Whether or not using cannabis can lead to cognitive impairment is a hot topic of research and public interest. Given the extensive media attention to findings that suggest detrimental effects of cannabis on cognition, brain function and mental health, you would be forgiven for thinking smoking a spliff was akin to repeatedly bashing yourself over the head with a giant bong. However, since much of the work to date is cross-sectional (that is, measurements are taken only at one time in a person’s life), we cannot know whether cannabis users would have performed any differently before they started using cannabis.