The Mental Health Risks of Adolescent Cannabis Use

S ince the early 1970s, when cannabis fi rst began to be widely used [1], the proportion of young people who have used cannabis has steeply increased and the age of fi rst use has declined [2,3]. Most cannabis users now start in the mid-to-late teens [1], an important period of psychosocial transition when misadventures can have large adverse effects on a young person's life chances. Dependence is an underappreciated risk of cannabis use [1]. There has been an increase in the numbers of adults requesting help to stop using cannabis in many developed countries, including Australia [4] and the Netherlands [1,5]. Regular cannabis users develop tolerance to many of the effects of delta-9-tetrahydrocannabinol [6–8], and those seeking help to stop often report withdrawal symptoms [9-11]. Withdrawal symptoms have been reported by 80% of male and 60% of female adolescents seeking treatment for cannabis dependence [12,13]. In epidemiological studies in the early 1980s [14] and 1990s [15], it was found that 4% of the United States population had met diagnostic criteria for cannabis abuse or dependence at some time in their lives. Surveys in Australia, Canada, and New Zealand have produced similar estimates [16– 19]. About one in ten of those who use cannabis meet criteria for dependence [15], but this risk is much higher for daily users and persons who start using at an early age [20,21]. Only a minority of cannabis-dependent people in surveys report seeking treatment (Chapter 7 of [1]), but among those who do, fewer than half succeed in remaining abstinent for as long as a year [9,10,22]. Those who use cannabis more often than weekly in adolescence are more likely to develop dependence, use other illicit drugs, and develop psychotic symptoms and psychosis [1]. Establishing whether cannabis use is a contributory cause of these outcomes [1] requires two things: (1) longitudinal research on the effects that cannabis use in adolescence has on psychosocial outcomes in young adulthood [23], and (2) statistical methods to control for the fact that young people who regularly use cannabis differ from their peers who do not in ways that increase regular cannabis users' risk of these adverse psychosocial outcomes [1,23]. The Essay section contains opinion pieces on topics of broad interest to a general medical audience. Citation: Hall W (2006) The mental health risks of adolescent cannabis use. PLoS Med 3(2): e39. article distributed under the terms of the Creative …