The study, conducted with researchers from the University of Washington, compared drug policies and their enforcement at schools in Washington state and Victoria, Australia, to determine how they impacted student marijuana use.
The researchers found that while enforcement of anti-drug policies is a key factor in whether teens use marijuana, the way schools respond to policy violators matters greatly.
Students attending schools with suspension policies for illicit drug use were found to be 1.6 times more likely than their peers at schools without such policies to use marijuana in the next year — and that was the case with the student body as a whole, not just those who were suspended.
"That was surprising to us," said lead author Dr Tracy Evans-Whipp from the Murdoch Children's Research Institute. "It means that suspensions are certainly not having a deterrent effect. It's just the opposite."
In contrast, counselling and abstinence-based drug policies were associated with schools showing lower likelihood of marijuana use.
“Students in schools with a policy of sending policy violators to a teacher for counselling on the dangers of marijuana were almost 50 percent less likely to use marijuana,” said Dr Evans-Whipp.
The data, published in the American Journal of Public Health, came from the International Youth Development Study, a long-term initiative started in 2002 to examine behaviours among young people in Washington and Victoria. The two states were chosen as they are similar in size and demographics, but differ considerably in their approaches to drug use among students. Washington schools are more likely to suspend students, call police or require offenders to attend education or cessation programs, while Victoria schools emphasize a harm-reduction approach that favours counselling.
Researchers analysed results from over 3,000 students from Years 7 and 9 and nearly 200 school administrators in Washington state and Victoria across 2002 and 2003. Students were asked about their use of marijuana, alcohol and cigarettes and also about their schools' drug policies and enforcement. In both survey years, pot use was higher among Washington students than those in Victoria — almost 12 percent of Washington Year 9 students had used marijuana in the past month, compared with just over 9 percent of Year 9 students in Victoria.
After Washington legalised recreational marijuana use for adults in 2012, researchers decided to take a closer look at the data to determine how legalisation might influence students in Washington versus their counterparts in Australia, where marijuana remains illegal.
Dr Evans-Whipp said although the data studied predates marijuana legalization in Washington, the findings provide useful insights about what types of school policies are most effective in steering teens away from the drug.
“Since marijuana is the most commonly used illegal drug it is important for schools and state and federal agencies to identify effective methods for preventing its use. Our findings suggest that schools may reduce student marijuana use by delivering abstinence messages, enforcing nonuse policies, and adopting a remedial approach for policy violations rather than use of suspensions” the researchers conclude.