SYDNEY — A study published Friday in a British medical journal may have uncovered the secret behind Australia's laid-back lifestyle, and it turns out to be more than just sun and surf: The folks Down Under 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, found that Australia and neighboring New Zealand topped the lists globally for consumption of marijuana and amphetamines, a category of drugs whose use the study found to be growing rapidly around the world.

The study's co-authors, Louisa Degenhardt of the University of New South Wales and Wayne Hall of the University of Queensland, reported that up to 15 percent of the populations of Australia and New Zealand between 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.

The results reflected trends that have been in place for more than a decade, Hall said in an interview on Australian radio Friday. Despite the figures in the report, he said, the rate of marijuana use in Australia has been dropping "steadily for the better part of a decade."

The study found that marijuana was the world's most widely consumed illicit drug, with from 125 million to 203 million people partaking annually. Use of the drug far outstrips that of other illicit drugs globally, with 14 million to 56 million people using amphetamines, 14 million to 21 million using cocaine and 12 million to 21 million using opiates such as heroin, according to the study.

Despite marijuana's significantly outpacing other illicit drugs in terms of the volume of use, the study found that it was the least likely of all illicit drugs to cause death. Additionally, barely 1 percent of deaths in Australia annually can be attributed to illegal drugs, the report said, compared with almost 12 percent from tobacco use.

The prevalence of marijuana use in Australia is widely accepted if not openly condoned, and at least three states have moved to decriminalize the possession of small quantities for personal use.