about the use of new psychoactive substances to increase the validity of results in self-report prevalence surveys.

Generic questions might lead to notably lower estimates of self-reported NPS use in comparison to checklists. However, creating relevant checklists is challenging and lengthy survey instruments have limitations. Further surveys might benefit from featuring a combination of the strategies used in this study-a single (generic) question involving a number of locally specific NPSs and a free-text 'other' probe.