The following is quoted from the book "Nomads of the Dawn". You will find information about this book at the end of the main text.
For the Penan the bounty of the rain forest is by no means limited to the foods they eat, or the plants they transform into tools and shelter. Perhaps the most remarkable evidence of their understanding and power of observation is found in their extensive use of medicinal plants.
In any area of the forest a Penan elder will readily find a score of healing agents- herbs and roots, the rhizomes of ferns, crushed leaves and the bark of trees and the lianas that hang from the heights of the canopy. Plants are administered as antidotes for food poisoning, contraceptives and abortifacients, clotting agents, general tonics and stimulants, disinfectants and to set bones, eliminate parasites, treat headache, fever, lacerations, boils, snakebite, toothache, diarrhea, skin infections and rashes. There are magical plants employed to dispel evil spirits, stop babies crying, or empower hunting dogs.
Many Penan medicinal plants have several uses. Getimang, for example, is one of the plants employed as an antidote to the dart poison. The petiole of the same plant is chewed as a treatment for stomach ache and indigestion. The leaves, heated over a fire, repel mosquitoes and keep bees away during honey gathering. The peeled inner bark is said to relieve headache when applied to the forehead. In the absence of a thorough ethnobotanical study, which has never been permitted by the Sarawak government, it is impossible to know which of these plants may be pharmacologically active and which mere supports for sympathetic magic.
According to the World Health Organization approximately 88% of the people in developing countries rely chiefly on traditional medicine for their primary health care needs. This high degree of dependence, together with many thousands of years of experimentation, have yielded numerous plants of true pharmacological worth. Seventy-five percent of the biologically active plant-derived compounds currently in use worldwide were discovered in a folk context, the gifts to the modern world of the shaman and the witch, the healer and the herbalist, the magician and the priest.
Plants are useful as medicines because they have evolved complex secondary compounds and alkaloids as chemical defenses against insect predation. These defensive chemicals, which in certain plants may comprise 10% of dry weight, interact harmfully with the biochemical apparatus of the insects. The same properties, however, can be exploited by science for therapeutic purposes. In seeking new medicines from the forest, the plant chemist, knowing that the difference between a medicine, a poison and a narcotic is often just a matter of dosage, is primarily interested in identifying any plant that is pharmacologically active. Any practical strategy for exploring the rain forest must include ethnobotanical work among the indigenous people who best understand this living pharmaceutical factory.
Tragically the medicinal knowledge of the Penan is being compromised at a tremendous rate. Logging activities are destroying the source of the medicines even as the forces of acculturation undermine the legitimacy and integrity of the folk tradition. Understaffed government clinics and itinerant physicians that make rare and brief appearances in the Penan settlements are no substitute for an ancient system of medicine, inspired by the spirit of plants and imbued by the people themselves with the power to heal.