Two decades of Mexican ethnobotany and research in plant drugs.

A renewed interest in the systematic study of indigenous medicines and associated medicinal plants arose in the 1970s. In Mexico the government established a national pharmaceutical industry to make use of the valuable colonial heritage of traditional practices combined with European medical concepts and resources. In 1975 the Mexican Institute for the Study of Medical Plants was created to integrate botanical, chemical and pharmacological studies on the Mexican flora. It compiled a database on ethnobotanical information relating to Mexican medicinal plants from the medical literature of the 16th to 19th centuries. A second database contained information on medicinal plants in current use. A medicinal herbarium was established. Taxonomical studies led to classification of the 11,000 voucher specimens in the herbarium and cross-referencing of the information with other databanks. A core group of 1000 plants used in traditional medicine throughout Mexico for almost 400 years was identified. Most of these are used to treat common diseases or basic health problems, usually given orally as decoctions or infusions. 95% of the plants used traditionally are from wild species. Information was collected from almost 3000 small Indian communities over four years on three aspects of traditional medicine--the healer, the disease categories recognized and the therapeutic resources in use. Plants with reported medicinal activity were selected for laboratory screening according to the frequency and commonality of their use, geographical distribution and seasonal availability. Screening involves a collaboration between chemists and pharmacologists: plant extracts are sequentially assayed and fractionated until the pure compound is isolated. Several active compounds are usually obtained from the same extract, frequently from the aqueous fractions. Ethnomedical information influences which plants are selected for screening and the type of assay used.