Marijuana will become an unavoidable policy issue for health watchdogs in coming years, a conference heard Wednesday.
Growing scientific evidence about the medical benefits and a rollback of laws banning the drug mean that health agencies will have to make a determination on marijuana's use, experts said.
"The WHO (World Health Organization) will probably have to come up with a new stance on cannabis soon, given the pressure it is facing," Pavel Pachta, former deputy secretary of the International Narcotics Control Board, told the four-day Medical Cannabis and Cannabinoids conference, which opened in Prague on Wednesday.
The UN General Assembly is also due to hold a special session on drugs in 2016, bringing forward the date for the forum from 2019.
"In many countries across the world governments, policy makers, scientists, citizens... are actually questioning whether the current way of managing drugs is appropriate," Michel Kazatchkine, the UN's special envoy for AIDS in Eastern Europe and Central Asia, told delegates.
"The current international control system for drugs has failed," he said.
Kazatchkine urged prohibition to be replaced with "legal regulation" by governments that would reduce illegal markets and risks for people.
In Europe, the Czech Republic, Finland, the Netherlands, Portugal and Spain have legalised medical marijuana.
In the United States, 23 states have legalised marijuana for medical use while four plus the US capital have passed laws legalising it altogether.
Uruguay in 2013 became the world's first country to fully legalise marijuana.
"The exciting thing is we have over two million people using cannabis legally," said Steph Sherer, founder and head of the Americans for Safe Access organisation and herself a medical marijuana patient.
While opponents cite studies pointing to marijuana as causing lung cancer or psychosis, advocates contend the plant has a range of medical applications including pain and seizure management.
"In many cases we find that the endo-cannabinoid system works on some very basic mechanisms of the body, not just the symptoms of the disease but possibly on the mechanisms, on the basis of the disease," said Raphael Mechoulam, a Hebrew University professor and medical marijuana pioneer.
The endo-cannabinoid system refers to receptors in the human brain involved in body functions including appetite, pain, memory and mood.
These receptors are stimulated by the cannabinoid molecules in marijuana.
"So possibly in the next decade we shall have many drugs based on the endo-cannabinoid system," Mechoulam added.
Most major pharmaceutical producers have shied away from advertising cannabis-related products because of reputation issues and thin profits from non-patented substances, which includes marijuana's active components, he said.
"Now things I believe are changing and I understand a few of the major companies are developing drugs but none of them has reached the stage of being introduced as a medicinal agent," Mechoulam said.