Medicinal plants (MP) have been used world-wide for the treatment or prevention of health conditions and due to their natural origin; they have been historically considered harmless. Semi-structured interviews were carried out with an intentional sample of twenty plant vendors in the city of Diadema to explore their knowledge and beliefs on the safety and efficacy of MP. Different levels of perceptions about the safety of MP were found, varying from "completely safe" to "completely harmful". The majority of the interviewees declared that "if herbs have an effect, they are also likely to have a side effect", depending on many factors such as dosage, concomitant use of other drugs, characteristics of the plant material and consumer related factors, specially those related to pregnant women, children and elderly people. Thirty-nine unexpected events related to 21 species of MP were reported. One case of serious gastrointestinal disease related to the consumption of a contaminated "slim mixture" was also described. Adverse events and other problems that result from MP are relatively uncommon, but they are almost certainly underreported and occur more often than acknowledged. This study strengthens the call for further research and educational efforts into this complex area.

A crença de que medicamentos à base de plantas são isentos de riscos à saúde faz parte da bagagem cultural da população afeita ao seu uso: "o que vêm da terra não faz mal". No entanto, o potencial tóxico, as características específicas do usuário, a possibilidade de contaminação e a falta de regulamentação constituem fatores de risco para a ocorrência de reações adversas, intoxicações e outras complicações decorrentes de seu uso. Foram realizadas entrevistas semi-estruturadas junto a 20 raizeiros (vendedores de ervas "in natura") na cidade de Diadema/SP. Foram relatados 40 casos de problemas relacionados ao uso de 22 espécies de plantas medicinais. As espécies mais citadas foram Luffa operculata - buchinha (7 casos), Senna alexandrina - sene (4 casos) e Paullinia cupana - guaraná (3 casos). Dentre os sinais e sintomas relatados, os mais freqüentes foram relacionados ao sistema nervoso central, problemas gastrointestinais e cardiovasculares. Os entrevistados também relataram um caso de aborto relacionado ao uso de S. alexandrina e três casos de óbito após a ingestão do chá do fruto de L. operculata. O caráter "natural" das plantas medicinais não é sinônimo de ausência de riscos para a população usuária. É necessária a implantação de políticas de fitofarmacovigilância eficientes, a fim de tornar o consumo mais racional e, deste modo, minimizar os riscos à população usuária.

Traditionally, medicinal herbs have been considered gentle and harmless because of their natural origin: "natural and therefore free of risks". However, toxic potential, various consumer-related factors (such as age, disease factors, pregnancy, etc), contamination, and lack of regulation concerning quality control are some of the risk factors deemed to be associated with herbal adverse reactions, poisonings and other complications. Over a 7-month period, semi-structured interviews were carried out with 20 "raizeiros" (traditional healers) in Diadema/SP. We found 40 unexpected events related to 22 species of medicinal herbs. The most frequent species reported were Luffa operculata - "buchinha" (7 reports), Senna alexandrina - "sene" (4 reports) and Paullinia cupana - "guaraná" (3 reports). Among the adverse events, the most frequent signs and symptoms reported involved the central nervous, gastrointestinal and cardiovascular systems. They also reported one case of abortion (related with S. alexandrina) and three deaths related with L. operculata. Adverse events that result from "natural" medicines are relatively uncommon, but they certainly occur more often than acknowledged. Medicinal plants are traditionally considered as innocuous, but as commercially available medicinal products they require sanitary surveillance in order to identify their risks, to give them a legal status, to evaluate their efficacy and to ascertain their safety.