Cannabis is the world's most popular illicit drug - and Australia and New Zealand top the list of users, an Australian study has found.
The research, published in the medical journal The Lancet, found that each year worldwide, about 200 million people use illegal drugs.
Cannabis is the most favoured drug of choice, and Australia and New Zealand were found to share the highest rate of usage.
An estimated 10 to 15 per cent of people aged between 15 and 64 smoked the drug in those two countries in the past year, the report says.
This compared with rates of 1.2 to 2.5 per cent in Asia, the region with the lowest usage.
Australia and New Zealand also share the highest rate of usage of drugs such as speed and crystal meth, with 2.8 per cent of their populations having ingested, injected or inhaled them over a 12-month period.
Report co-author Wayne Hall, of the University of Queensland's Centre for Clinical Research, said while marijuana could lead to dependence and mental disorders, other illicit drugs presented much higher risks.
"Cannabis was far and away the most widely used illicit drug globally, but heroin and other opiates cause the most harm, followed by amphetamine-type stimulants and cocaine,'' Professor Hall said.
"Among the most common harms were drug dependence, overdose deaths, accidents, violence, HIV-AIDS and other blood-borne infections.''
Worldwide, between 121 and 191 million people were estimated to be cannabis users in 2008.
Between 16 and 38 million people were problem users of opioids, amphetamines or cocaine and between 11 and 21 million people injected drugs.
About one in four users of opioids such as heroin become dependent on the drug for life.
The key risk factors for drug abuse are being male, sensation-seeking behaviour, poor school performance, and early oppositional and defiant behaviour, the study found.
It also reported that the number of deaths in Australia attributed to illicit drugs is far less than those caused by tobacco.
About 1.3 per cent of deaths in Australia are attributed to illicit drugs, compared with 11.7 per cent linked to tobacco use.
Alcohol abuse is responsible for 0.8 per cent of deaths, it said.
The report warned that many initiatives to control drug use are based on insufficient evidence.
It also said that beyond a certain point, increasing punishment for drug offences has diminishing benefits and can lead to negative side effects.
The report's authors suggest that nations wanting to try new approaches to drug legislation will have to move outside the existing international treaties.
They believe the existing international drug control system has not worked.
"The system's emphasis on criminalisation of drug use has contributed to the spread of HIV, increased imprisonment for minor offences, and contributed to legitimising extremely punitive national policies,'' their report said.
On the positive side, the rapid processing of drug offenders by special courts was showing some promise.
The report also said needle exchange programs were benefiting the broader community by reducing the transmission of infectious diseases.
The report said Australia had one of the lowest rates in the world of people infected with HIV, at just 1.5 per cent.
Only the Pacific Islands had a lower proportion, at 1.4 per cent.
The region with the highest rate of HIV infection is Latin America, at 28.8 per cent.