Colombia's President Juan Manuel Santos signed a decree on Tuesday legalizing the growing and sale of marijuana for medical purposes, a dramatic shift in a country long identified with US-backed policies to stamp out drug crops.

Santos said the new regulatory framework was long overdue given that Colombians had been consuming marijuana and marijuana-based products in a legal void for years.

The new rules "represent a major step that put Colombia at the vanguard and forefront of the fight against illnesses", Santos said.