Cannabis has been used for thousands of years, for a variety of medical, religious and recreational purposes. Today it is used by 178 million people each year, or 3.8% of the global population. Despite its long history and abundance, it is difficult to think of many psychoactive substances that polarise opinion more than cannabis. Preparations of the plant Cannabis Sativa L. and the 100+ chemicals it produces (called ‘cannabinoids’, such as delta-9-tetrahydrocannabinol or ‘THC’) show potential in a wide range of applications in modern medicine. These include multiple sclerosis, chronic neuropathic pain, intractable nausea and vomiting, loss of appetite and weight in the context of cancer or AIDS, psychosis, epilepsy, addiction, and metabolic disorders. Furthermore, when considering non-medical use, cannabis is often considered a ‘soft drug’; it is the only substance to have ever been reclassified to less harmful category in the UK Misuse of Drugs Act (this came into effect in 2004 but was reversed 5 years later). Nevertheless, strong concerns have been raised about the negative consequences of cannabis use. For example, it has been linked to an increased risk of psychotic disorders such as schizophrenia. However, it is not clear whether cannabis actually increases this risk, or if it simply coincides with other factors that do, as explained elsewhere on the BAP website.