SYDNEY — A study published Friday in a British medical journal may have finally uncovered the secret behind Australia’s laid-back lifestyle, and it turns out to be more than just sun and surf: The denizens Down Under, it turns out, consume more marijuana than any other people on the planet.

The study, an analysis of global trends in illegal drugs and their effect on public health published in The Lancet, a prestigious journal, found that Australia and neighboring New Zealand topped the lists globally for consumption of both marijuana and amphetamines, a category of drugs whose use the study found to be growing rapidly around the world.

The study’s co-authors, Professors Louisa Degenhardt of the University of New South Wales and Wayne Hall of the University of Queensland, reported that as much as 15 percent of the populations of Australia and New Zealand between the ages of 15 and 64 had used some form of marijuana in 2009, the latest year for which data were available.

The Americas, by comparison, clocked in at 7 percent, although North America batted above the neighborhood average with nearly 11 percent of its population partaking. Asia demonstrated the lowest global marijuana use patterns at no more than 2.5 percent, the study said, although difficulties in obtaining accurate data in less developed countries were cited as one possible reason for the low figures.