The Vatican isn't ruling out that Pope Francis might chew coca leaves — or at least sip tea made from them — to fend off altitude sickness when he arrives in Bolivia next week.

Francis embarks on a South American tour Sunday that will take him to Ecuador, Bolivia and Paraguay. He is due to land Wednesday at La Paz airport, 4,000 meters above sea level.

Bolivian Culture Minister Marko Machicao told local media that Francis had asked to chew coca leaves upon arrival. Coca is legal in Bolivia and is considered a mild stimulant similar to coffee, but is banned by most nations because it is the raw material for cocaine.

Vatican spokesman the Rev. Federico Lombardi told reporters Tuesday: "The pope will do what he thinks is right."