Amazon hallucinogens make for cleaner living

Nicholas Schoon at the American Association for the Advancement of Science in Philadelphia on how natives use plant life against disease and predators

Hallucinogenic drugs from the Amazon rainforest are also a powerful medicine against gut parasites, a leading "ethno- botanist" and biochemist told the meeting. They are prescribed by tribal medicine men for both spiritual and medicinal needs, with no clear dividing line between the two.

Professor Eloy Rodriguez of Cornell University, New York State, studies the ways in which several tribes and animal species in a small part of the Amazon jungle in Venezuela use plants. In a series of field trips, he and his researchers have identified more than 100 species which are used for purposes other than food - deterring parasites and predators, fighting disease and putting people into a trance. The scientists then try to identify the cocktail of chemicals involved.

He has studied two plants which contain potent hallucinogens. One is a Passiflora or passion flower with large, beautiful red and yellow flowers, whose leaves are used to make a drink. The other is a legume called yopo which produces bean pods; native people grind the beans into a fine snuff then snort it.

Dr Rodriguez has tried them. "They have a very strong hallucinogenic effect but they're also very strong purgatives. Jesus! I lost 10lb in weight."

The chemicals involved are beta carbolines. They are able to "knock out" nematode worms which infest native peoples, paralysing them so that the diarrhoea and vomiting also caused by the medicine purge them from the body. The worms depend on serotonin, the "happiness" chemical used to signal between nerve cells, from their hosts to function normally. The carboline blocks their ability to use serotonin.

Tropical plants and insects contain a vast number of "secondary chemicals" which are used to deter predators. Native people have learnt to use them for making dozens of different poisons and medicines. Mammals scrape their fur with the bark or leaves of certain plants to keep pests off them, and eat others when they are sick.

Dr Rodriguez says he does not collaborate with Western drug firms prospecting for new materials because he believes native people will gain nothing. He says Indians must be encouraged to retain and spread their knowledge of the medicinal powers of local plants in their own countries, growing herb gardens.