A global tracking project to measure the daily mental health impacts of cannabis use over two years has been launched, with the aim of mapping how local laws, individual mindsets and daily routines shape outcomes. The project, led by Nora de Bode of Erasmus University Rotterdam, seeks to understand why cannabis affects people so differently and to chart both potential benefits and harms as use grows worldwide. The study protocol was published in Comprehensive Psychiatry.
As cannabis laws relax around the world, usage is on the rise. While many people use the plant recreationally, an increasing number turn to it for medical reasons, often for pain management or relief from mental health symptoms. The effectiveness of cannabis for mental health remains fiercely debated, with some users reporting anxiety relief and mood stabilisation, while others experience adverse effects such as worsened depression, paranoia and, in some cases, cannabis use disorder.
Researchers say the variability in outcomes likely reflects a mix of factors, including the chemical makeup of cannabis products. THC, the compound that produces the psychoactive high, and CBD, which does not, play central roles. High THC doses are generally linked to greater risk of adverse mental health effects, but preexisting psychiatric conditions and biological vulnerabilities also influence individual reactions.
Historically, studies on cannabis have tended to focus narrowly on harms or benefits, and have been constrained by funding, disciplinary boundaries and variable contexts. The literature has often overlooked environmental and cultural factors—such as social stigma, local policing practices and community norms—that shape how people experience cannabis. Moreover, many medicinal users purchase and use cannabis outside formal medical supervision, complicating clinical tracking.
The team behind the project, titled “Blowing Minds,” is led by Nora de Bode, with Erasmus University Rotterdam colleagues Emese Kroon, Jia Hua Hsieh and Janna Cousijn contributing to the protocol.
The researchers plan to recruit about 1,800 participants aged 18 to 65 who use cannabis at least four times a week. The study will compare recreational with medicinal users and recruit from multiple regions to capture different legal environments. The initial rollout includes the Netherlands, the United States, Canada and Brazil, with plans to expand into parts of Asia and Africa.
The study will be conducted entirely online. Participants complete baseline questionnaires detailing their preferred methods of consumption, product potency, physical health, sleep quality and any history of trauma or mental illness. They also reflect on social pressures from friends, family and government that may influence their cannabis use.
Following the baseline assessments, participants undergo a series of digital cognitive tests measuring memory, processing speed, general intelligence and emotional perception. One test specifically gauges how readily cannabis-related images capture attention, an indicator the researchers deem relevant to potential addictive behaviours.
After baseline, participants embark on a 14-day intensive tracking period using a mobile app, employing the experience sampling method. Each morning they report sleep quality and any substance use from the previous day, and then receive five random prompts throughout the day to log mood, stress levels and cannabis cravings within an hour of each prompt. They also log mood just before they consume cannabis, recording their intention to use and immediate emotional state.
By comparing mood and craving data gathered prior to use with later log-ins, the researchers aim to identify emotional triggers for use and how the drug alters mood in the hours afterwards. The project is designed to extend well beyond the initial two weeks, with follow-ups at one and two years after baseline. Participants will retake cognitive tests and mental health questionnaires, enabling the team to chart long-term trajectories and assess whether certain coping strategies—such as using highly potent products to manage negative emotions—are associated with cognitive decline or worsening mental health over several years.
Logistical challenges accompany remote, multi-year research. Because participants are compensated, the online format is susceptible to fraudulent responses, including multiple entries or automated completion. The team applies digital security measures to flag suspicious activity, checks for contradictory demographic data and verifies regional locations using internet routing data.
Participant fatigue and dropout are expected in such a long study. The researchers will use statistical models capable of handling missing data to maintain the integrity of their analyses and conclusions.
By making their digital materials and anonymised data available to other scientists, the team hopes to standardise how cannabis habits are measured worldwide. The aim is for other laboratories to replicate the study in different countries or among specific age groups, using the shared framework as a blueprint.
The study, “Blowing minds: A cross-cultural, longitudinal investigation to unravel the highs and lows of recreational and medicinal cannabis users,” was authored by Nora de Bode, Emese Kroon, Jia Hua Hsieh, and Janna Cousijn.
