Using cannabis as a teenager may negatively affect educational attainment, new findings suggest. About seven percent of U.S. high school seniors are daily or near-daily cannabis users, and surveys indicate that use is increasing.
Dr. Edmund Silins of the University of New South Wales, Australia, and colleagues explain that, “Persisting questions about the long-term effects of adolescent cannabis use have clouded debate. The existing evidence has limitations, and so the picture of adolescent cannabis use and its putative health consequences is fractured.”
In order to address the risk of cannabis on “important domains of well-being during the transition to adulthood,” the team recently carried out a study of 3,765 cannabis-using participants from three large, long-term studies based in Australia and New Zealand. Analysis took into account 53 related factors such as age, sex, ethnicity, socioeconomic status, use of other drugs, and mental illness.
This showed “clear and consistent associations” between frequency of cannabis use during adolescence and most of the outcomes investigated: completing high school, obtaining a university degree, cannabis dependence, use of other illicit drugs, suicide attempt, depression, and welfare dependence.
These risks increased with increasing dose, with those who used cannabis daily facing the highest risks.
Those who were daily users of cannabis before the age of 17 were more than 60 percent less likely to finish high school or obtain a degree than those who never used it. Daily cannabis users in adolescence were also seven times more likely to attempt suicide, had 18 times the risk of cannabis dependence, and were eight times as likely to progress to other illicit drugs.
The study findings are published in The Lancet Psychiatry.
Said Silins, “Our results provide strong evidence that the prevention or delay of cannabis use is likely to have broad health and social benefits. Efforts to reform cannabis legislation should be carefully assessed to ensure they reduce adolescent cannabis use and prevent potentially adverse effects on adolescent development.”
The authors believe there are several aspects of the study that support a causal relation: There are strong associations between cannabis use and all young adult outcomes; there is a dose-response association with increasing use; and most associations were not explained by potential “confounding” factors such as mental health problems.
However, Silins and colleagues point out studies such as these “are limited in their capacity to explain the mechanisms behind such associations.” Some research suggests a damaging effect on central nervous system development, but equally, cannabis use at a young age could reflect background factors “that place young people at increased risk of adverse psychosocial outcomes” but that are not adequately controlled for in studies to date.
The researchers feel confident that their findings are also relevant to young people in other high-income countries (e.g. the U.S., Canada, and the U.K.) but they make the point that “the social and legislative context of cannabis use varies between regions, and remains an important consideration in the generalization of these findings.”
Commenting on the study, Merete Nordentoft, M.D., Ph.D., of the University of Copenhagen, Denmark, writes, “Persistent cannabis use has adverse effects, such as low energy and initiative, and impairment of cognitive functions, and these factors are likely to mediate the harmful effect of cannabis on educational attainment. Findings from randomized clinical trials show a negative short-term effect of cannabis intake compared with placebo on cognitive function during, and in the hours following, intoxication.”
Nordentoft makes the point that a randomized clinical trial exposing some young people to cannabis over the long term, and comparing them with others given placebo “will never be done.” Therefore, findings can only come from naturalistic experiments such as this one.
“The convincing results presented by Silins and colleagues are very valuable and highly appropriate at a time when several American states and countries in Latin America and Europe have decriminalized or legalized cannabis and allow unrestricted marketing of various formulations of the drug.”
Nordentoft fears that these changes “will probably be followed by decreased prices and increased use, which will lead to more young people having difficulties with school completion and social and personal maturation, and will increase the risk of psychosis.”
“Youth is a very vulnerable period in life,” she said. “Socially, young people need to develop and mature, and to prepare themselves to meet demands in their adult life, such as completing education and finding employment, choosing leisure activities, and finding partners and friends. Cannabis use, especially frequent use, impairs this development and reduces the likelihood that a young person will be able to establish a satisfactory adult life.”
Silins, E. et al. Young adult sequelae of adolescent cannabis use: an integrative analysis. The Lancet Psychiatry, Volume 1, No. 4, p286-93, September 2014.