Medicinal plants used in the Amazon region: a systematic review

The Amazon region’s biodiversity is exploited by the local population, commonly for therapeutic purposes. Given this information, the goal of this study was to perform a systematic review on medicinal plants used in this region, listing the name of the species, location found, and its importance for traditional medicine and for local people. For this, a search was performed in the PubMed/Medline and Lilacs databases, using the descriptors medicinal plants, Amazonia or Amazon region, in Portuguese, English, and Spanish. The main findings demonstrate that different species from different botanical families are used by the local population. The main therapeutic outcomes sought out refer to the search for relief or treatment of gastrointestinal, hepatic alterations, fever, kidney stones, pain, infections, and parasites. Thus, it is concluded that the practice of traditional medicine is very common in the Amazon region and is transmitted orally from generation to generation. In this practice, the use of medicinal plants in the form of tea is highlighted, with the species in the form of powder, dried or natural plants. Therefore, it is recommended that the strengthening of pharmacological studies involving local medicinal plants can provide scientific support for popular knowledge.


Introduction
The Amazon Rainforest is known as the largest forest on Earth and for sheltering the largest river basin in the world.
It is distributed by nine countries in South America, with the largest portion in Brazilian lands (67.8%), where it is called Legal Amazon and it comprises the states of Acre, Amapá, Amazonas, Maranhão, Mato Grosso, Pará, Rondônia, Roraima and Tocantins (Penna-Filho, 2013).
In addition to all its territory greatness, the Amazon has nine kinds of vegetation, of which Terra Firme Forest is the most important, since it covers 90% of the Legal Amazon and presents great variation of plant species that were not or are little explored (Braga, 1979;Penna-Filho, 2013), having them a great potential for generating resources, such as those related to the pharmaceutical and medical areas.
The potential of using medicinal plants as a treatment for diseases, called phytotherapy, is a practice of traditional medicine that has been used since the appearance of the human species (Badke et al., 2011), however, over the years and with the advance of technology, new ways to treat diseases were being developed and the use of medicinal plants became less common. Nevertheless, phytotherapy practice in Brazil has not lost its relevance despite the great incentives of the pharmaceutical industry in the country, due to folk knowledge about medicinal plants (Badke et al., 2011).
Additionally, with the advancement of Brazilian health models until the arrival of the Unified Health System, it can be understood that medicinal plants and herbal medicines have a lot to add in developing countries, as they are important instruments of pharmaceutical care, since 67% of medicinal plant species in the world originate from developing countries.
Since the past, several notices and resolutions of the World Health Organization (WHO) express the organization's position regarding the need to value the use of these drugs, in the health field, being observed as a normative basis for the maintenance of health (Unesco, 2020).
In 2006, the National Policy on Integrative and Complementary Practices was granted in order to establish guidelines and institutional responsibilities for the implementation/adaptation of actions and services in traditional Chinese medicine/acupuncture, homeopathy, medicinal plants and phytotherapy, in addition to establishing health observatories for social thermalism/crenotherapy and for anthroposophical medicine in the Unified Health System (Brasil, 2012).
In line with the above, in 2012, the Brazilian Ministry of Health launched the Primary Care Booklet 31, which guides the actions to be performed by the Basic Health Units and their professionals, in addition to making a historical overview of national policies and informing on the norms, guidelines, services and products related to phytotherapy in the Family Health Strategy/Primary Care. The objective of this is to implement new programs, improving the population's access to safe and quality products and services; sensitize and guide managers and health professionals in the formation and implementation of policies, programs, projects and structures that aim to strengthen phytotherapy, with an emphasis on primary care (Brasil, 2012).
In this context, since the Amazon Rainforest is a rich region with a large number of plants and phytotherapy practice is relevant in Brazil, the goal of this study was to perform a systematic review on medicinal plants used in this region, listing the name of the species, location found, and its importance for traditional medicine and for local people.

Methodology
The study is a systematic review of scientific articles on medicinal plants found in the Amazon region, which are used Research, Society andDevelopment, v. 10, n. 14, e163101419965, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i14.19965 3 in folk medicine; and it was made following the recommendation for PRISM reports of systematic reviews and meta-analyses (Moher et al., 2009).
Eligible studies were identified in searches carried out on July 4, 2019, in the PubMed/Medline (National Library of Medicine, Bethesda, MD) and Lilacs (Latin American and Caribbean Literature on health sciences) databases. The keyword combinations used in database searches, covering the Portuguese, Spanish and English languages, used in accomplishment researches were ("Plantas medicinais") AND ("Amazonia OR região amazonica"), ("Plants medicinal") AND ("Amazon OR amazon region") and ("Plantas medicinales") AND ("Amazon OR región amazónica"). In this research, all items were identified, regardless of study design.
The criteria for inclusion were data about the medicinal plants of the Amazon region, which are used by folk medicine for the treatment of diseases. Additionally, the exclusion criteria used were divided into three categories. First, data with a publication period before 2009. Second, review articles, historical documents, theses, and dissertations, considering only scientific articles. Third, escape from the theme of the present study, as well as data published without location information, locations outside of the Amazon region, lack of scientific names of medicinal plants and data that does not demonstrate the use of medicinal plants by population, with based on reading the title and abstract of the article.
The selected articles were evaluated by the reviewers considering the reading and careful analysis of the full text, by removing those who deliberate the exclusion criteria adopted. Still, the existence of data duplication in the same database and between databases was checked, and each item was counted only once. The information to be removed from articles included in the study were the names of plant species, the reason for its use, and how it was used, according to the Amazon region.
The results were described in a table, listing the characteristics of the botanical family, the plant species, the purpose of the study, the medicinal use, the form of preparation of the medicinal plant, the route of administration, the location found and the authors and year of the articles (Table 1).

Results
After the use of the above descriptors in the databases, 311 published articles were identified between January 1, 2009, and the date of search (July 4, 2019), of which 39 were repeated and were counted only once. After deleting them, there were 272 remaining items, of which 36 were not scientific articles. Then, reading the titles and summaries of other 236 articles, to identify which did not fit the criteria for inclusion, data about the medicinal plants of the Amazon region, which are used by folk medicine for the treatment of diseases. After this analysis, 51 items remained. With the reading of the articles in their entirety, there were 13 items left which were included in this review, because the others didn't bring the information about the medicinal plants of the Amazon region, which are used by folk medicine for the treatment of diseases ( Figure 1).
The results obtained regarding the botanical family, the main species, the purposes of the studies, the medicinal use, the form of use and the local application of medicinal plants in the Amazon region are listed in Table 1. Research, Society and Development, v. 10, n. 14, e163101419965, 2021 (CC BY 4.

Discussion
Ethnobotany is considered an important area of science, as it studies the ecological and cultural influences of plants from ancient and modern society, with great repercussions in pharmacology. In this context, ethnobotanical research extracts information about folk knowledge regarding plants so that studies that aim their beneficial use can be carried out. Thus, in addition to valuing folk knowledge, it can develop technologies to take advantage of these sustainable resources (Cragg;Newman, 2013).
One of the most important practices related to ethnobotany is called a blessing, which is a healing alternative practiced by women, usually called folk healers, who aim to heal through the use of plants and religion (Júnior et al., 2013). According to the evolutionary process, it is observed that women have most of the knowledge of the use of medicinal plants and, thus, the responsibility to take care of family health falls on them (Vásquez et al., 2014) Therefore, the main source of medicinal plants are the backyards of the houses, being them cultivated directly from the ground or flower beds, and, in the background, the forest also ends up serving as a means of access (Carniello et al., 2010).
In the Amazon region, which is home to various indigenous tribes, this practice is widely used by shamans, usually in rituals associated with supernatural factors. In addition to that, plants are also used as amulets, to scare the evil eye, during childbirth and religious rituals (Rocha, 2014). In this place, the knowledge related to the use of medicinal plants is orally transmitted from generation to generation (Freitas, 2014), that is, this knowledge is part of the culture of most people.
In this context, there are studies that indicate a national trend of deficit of scientific knowledge on the part of health professionals and the general population regarding Integrative and Complementary Practices, and a large part of pre-existing knowledge is conditioned to knowledge passed on through parental relationships and/or isolated events (Goés;Castro, 2019).
In this region, the main way of preparing medicinal plants is tea, which can be prepared in four main ways: (1) infusion, which consists of putting the contents of the plant in boiling water for 15-20 minutes, letting it rest for 5-10 minutes and then straining it is more used for the soft parts of plants, such as flowers or leaves; (2) decoction, which consists of placing the material in cold water and cooking it for 5-30 minutes and then straining it, is indicated for the hard parts of the plant, such as stems, roots, and barks; (3) maceration, which consists of placing the contents in cold water for 10-24 hours and then straining it is used for different parts of the plant, such as flowers, leaves, seeds, stems, roots, and barks; (4) herbal tea, which consists of placing the contents in a pan with boiling water for 5 minutes and then straining it, is used for herbs (Who, 2018).
Medicinal plants are often used in powder form, made from the dried plant, since crushing and sifting is necessary.
Then, this powder can be used to prepare infusions, decoctions, or oils. Besides, juices are also widely used, needing only to have its herbs crushed and then strained. Syrups are prepared with a mixture of 50% juice, decocted or macerated, and 50% honey. As a form of external use, poultice stands out, a form in which fresh or dried herbs are used, which is placed directly on the spot you want it. The bath is also an external use form, because despite being prepared from an infusion, instead of ingesting it, it is used to wash the body (Who, 2018).
Other ways of using medicinal plants involve inhalation, which consists of placing the contents in boiling water and slowly inhaling the released steam, and tincture intake, prepared as if it were a maceration, but using alcohol, preferably cereals, being consumed in drops diluted in cold water, ointments, or rubs. The tincture form is the one that most preserves the active principles of medicinal plants, since most are soluble in alcohol (Who, 2018).
Even with people's access to traditional medicine, medicinal plants are still widely used for maintaining health in some communities in the Amazon (Vásquez et al., 2014). In this study, the main botanical families used in this region were analyzed with Fabaceae being the most frequent, presenting species pointed out by the population as effective in the treatment of gastrointestinal alterations, it is usually used in the form of infusing or cooked (in the colloquial language) for cases of diarrhea and abdominal pain. In addition, they are species used to treat infections, inflammations, liver disorders, and even cancer (Frausin et al., 2015;Gois et al., 2016;Rengifo-Salgado et al., 2017) (Table 1, columns 1, 2, and 4).
The Euphorbiaceae and Rubiaceae families described in different studies are identified by the population as useful for liver, gallbladder, stomach, and kidneys' alterations relief, in addition to pain and fever reducing. These species are mainly used in the forms of decoction, macerated or infused (Odonne et al., 2013;Santos et al., 2014;Castillo, 2015;Giovannini, 2015) (Table 1, columns 1, 2, and 4).
Species of the Solanaceae Family are listed by the population as effective for treating rheumatic alterations and reducing fungal infections. The main ways of preparing and using these species are tea, juice, poultice, and tincture (Polesna et al., 2011;Castillo, 2015;Gois et al., 2016) (Table 1; columns 1, 2, and 4).
The Rhamnaceae and Apocynaceae families present botanical species used by the population for the treatment of malaria, that represents an endemic disease for the Amazon region which can be explored by parasitic research groups, so that better therapies against it can be developed (Oliveira et al., 2015;Veiga et al., 2015;Gois et al., 2016) (Table 1; columns 1, 2, and 4).
Other botanical families were listed by the Amazon region population and were used for intestinal and respiratory disorders, anemia, headaches, and fever, among others (Table1). This knowledge, full of inaccuracies, especially with regard to the method of preparation, indications and scope of the use of plants and herbal medicines, can lead to treatment failure, leading to a future disbelief in the use of this type of treatment by the patient. Léda;Oliveira, 2018).
Folk knowledge about medicinal plants has awakened governmental interest, a fact that has supported policies that aim to highlight the importance of alternative medicine for more effective and humanizing health care (Brazil, 2000). The demand for PICS has increased due to its power to guide the doctor-patient relationship as an important element in therapy, it values simple therapeutic forms, it is less dependent on technologies, and increases the patient's autonomy over the healing process itself (Levin et al., 2001;Nogales-Gaete, 2004;. Folk medicine study, especially of herbal medicines, has received greater attention from pharmacological research, as they have provided science with a greater amount of information regarding active principles (Vale, 2002). In this sense, folk knowledge provides the basis for advances in the fields of therapeutics, emphasizing the importance of updates on traditional medicine.
The limitations of the study involve the difficulty of obtaining more complete information about the plant species used in the Amazon region in published articles, in the sense of correlation with therapeutic use, the chosen plant parts, forms of preparation, route of administration, among others.

Conclusion
Traditional medicine, practiced through the use of medicinal plants, proves to be of great importance for the Amazon region population, so much so that it is a factor present in the culture of these people and that is passed on from generation to generation. This proves how important this practice is for complementing official medicine. In this sense, it is concluded that the practice of traditional medicine is very common in the Amazon region and is transmitted orally from generation to generation. In this practice, the use of medicinal plants in the form of tea is highlighted, with the species in the form of powder, dried or natural plants. Thus, this study serves as a basis for more in-depth pharmacological investigations to be developed based on the information cited. Therefore, it is suggested that the strengthening of pharmacological studies involving local medicinal plants can provide scientific support for popular knowledge.