Nearly 4 percent of adults worldwide use marijuana, say Australian researchers who analyzed data from the United Nations' office on drugs and crime.
In 2006, 166 million people ages 15 to 64 used cannabis. Use was highest among young people in the United States, Australia, New Zealand and Europe, but the drug is becoming increasingly popular in low- and middle-income nations, Agence France-Presse reported.
About 9 percent of people who ever use marijuana become dependent on it, said the study. The risk of addiction for nicotine is 32 percent, 23 percent for heroin, 17 percent for cocaine and 15 percent for alcohol, they noted.
The researchers listed suspected negative health effects associated with regular cannabis use, including breathing and cardiovascular harm, psychotic episodes, poor school grades and car accidents, AFP reported.
The study appears in The Lancet.