The so-called war on drugs is failing to curb supply despite the increasing amounts of funding being ploughed into law enforcement, medical researchers have warned.
Street prices of illegal drugs have fallen in real terms since 1990 while the purity of the substances has generally increased, a sign of increased availability, according to the research published in the online journal BMJ Open.
Most national drug control strategies have focused on law enforcement to curb supply despite calls to explore other approaches, such as decriminalisation and strict legal regulation, the report said.
It comes after Durham chief constable Mike Barton claimed decriminalisation was the best way to wrestle power away from criminal gangs.
Writing in The Observer, the national intelligence leader for the Association of Chief Police Officers also suggested the NHS should supply class-A drugs such as heroin and cocaine to addicts.
The BMJ Open study looked at data from seven international government-funded drug surveillance systems which had at least 10 years of information on the price and purity of cannabis, cocaine and opiates, including heroin.
The report said "the global supply of illicit drugs has likely not been reduced in the previous two decades" and added " the data presented in this study suggest that the supply of opiates and cannabis have increased, given the increasing potency and decreasing prices of these illegal commodities".
It concluded: "These findings suggest that expanding efforts at controlling the global illegal drug market through law enforcement are failing."
Co-author Dr Evan Wood, scientific chair of the International Centre for Science in Drug Policy, said: "T hese findings add to the growing body of evidence that the war on drugs has failed.
"We should look to implement policies that place community health and safety at the forefront of our efforts, and consider drug use a public health issue rather than a criminal justice issue.
"With the recognition that efforts to reduce drug supply are unlikely to be successful, there is a clear need to scale up addiction treatment and other strategies that can effectively reduce drug-related harm."
The United Nations recently estimated the illicit drug trade is worth at least 350 billion US dollars (£217 billion) every year.
The BMJ Open study also reviewed the number of seizures of illegal drugs in drug production regions and rates of consumption in markets where demand for illegal drugs is high.
Among the findings, the report said in Europe, the average price of opiates and cocaine, adjusted for inflation and purity, decreased by 74% and 51% respectively between 1990 and 2010.
Danny Kushlick, head of external affairs at think-tank Transform Drug Policy Foundation, said: "This research should serve as a wake-up call to policymakers to legally regulate drugs as an urgent priority.
"It's way past the time for our political leaders in Europe to explore effective alternatives to the war on drugs, which has been proved a catastrophic failure. Billions of dollars and millions of lives are at stake if they fail to act."