Pope Francis warned against legalising drugs, calling addiction an "evil" which he said had to be resisted without compromise.
Setting himself against the trend in several western countries to allow the use of so-called soft drugs like marijuana, Francis said narcotics were putting more and more young people in danger.
"Drug addiction is an evil, and with evil there can be no yielding or compromise, he said in remarks to a drug enforcement conference in Rome carried on the website of Vatican Radio.
The remarks came a day before the pontiff is due to visit Italy's Calabria, home of the powerful 'Ndrangheta mafia, which controls a significant share of the global trade in illegal narcotics.
"Here I would reaffirm what I have stated on another occasion: No to every type of drug use. It is as simple as that," he said.
Francis, who has spoken out against drug use several times, said that to ensure young people did not fall prey to drugs, society had to say "'yes' to life, 'yes' to love, 'yes' to others, 'yes' to education, 'yes' to greater job opportunities".
"If we say 'yes' to all these things, there will be no room for illicit drugs, for alcohol abuse, for other forms of addiction," he said in remarks to a drug enforcement conference in Rome carried on the website of Vatican radio.
"The scourge of drug use continues to spread inexorably, fed by a deplorable commerce which transcends national and continental borders," he said.
The comments came as the state of New York prepared on Friday to pass measures that should lead to its becoming the 23rd U.S. state to allow medical use of marijuana.
Uruguay, which has already legalized the production and sale of cannabis, also said it would also allow doctors to prescribe the drug to treat certain conditions.
"Attempts, however limited, to legalize so-called 'recreational drugs', are not only highly questionable from a legislative standpoint, but they fail to produce the desired effects," the pope said.