If you're travelling through the Andes sooner or later you will become aware of people using coca leaves. You will see people standing or sitting by the side of the road or in parks holding a small plastic bag containing the leaves which they dip into every now and then and add a few more leaves to the wad already in their mouth. Our hotel in Potosi has coca leaves on the breakfast buffet and you can even get it in tea bags mixed with matte - a herb used to make tea. (Presumably it would be illegal for me to take some back home). Use of the leaves, which are the source of cocaine, is ubiquitous amongst the indigenous population but its connection to the hard drug (which they do not use) makes it controversial in some quarters.

Ostensibly coca is used because it is very effective against the effects of altitude but also because as a stimulant it helps to overcome fatigue, hunger, and thirst. However it has been a vital part of the religious cosmology of the Andean peoples from before the Incas through to the present. Coca leaves play a crucial part in offerings to the mountains and the sun and the earth. The leaves are also read in a way similar to the reading of tea leaves. It is an integral part of local people's way of life.

So any attempts to ban it are controversial. From 1961 the United Nations has declared cultivation of the coca leaf illegal and stated that its use should be phased out. Peru and, especially, Bolivia have campaigned against a blanket ban arguing that the leaf itself is not a narcotic and its use goes back centuries in traditional Andean communities. However as recently as 2009 the UN, under pressure from the United States (supported by the UK) rejected any change and countries such as Bolivia and Peru continue to come under pressure to eradicate its use. Judging from what we've seen on this trip those efforts are not having much effect.

And now you must excuse me. I'm just off to snort a tea bag.