Drug checking services are being implemented in recreational settings across the world, however these projects are frequently accused of a lack of evidence concerning their impact on people who use drugs. This paper describes the implementation of a drug checking service at the Boom Festival 2016 and explores the impact of this service on its users' behavioural intentions.753 drug samples were submitted to the drug checking service for chemical analysis. All drug checking users were invited to fill a pre-analysis and a post-analysis questionnaire. 310 pre- and post-analysis questionnaires answered by users of the service were successfully matched.When the test results were "unexpected" (N = 86), 94.3% of the service users reported that they would not to take the drug. When the test result indicated the sample contained "the expected substance plus adulterants" (N = 41) 32% of users stated they would not take it. When the test result was "only the expected substance" (N = 370), as anticipated, 98% of the participants reported they would take it. There was a statistically significant association between users' behavioural intentions and drug-checking result (χ(2) = 350,042, p < .001).These results support the hypothesis that providing drug checking services in large-scale festivals helps users to better manage their drug use and deal with drug adulteration. The data corroborates the supposition that when provided with objective information about the content of their drugs, some users consider health protecting behaviours. Additionally, these results can contribute to the design of tailored harm reduction interventions that take into consideration clients' characteristics, profiles and motivations.