Pope Francis, the first Pontiff from South America, criticised countries in Latin America that had declared the war on drugs could never be won and that some alternative to total prohibition must be found.
"A reduction in the spread and influence of drug addiction will not be achieved by a liberalisation of drug use, as is currently being proposed in various parts of Latin America," he said.
Instead it was necessary to confront the underlying problems of drug use and addiction, including "promoting greater justice" and "educating young people in the values that build up life in society".
Many countries in Latin America, where the decades-long fight against drugs has left tens of thousands of people dead or maimed, have proposed relaxing the blanket prohibition on illegal drugs.
Uruguay has spearheaded the movement, announcing last year plans to legalise sales of marijuana but under strict state controls.
Argentina, the Pope's home country, has moved towards decriminalising personal consumption of some drugs.
Brazil, which is hosting the Pontiff's week-long visit, has also partially decriminalised the personal possession of drugs. Fernando Henrique Cardoso, a former President of Brazil, has called for "an open debate on more humane and efficient drug policies". Costa Rica, Honduras, Mexico and Colombia have also relaxed their attitudes to personal drug use in recent years.
Last year Otto Perez Molina, the Guatemalan President, said that "drug consumption, production and trafficking should be subject to global regulations, which means that drug consumption and production should be legalised, but within certain limits and conditions".
