Keep off the grass? Cannabis, cognition and addiction

Key Points Cannabis contains more than 100 unique ingredients that are known as 'cannabinoids', and the proportions of these vary widely across different strains of the plant. High-Δ 9 -tetrahydrocannabinol (Δ 9 -THC) varieties with negligible levels of cannabidiol (CBD) now dominate many Western markets and are more harmful than lower-Δ 9 -THC, higher-CBD varieties. Like other recreational drugs, Δ 9 -THC increases release of dopamine and opioid peptides (in preclinical studies) and alters endocannabinoid processing in the mesocorticolimbic reward system. Long-term Δ 9 -THC exposure leads to a downregulation of brain cannabinoid receptor function that reverses following abstinence. People who try cannabis are ninefold more likely to become addicted to it than to develop psychosis. Cannabis addiction is an increasing problem globally, and no effective pharmacological treatments currently exist — this remains a major unmet clinical need. The association between cannabis use and psychosis can be influenced by several vulnerability factors, including genetics, environmental factors and the frequency and type of cannabis used. Evidence linking cannabis use with the development of depression and anxiety is less consistent, although these disorders are often comorbid with cannabis addiction. The acute effects of cannabis on cognitive function are well documented, and the most robust, dose-related decrements are to working and episodic memory. Its long-term cognitive effects remain controversial, are influenced by many confounds and appear to subside a month after stopping use of the drug. We should ensure that global legislative changes are informed by neuroscience and public health. They should mitigate against adolescent uptake and the availability of highly potent products, including synthetic agents such as 'spice', that act as full cannabinoid receptor agonists. Cannabis is used widely as a recreational drug, and its legalization is an ongoing issue in several countries. Curran et al . review the cognitive effects of acute and chronic cannabis use, before discussing cannabis addiction and the psychiatric problems often comorbid with it. In an increasing number of states and countries, cannabis now stands poised to join alcohol and tobacco as a legal drug. Quantifying the relative adverse and beneficial effects of cannabis and its constituent cannabinoids should therefore be prioritized. Whereas newspaper headlines have focused on links between cannabis and