It was community based cross-sectional study that involved an in-depth ethnobotanical survey. Both quantitative and qualitative study designs were carried out using a semi-structured in-depth interview.

The study was carried out in Goma city, capital of NK province in eastern DRC. Based on its geographic coordinates, Goma is located between 1041’S latitude (−1.6771 degrees minutes) and 29,015’E longitude (29.242 degrees minutes) [19]. Its altitude is estimated at about 1500 m above sea level and has an area of 66.45 km² covered by volcanic rock with undulated reliefs at about 18 km from Nyiragongo volcano [20]. The area is characterized by savanna tropical climate influenced by high altitude. The annual minimal and maximal average temperatures, as well as annual amount of precipitation are 14.03˚C, 25.5˚C and 1257 mm respectively. Overall, the city has a multi tribal population of 1.1 million urban habitants [21].

Regarding administrative organization, Goma city includes two communes; commune of Goma and commune of Karisimbi subdivided into 7 and 11 quarters respectively (Figure 1). Each quarter is subdivided into cells with several streets. The commune of Goma is located in the south of Goma city and has an area of 28.754 km². It hosts almost all political administrative and economical quarters. While the commune of Karisimbi is located in the north of commune of Goma and has an area of 37.698 km². The commune is essentially residential and has population of 622,105 habitants with low income [20]. So, individuals from Karisimbi were used as key informants to select THP key informants.

Data on indigenous use of MP in management of MIs and related symptoms was collected in two communes for some reasons, including: 1) Their location near Virunga National Park rich in biodiversity; 2) Goma city has been the theater of war for more than 20 years that has disorganized government general health care [22]; 3) Several studies conducted in Goma city have reported the use of herbal medicines. Overall, among previous studies done on herbal medicine in Goma city none cover specifically MIs and related symptoms.

The sample size was determined using a single proportion formula, n₁ = z²p (1 − p)/d²,

where n₁ was the initial sample size (n₁ = 376.48), considering a confidence level of 95%, an overall proportion of good knowledge of population of Goma city about THP dealing with MIs of 50% estimated on basis of pilot study [24], and a precision of 5%.

We performed a finite population correction, n₂ = n₁/1 + (n₁/N), where N was the total number of a targeted population including male and female respondents aged 18 years and above, non THPs and non-healthcare practitioners (HCP) of commune of Karisimbi. Thus, we computed N = 343,278 according to INS-North-Kivu [20] and we obtained n₂ = 376.07. Multiplying n₂ by 1.5 to account for the clustering effect, and adding a 15% non-response rate, we obtained a final sample size of 620 key informants.

Sampling procedure of the key informants included geographical cluster and stratified random methods. Age-order method was used to identify the potential respondents in households [25], and no replacement was made. The key informants consenting to the objective of the study were used to select THPs dealing with MIs in Goma city.

We defined a THP according to the Congolese [26] law on traditional medicine(TM). It has been reported that among THPs, herbal therapists are reputed to have in-depth knowledge on local plants. However, each of them has its own field of expertise and the techniques as well as MPs employed in management of various ailments differ considerably [27]. Thus, snowball ball sampling method was used to select male and female THP dealing with MIs and consenting to participate in the study.

Also, it has been reported that in qualitative study, data collection is based upon a saturation point judged by researcher to give best information [28]. Thus, sample size of THP key informants included total number of all those who were appointed by the 620 key informants as dealing with management of MIs in Goma city.

Firstly, permission to collect data from individuals in Goma city was got from the Directorate of Health Services. Secondly, permission was got from administrative leaders before any interaction with prospective respondents. Thereafter researcher interacted with prospected respondent following two steps; especially: 1) Interaction with each selected 620 key informants to select THP key informants; 2) Interaction with each THP key-informant for in-depth ethnobotanical survey. Overall, researcher started their interaction with each prospective respondent by first explaining the aims and objectives of the project in order to solicit their consent and cooperation before any data were gathered. We used face-to-face interview to interact with all respondents recruited in the study. Then, voucher specimens were collected, identified and allocated a number by a taxonomist at Makerere University National Herbarium (MHU), Kampala.

Regarding data collection tools, for quantitative study, data related to 620 respondents in local communities were collected through face-to-face semi-structured in-depth interview by using interview schedule translated into French and local language (Kiswahili). The interview schedule included 2 domains especially socio-demographic and knowledge of THP experts in management of MIs in Goma city. For qualitative study, data from THPs were collected through an interview guide translated into French and local language (Kiswahili). The interview guide related to THPs had 5 themes including, socio-demographic theme, MPs used in management of MIs (plant name, part of plant used, treated MIs, method of preparation, route of administration, tratment duration), method of diagnostic, how to recognize healed patient and source of knowledge.

Both adult male and female individuals aged between 18 years and above, non THPs and non allopatic health care practitioners, residents of Karisimbi commune and consenting to participate in the study were recruited in the study. The recruited individuals were aked to nominate THPs dealing with management of MIs in Goma city. Both male and female THPs appointed by individual in community as dealing with management of MIs, resident within Goma city and consenting to participate in the study were selected for interview. Individuals and THPs who were below 18 of age, did not consent to the study, and those who were absent at the time of data collection were excluded from the study.

Excel 2016 was used to process the data. Quantitative raw data were cleaned scrutinizing the completed research instruments to identify and minimize, as far as possible, errors, incompleteness, misclassification and gaps in the information obtained from the respondents. Having cleaned, the data were coded following the process including developing code book, pretesting the code book, coding the data and verifying coded data. The data base information necessary to answer our research questions were exported to SPSS 2017 statistical package for analysis.

Qualitative transcribed data using Microsoft Word 2018 were closely studied according to the following steps: 1) Identifying the main themes communicated by respondent; 2) Assigning codes to the main themes; 3) Classifying responses under the main themes; 4) Transformation of qualitative data into quantitative data for analysis of responses of main themes.

Use value (UV) parameter was calculated according to the formula of Phillips et al. [29] and Thomas et al. [30] to determine the relative importance attached to a given MPs species in TM of Goma.

UVs = ∑ i = 1 n Uis ns (1)

In which UVs is the use value of a given species s; Uis is the number of uses of species mentioned by informant i; ns is the total number of informants.

Since it has been reported that UVs parameter does not reflect the consensus of informants on MPs use, we also calculated for each species, the parameter informant agreement ratio (IAR) [31] [32] [33].

IAR = Nr − Na Nr − 1 (2)

In which Nr is the total number of citations of the species and Na is the number of diseases treated by the species.

Informant consensus factor (ICF) was calculated for each plant use according to Trotter and Logan formula [31], to verify informant agreement for a plant species in the treatment of a particular MI and to select species with an interesting therapeutic potential for phytochemical and pharmacological studies.

ICF = Nuc − Nt Nuc − 1 (3)

In which Nuc is the number of citations of a particular MI; Nt is the number of species used for the treatment of that MI.

Species therapeutic potential (STP) parameter was calculated according to Heinrich [34] to select plant species that seemed to be potentially effective for treating MIs and therefore merit phytochemical, pharmacological and toxicity studies. We considered species with high STP% as potentially effective.

STP % = Ni − 1 Nti (4)

In which Ni is the number of informants who mentioned the use of a species for the treatment of a given MI, and Nti is the total number of informants who mentioned any species for the treatment of that MI.

Medicinal plants were considered as priority for a MI if they had the highest UV, IAR, and STP% values, also, if not much was known about their anxiolytic and antidepressant activities as well as toxicity profile in laboratory animal models.

Quantitative data from both quantitative and qualitative studies were expressed as frequency, displayed in tables and graphs. Non parametric tests including Mann-Whitney [35] and Kruskal-Wallis [36] were performed to assess whether or not significance difference exists in MP knowledge between the two genders, and different religion groups. The correlation coefficient of Spearman was calculated to elucidate if there were a correlation between informants’ age, experience, source of knowledge, education level and their knowledge on MPs. Results of Mann-Whitney, Kruskal-Wallis and Spearman correlation tests were considered as statistically significant for p values < 0.05.

To find out the percentage of common use of plants species for MIs treatment between THPs of commune of Goma and THPs of commune of Karisimbi, the Rahman’s similarity index (RSI) was used, which indicates the similarity of species used for treating the same MIs [37]. Thus, THPs of the two communes are closer in treatment of MIs if they use the same species in their management; hence, RSI > 50%.

RSI = d | a + b + c − d | (5)

In which “a” is the number of unique species in commune of Goma, “b” is the number of unique species in commune of Karisimbi, “c” is the number of common species in both communes Goma and Karisimbi, and “d” is the number of common species in both Goma and Karisimbi that are used to treat the same disease; a and b ≠ 0 and c and d ≥ 0.

Also, Frequency index was used to find out the commonality of plant species. A plant species was considered as common when its FI was >50%.

Socio-economic and demographic characteristics of respondents are sammurized in Table 1.

A total of 30 plant species, distributed in 29 genera and 19 families were inventoried. Families representing most species were Asteraceae, Lamiaceae and Solanaceae (4 species i.e., 13.80%). While the other 16 families were represented by 1 or 2 species (Table 2).

From total number of 30 plants species, 19 (63.33%) were reported for anxiety and related symptoms, 11 (36.67%) were reported for psychosis and 9 (30%) were reported for depression (Figure 2). Leaves (90%), decoction (46.67%), oral ingestion (73.33%), wild (53.33%), <1 month (73.33%), were the most frequently cited plant part, method of preparation, mode of administration, place of collection and treatment duration respectively (Figure 2).

None of 30 MPs was reported with the majority (FI < 50%) of respondents (Table 2). However, high similarity (RSI = 77.42%) was observed in the use of common species for MIs between THPs key informants from both Goma and Karisimbi communes.

Training was reported by more than half (>50%) of THP as source of TMK. While inheritance from forefathers was reported by 23.26% of THP as source of TMK. Patient’s story (60.46%) and absence of MIs crisis (58.14%) were most reported methods of diagnosis and recognition of healed patient respectively.

There were no statistically significant differences (p > 0.05) between gender and Goma city TMK (based on number of reported medicinal species for depression, anxiety and psychosis). Also, there were no statistically significant differences (p > 0.05) between religions and Goma city TMK on MPs used for depression, but there were statistically significant differences between religions and Goma city TMK on MPs used for anxiety and psychosis. Positive Spearman correlation (p < 0.05) were found between experience and age as well as experience and TMK on MPs used for depression, anxiety and psychosis (p < 0.05). Also, positive Spearman correlation (p < 0.05) was found between source of knowledge from forefather and TMK on MPs used for depression. Nevertheless, training and education level did not influence TMK (p > 0.05).

This study documented many plant species distributed in various families used as indigenous herbal medicines for management of MIs in Goma city. The families representing most species used in management of MIs included Asteraceae, Lamiacea andSolanaceae.

The frequent use of plant species of Asteraceae family in TM of the Goma city to treat MIs is probably due to their psychopharmacological activities. Indeed, according to Guenne et al. [38] plant species of Asteraceae family have phytochemical compounds that would have cholinergic, dopaminergic or serotoninergic system actions, which are major systems involved in the manifestation of neuropsychiatric disorders.

Plants species of Lamiaceae family are most used in TM of Goma city probably due to its pharmacological importance reported by Farzaneh et al. [39], especially their neurotropic activity as reported by Zvezdina et al. [40].

The explanation of the widespread use of species belonging to the Solanaceae is probably related to the fact that the family is source of tropane alkaloids including atropine, hyoscyamine and scopolamine, that are among the oldest drugs used in medicine due to their anticholinergic activity [41] [42]. Also, various pharmacological studies have demonstrated anxiolytic and antidepressant activities of species of Solanaceae family [43]. However, Solanaceae is comprised of several species that are toxic, and sometimes lethal to mammals, in particular to man [44].

Despite the fact that none of 30 MPs was associated with high FI >50%, high RSI was observed in the use of common species for MIs between THPs key informants from both Goma and Karisimbi communes.

The similarity of the use of common species for MIs is probably explained by the fact that training was reported as common source of knowledge by majority of THPs. Additionally, the high RSI may be linked to the fact that the two communes belong to the same phytogeographical environment and share more or less the same ecoclimatic and edaphic conditions and common realities [20].

Findings revealed that MPs used for anxiety were the most frequently cited than those used for psychosis and depression probably due to the fact that anxiety is one of commonest MIs in regions affected by war conflict such as NK as reported by WHO [4].

The majority of plant species used for psychosis are also used for anxiety. This is because the management of psychosis requires sedation for patient presenting agitation. It has been reported that some anxiolytic conventional drugs such as benzodiazepines decrease acute psychosis and have proven efficacy for agitation [45]. Also, it is established that atypical antipsychotic drugs possess multimodal mechanism of action including modulation of serotonin (5-HT), norepinephrine, histamine neurotransmission that underlies their benefs in mood and anxiety disorders [46]. However further studies are needed to elucidate the efficacy of these plants in anxiety and psychosis.

Leaves, decoction and oral ingestion were the most reported plant part used, method of preparation and mode of administration respectively. The preference medicinal use of leaves could probably be because they are easily and conveniently harvested [47], also they are the site par excellence of biosynthesis and storage of secondary metabolites, responsible for biological plant properties [48] [49]. Oral route is most preferred in TM of Goma Goma city probably due to the fact that it is noninvasive, high patient compliance, convenient to handle and does not require any specific conditions [50]. Decoction is used as method of preparation of most MPs for MIs in Goma city probably due to its easy preparation processes and probable ability to enhance the dissolution of some bioactive compounds compared with other methods of preparation such as maceration [51]. Wild MP collections were the mostly used in management of MIs due to the fact that overall DRC is rich in natural forests with various MPs [17] but also, probably due to the location of Goma city near Virunga national park reach in biodiversity. Overall, the duration of treatment of various MIs in TM was shorter (<1 month) than that recommended by guidelines for pharmacotherapy of those ailments [52] [53]; due to claim that MPs might be most efficacious than conventional drugs [18]. However, experimental studies are needed for evidence of this claim.

Euphorbia abyssinica, D. adscendens, C. gynandra andS. macrocarpon were reported as the most important MPs for anxiety in traditional medicine of Goma city Pharmacopeia. Also, C. sumatrensis, E. coccinea and C. basilicum were reported in the study as the most important MPs for depression in TM of Goma city Pharmacopeia. However, C. rubiginosa, D. adscendens, P. edulis, andA. Sieberiana represented the species with the highest level of consensus for their use by THP as remedies for anxiety.

Indeed, the present study analysis demonstrated that E. abyssinica had highest STP%. Latex from E. abyssinica has been reported to have antibacterial and antifungal activities [73]. The medicinal effects of the plant are mainly confined to its latex and roots [74]. However, it is rather classified as a poisonous plant by the Food and Drug Administration of the United States of America [75] and no much is known on its use as drug against MIs. Pharmacological and toxicological studies are needed to justify its use against MIs in TM of Goma city.

Desmodium adscendens is a plant which has been scientifically proven for its diverse positive CNS pharmacological activities. Its ethanolic extract has been proven to induce hypothermia, possessed analgesic effect and reduced the tonic phase of convulsion, and eventually mortality in PTZ-treated mice [76]. According to the authors, the plant species extract might act through the opioidergic, adrenergic systems, adenosine triphosphate (ATP)-sensitive K+ channels, and the serotoninergic pathways to ameliorate pain in murine models that probably explain its use as MIs therapy in TM of Goma city.

Several research reveal that C. gynandra possesses a huge range pharmacological applications, including anti-inflammatory, free radical scavenging, as well as its analgesic activities [77] [78]. Also, scientific perusal reveals that different parts of the plant are of immense medicinal importance which may prove its traditional use in DRC. Among species of Cleome genera, studies conducted by Sana et al. [79] and Tabariyeng [80] concluded that Cleome brachycarpa possesses anxiolytic and CNS depressant effect after acute dosing. Despite its high SPT% revealed by this study, to date, there is not much research investigation for pharmacological importance of C. gynadra for MIs. Thus, psychopharmacological studies are suggested to explain its use in management of MI in Goma city.

Study conducted by Eletta et al. [81] and Ozioko and al. [82] showed that the aqueous extract of S. macrocarpon leaf has dependent significant antioxidant property on the experimental rats. Also, the study conducted by Oluwagunwa et al. [83] revealed the antihypertensive activity of the plant species in rats due to activities of renin and angiotensin converting enzyme to varying extents. Psychopharmacological study of the plant species was also suggested to elucidate its use in TM of Goma city as therapeutic agent against MIs.

Conyzasumatrensis has demonstrated antimalarial activity through in-vivo evaluation in Plasmodium berghei infected mice through the study that was conducted by Pone and Anirba [84]. The study conducted by Olapeju et al. [85] showed antimicrobial activity of the plant. However, no literature was found regarding its antidepressant activity.

Simplice et al. [86] reported neuroprotective and memory improvement effects of E. coccinea in animal models. Thus, the folkloric usage of this plant for the treatment of MIs is probably justified by those previous studies.

The indigenous use of O. basilicum in management of MIs in Goma city is probably supported by varieties of experimental models that has demostreted the CNS depressant and anticonvulsant activity of the essential oil of the plant species obtained from leaves. According to Khair-ul-Bariyah et al. [87], the CNS depressant activity could be mediated by central GABAergic receptors.

Regarding plant species with highest level of consensus for anxiety, C. rubiginosa root extract possesses stimulant CNS function suggested by decreasing exploratory actions, its methanol root extract comprises saponins that exhibit powerful sedative action and also suppress spontaneous motor action in mice [88]. The study conducted by Xirui et al. [89], suggested that P. edulis possess antidepressant activity related exclusively to regulate serotonergic and dopaminergic transmission such as 5-HT, catecholamine and D₂ receptor. Akasiasieberiana has been reported to possess anti-inflammatory and anti-nociceptive pharmacological activities. According to Archer et al. [90], its anti-nociceptive effect may relatively be attributed to interactions with muscarinic cholinergic, adenosinergic and opioidergic system. The study revealed that the plant species possesses anxiolytic and sedative activities.

Medicinal knowledge

There were no statistically significant differences between gender and Goma city TMK. This finding is contradictory to previous studies showing that, in general, women know more than men about MPs [91]; some authors suggest that this is because men are more exposed to losing ethnobotanical plant knowledge than women [92]. Women’s work activities in home gardens and as primary family health caregivers might explain this literature finding [93] [94]. The explanation of the finding from Goma city is probably residing in fact that more than half (55.56%) of THPs, have their source of TMK from training that might be the same for both sexes.

Statistically significant differences between religions and of Goma city TMK Goma city for anxiety and psychosis may be explained by the fact that majority indigenous African communities believe that most cases of MIs have supernatural causes such as sorcery, curses and punishment from the deity [95]. According to IRBC [9] many Congolese believe in religion for treatment of MI.

Positive Spearman correlations were found between experience and age as well as experience and TMK for depression, anxiety and psychosis. Elders THPs tended to gain experience and to know more about MPs than younger THPs. Several other authors found the same tendency in their studies about MP knowledge in different parts of the world [96] [97] [98]. Reasons are that with progressive age, people have more time to accumulate knowledge and, therefore, show greater MP knowledge than the younger generation [99]. Other authors associate the lesser knowledge in the younger population in ongoing socio-economic and cultural changes [100].

Also, positive Spearman correlation was found between source of knowledge from forefather and TMK. According to some authors, TMK is mostly tacit in nature and is passed on from one person to another [101]. Elders are considered to be the legitimate custodians of this knowledge which was handed down to them by their ancestors, and they are in turn expected to pass it on to others [102]. This probably explains the fact that TMK of Goma city is most influenced by forefather’s knowledge.

Finding of the study revealed that training and education level did not influence TMK for depression in Goma city. The same result has been linked to that rapid socio-cultural changes due to globalization processes. Increased accessibility to health centers and improved transportation infrastructure result in a loss of ethnobotanical knowledge [103]. Additional explanation regarding TMK of Goma city is probably the lack of integration of TM in general curriculum of education of DRC.