The International Cannabis Consortium (ICC) is a multicohort project that has been running for over a decade. The aim is to identify genetic variants that increase chances for different cannabis use behaviours. Following 3 large genome-wide association studies on lifetime cannabis use in 2016 (N~35,000) and 2018 (N~185,000) and on age at cannabis initiation in 2018 (N~29,000). The consortium is now working on analyses on cannabis use frequency (N~ 269,000) and lifetime cannabis use in multiple ancestry groups (N~590,000). Twenty-four cohorts from countries all over the world have contributed data to the current project.

With large increases in sample size, more and more genetic variants are identified that play a role in cannabis use. These results are used to answer clinically important research questions. For instance, this project has identified shared vulnerability between cannabis use and a range of risk behaviours and mental health issues. The study contributes to uncovering biological pathways and finds associations with protein signaling in specific brain areas. Leveraging results from genetics, putatively causal effects of cannabis use can be investigated, such as its effect on schizophrenia.

This large-scale collaboration brings together data from all over the world. And it showcases the power of open science for discovery. Providing insight into causes of risk behaviour and targets for prevention and intervention.