Recreational Drug Use at a Music Festival: A Dual Approach Using Hair Biomarkers Analysis and Participant Self-Reported Drug Use.

The growing prevalence of substance use and its associated health consequences highlights the need for reliable approaches to assess consumption patterns and validate self-reported data. This study, conducted at an international music festival in Portugal, aimed to characterise substance use by integrating objective toxicological findings with self-reported information. Quantitative hair analysis was combined with survey data from 249 participants recruited in 2022 and 2023. Hair samples were analysed by liquid chromatography-tandem mass spectrometry to detect psychoactive substances and metabolites. Self-reported use was assessed across multiple timeframes, from same-day consumption to use within the previous year. Alcohol (96%) and cannabinoids (90%) were the most frequently self-reported substances overall, based on lifetime self-reported use. Overall, 50% of participants tested positive for at least one compound in the analysed hair samples, with cocaine, MDMA and ketamine being the most commonly detected substances (24.5%, 24.1% and 22.9%, respectively). Some participants who denied consumption tested positive, particularly for MDMA and ketamine. Self-reported non-use was inversely associated with hair positivity for MDMA (OR = 0.25, 95% CI: 0.09-0.65) and ketamine (OR = 0.19, 95% CI: 0.09-0.40), compared with self-reported users. Discrepancies were also observed for cannabinoids, highlighting limitations of self-reported data. Strong correlations were identified between cocaine and benzoylecgonine, and between cannabis-related analytes (cannabidiol and THC), supporting the consistency of the toxicological results. Integrating self-reported data with objective biological measures improved data reliability, revealed polydrug use patterns and supported substance use monitoring in high-risk populations such as music festival attendees in this high-exposure festival setting.