My research explores how cannabis use contributes to the development of psychosis using a new, standardised measure of cannabis exposure: Standard THC Units. Similar to standard alcohol units, this metric enables consistent assessment of cannabis use across studies. I apply it to quantify the risk of developing psychotic-like experiences in the general population and first-episode psychosis in clinical samples. Combining large-scale data analysis with interviews of individuals with psychosis, my work examines the transition from early symptoms to clinical disorder. This research aims to guide clinicians, support evidence-based policy, and establish safer cannabis use guidelines worldwide.