CHICAGO - Kids on both sides of the Atlantic are smoking less pot and going out less often with friends at night, a study of 15-year-olds in 30 countries found.
The double declines occurred in the United States, Canada and most European countries from 2002 to 2006. The trends likely are related, because other research has found that kids who spend many evenings out are more likely to smoke marijuana than homebodies.
Because few parents approve of marijuana use, teens are most likely to use the drug secretly away from home, said lead author Emmanuel Kuntsche of the Swiss Institute for the Prevention of Alcohol and Drug Problems.
Reasons for the declines are unclear. But the researchers said drug-prevention efforts and technology may have contributed.
Instant messaging, e-mail and cell phones "may have partly replaced face-to-face contacts, leading to fewer social contacts in the evenings," Kuntsche said.
The study appears in February's Archives of Pediatrics and Adolescent Medicine, released Feb. 2.
The researchers analyzed data on 93,297 15-year-olds from periodic health surveys in dozens of countries conducted in collaboration with the World Health Organization.
Survey questionnaires were distributed to entire classrooms at various schools, asking various health-related questions including about marijuana use and evenings out with friends in the last year. Responses to 2006 surveys were compared with those in 2002.
Users were kids who'd tried marijuana at least once in the last year.
Marijuana use increased only in Estonia, Lithuania and Malta, and among Russian girls.
While rates varied widely among countries, prevalence was highest both years in Canada, where 30 percent of boys and almost 28 percent of girls used marijuana in 2006. That was down 13 percent among boys and almost 10 percent among girls.
The United States ranked third in 2006, with 24 percent of boys and girls each reporting marijuana use. That was down almost 12 percent among boys and 2 percent among girls, echoing previous reports of declining marijuana use among U.S. teens.
Switzerland ranked second in prevalence among boys, and Wales was second among girls. Greece, Macedonia and Sweden were at the bottom of the list - fewer than 5 percent of boys and girls reported use in 2006.
Average number of evenings out also decreased in most countries. In the United States, nights out fell slightly to about twice a week in 2006 for boys and girls.
An Archives editorial said that while evenings out may increase chances for marijuana use, parents shouldn't discourage socializing because teens need time away from home to gain independence. Instead, the editorial advises, parents should help steer kids to activities that don't encourage drug use.