Laws against cannabis have failed to cut its use around the world and have led to policies that are intrusive, socially divisive and expensive, according to an international group of drug policy experts.
In a book published on Tuesday looking at cannabis policies, the experts said that, while the drug harmed some users, it had only a modest effect on society, where cocaine and alcohol were potentially more damaging.
"It is time for governments around the world to readdress cannabis policy," Peter Reuter, a professor of public policy at the University of Maryland in the United States and one of the book's five co-authors, told Reuters in an interview.
Scientific research has suggested smoking cannabis can double the risk of developing psychosis. A study published in the British Medical Journal last month found people who smoked "skunk" — a potent form of cannabis — are almost seven times more likely to develop psychotic illnesses such as schizophrenia than those who smoke "hash", or cannabis resin.
Reuter said authorities should acknowledge "growing evidence that criminalization of use is a minor deterrent" and recognize the importance of developing "responsible ways of managing supply, rather than creating large illegal markets".
He said the increasing potency of cannabis being sold on the street in many Western countries was one of his major concerns. "What we really need is a safer was way in which people can buy the drug, rather than leaving it to an illegal market which is producing a drug that is strong and stronger," he said.
"It's an additional but increasingly important argument for why we have to face up to working out how to provide a regulated market for cannabis."
The book, called "Cannabis Policy: Moving Beyond Stalemate", was published by Britain's Oxford University Press and the Beckley Foundation, a charity that favors regulating rather the criminalizing drugs.
"Prohibitionist policies not only fail to meet their objectives but have inflicted significant social harms in the process," said Amanda Feilding of the Beckley Foundation.
Despite laws against its use, up to 190 million people around the world use cannabis, according to U.N. estimates, which equates to about 4 percent of the global adult population.
The authors said vast numbers of arrests for possession of cannabis in countries such as Britain, Switzerland and the United States had had little deterrent effect but caused social division and pointless government expense.