OBJECTIVE This paper describes the misrepresentation of LSD at Portugal's Boom Festival 2014 and the prevention of unintentional consumption of DOx and 25x-NBOMe among LSD consumers attending a drug-checking service. METHODS Two hundred forty-five drug samples expected to contain LSD were submitted to the drug-checking service for chemical analysis. One hundred ten post-test questionnaires were successfully matched with test results. RESULTS About 67.3% of the alleged LSD samples tested contained only LSD; 0.8% contained LSD combined with adulterants; 24.1% did not contain LSD but did contain another psychoactive substance, including 11.4% that were 2,5-dimethoxyamphetamine derivatives and 9.8% that were N-benzyl-2,5-dimethoxyphenethylamine derivatives; and no psychoactive substance was detected in 7.8%. The majority of service users who received unexpected test results regarding their alleged LSD (74.2%) reported that they did not intend to consume the drug. Following dissemination of alerts on day 2, a larger than expected proportion of all tests conducted were for LSD, when comparing the 2014 festival to 2012, where no such alert was disseminated. CONCLUSIONS Although these results support the provision of integrated drug-checking services in party settings, evidence of their utility and effectiveness would be improved through future research incorporating more robust measures of outcomes following provision of drug-checking results.