A regular cannabis user currently has no way to know whether their consumption is low-risk or dangerously high, unlike drinkers who can count alcohol units. This research will create the first practical tools for measuring cannabis intake—similar to a drinks diary—and propose evidence-based guidelines for safer use. The problem is stark: over 200 million people use cannabis globally, yet no official guidance exists on what constitutes low-risk consumption. In the UK, where possession is a criminal offence carrying up to five years in prison, policymakers lack basic data on how much cannabis people actually use or what it contains. This project will fill that gap by conducting regular national surveys and chemical tests of cannabis samples. If successful, the research could transform how doctors advise patients, how individuals self-monitor, and how governments design drug policy. By comparing long-term data from the UK and Canada—where cannabis is legal—the team will model how different policies affect use and harm. This could give policymakers concrete evidence to decide whether prohibition, decriminalisation, or legalisation best reduces harm, rather than relying on ideology.
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Cannabis is a widely used drug globally, with over 200 million consumers. Despite its widespread use, there is lack of guidance to help people use cannabis more safely. For example, people who use alcohol can reduce their risks by adhering to safer use limits e.g., "do not regularly exceed 14 units per week". This research will develop new resources to help people record how much cannabis they are using (like calculating alcohol unit consumption) and recommendations for safer levels of use. These resources could help people to self-monitor their own cannabis use and make informed choices to reduce harm. They could also be used by people who give advice to people about their cannabis use in professional settings (e.g., doctors). Our understanding of how much cannabis is used and what cannabis contains is extremely limited in the UK. This research will also conduct regular surveys of the UK population and tests of cannabis samples. This will improve our understanding of the extent of cannabis use and its effects in the UK, and how this compares to other countries. This information could help policy makers to decide how to best to manage cannabis use. For example, cannabis use is prohibited as a criminal offence in the UK. This means that personal use of cannabis can lead to a prison sentence of up to five years, an unlimited fine, or both. Other countries have introduced different approaches. For example, people are legally permitted to purchase and use cannabis for recreational purposes in Canada. However, it is unclear which type of policy is best for reducing cannabis harms. Therefore, this research will make use of long-term data collected in the UK and other countries such as Canada. It will use this information to make predictions about how cannabis use and cannabis harms might change under current policy (e.g., prohibition) and alternative policies (e.g., legalisation). This will help policy makers in the UK and other countries to make decisions about how to best to reduce the harms of cannabis use.
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