Jeremy Corbyn would decriminalise cannabis for medicinal purposes, but would not support legalising recreational drugs.
He said the huge consumption of drugs in Europe and America has fuelled a "deeply nasty" narcotics trade elsewhere in the world.
Speaking at a Labour leadership debate in Glasgow, he said: "I would decriminalise medicinal uses of cannabis.
"I would also want to look at supporting people who want to get out of the drugs trade in other parts of the world because there is the horrors of the drugs war that's going on in Central America, and very large numbers of people who have died as a result of it."
He said there "has to be an intelligent approach to this."