Edmund Silins, L John Horwood, George C Patton, David M Fergusson, Craig A Olsson, Delyse M Hutchinson, Elizabeth Spry, John W Toumbourou, Louisa Degenhardt, Wendy Swift, Carolyn Coffey, Robert J Tait, Primrose Letcher, Jan Copeland, Richard P Mattick, for the Cannabis Cohorts Research Consortium
Marked shifts have taken place in attitudes to cannabis use.1 Moves to decriminalise or legalise cannabis use in several US states and Latin American countries are a sign of such changes in public opinion. 2 These shifts have happened while debate continues about the long-term health and social sequelae of adolescent cannabis use. 3,4 Additionally, in some countries adolescents are initiating cannabis use earlier than have those in previous years5 and more adolescents are using cannabis heavily. 6–8 In England, 4% of 11–15 year olds are past-month cannabis users; 7 about 7% of US high-school seniors are daily or near-daily cannabis users; 8and in Australia, less than 1% of 14–19 year olds use daily and 4% use weekly.6 This prevalence is particularly concerning because adolescence seems to be a vulnerable developmental period for the consequences of cannabis exposure, 9 and evidence suggests that early use of cannabis is associated with increased risk of adverse developmental outcomes.