Assessing cannabis use among portuguese university students: a multidimensional study using survey data and hair and oral fluid analysis.

According to the most recent report from the European Union Drugs Agency (EUDA), 18.6% of young adults in Europe used cannabis in 2024. In Portugal, cannabis use among young adults remains poorly characterized, with the latest national survey from 2025 reporting a 21% prevalence. Survey-based data are susceptible to bias, underscoring the need for complementary biological monitoring. This study assessed cannabis use among Portuguese university students using hair and oral fluid (OF) testing, which are non-invasive and provide complementary insights: OF reflects recent consumption, while hair reflects mid- to long-term use. Hair and OF samples from 938 participants across nine universities in northern, central, and southern Portugal were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for THC, THC-OH, THC-COOH, CBN, and CBD. Participants completed questionnaires on cannabis use, demographics, and consumption behaviors. Associations between self-reported use and measured concentrations were examined, and factors influencing cannabinoid levels were analyzed statistically. Cannabinoid detection rates varied across universities, with northern institutions showing the highest concentrations. OF reflected recent use, whereas hair captured longer-term exposure. Concentrations were influenced by geographic region, tobacco use, and social context of consumption, whereas demographics, age at first use, opinions on legalization, and most hair treatments had minimal impact. Discrepancies emerged between self-report and analytical findings. These findings demonstrate that combining self-report with biological monitoring provides a more accurate and comprehensive assessment of drug use. Regional heterogeneity underscores the value of multi-matrix approaches for research, public health surveillance, and evidence-based interventions, and empathizes the need for updated national data.