One arm of the largest cognitive testing initiative in the world, the Great British Intelligence Test, surveyed participants about their use of recreational drugs such as psychedelics. The study run longitudinally between December 2019 and January 2023, and assessed participant at 6-monthly timepoints. During the initial 6 month recruitment period 500k individuals signed up, and 95k agreed to be recontacted for longitudinal assessments. At every recontact timepoint between 15k and 35k individuals responded, out of which 1 in 3 were recreational drug users and 1 in 10 were psychedelics users. Importantly, questions about recreational drug use were only asked at recontact, not at recruitment, and were not disclosed prior to participation, therefore mitigating selection bias characteristic of studies recruiting substance users online. We used the data accumulated in this way to answer a number of questions: 1) how do psychedelic users differ in terms of their cognitive abilities and mental health status relative to individuals who use other drugs or never used drugs before, 2) what were their cognitive and mental health trajectories and how did these evolve as a function of changes in levels of drug use, 3) were users of psychedelics more psychologically resilient during the COVID-19 pandemic, 4) is there any relationship between the use of psychedelics, trust in bodies of authority and compliance with their guidelines? This talk will summarise the findings and discuss their relevance in the wider discourse around the use of psychedelics.