LA PAZ, Bolivia (REUTERS) - Pope Francis drank a tea of coca leaves, chamomile flower and anise seeds on the plane to Bolivia from Ecuador to ward off altitude sickness upon arrival at the highest international airport in the world.

Coca is the main ingredient for cocaine but people in the Andean region have chewed coca leaves or drank coca tea for centuries for its medicinal properties.

The flight attendant said the pope drank a mix called "Trimate," with the three ingredients. It was also offered to journalists on the flight.

The pope did not appear to have any diffficulties when he walked off the plane and while he was reading his welcoming address. Francis is visiting three of the poorest countries in Latin America on a trip that will also include Paraguay.

A Bolivian minister said 10 days ago that Francis had told government officials that he would like to chew coca leaves when he visits. A Vatican spokesman said, however, that the Argentine pontiff would decide for himself.

At just over 4,000 metres above sea level, La Paz airport is actually located in the appropriately named El Alto ("The High One"), a satellite city perched on the plateau above La Paz.

Indigenous people, including Bolivia's first indigenous president Evo Morales, defend the use of coca and consider it a sacred plant.

For health reasons, the 78-year-old Francis, who lost part of one lung to disease when he was a young man, will be in La Paz - 3,650 metres above sea level - for only about four hours before moving on to Santa Cruz.