**3. Medicinal plants as therapeutic agents**

 Healing with medicinal plants is as old as mankind itself. The link between man and his quest for medicines in nature dates back to ancient times, when there were

 convincing proofs from written documents, monuments, and even original plant medicines [26]. Specifically, the oldest written evidence of usage of medicinal plants for preparation of drugs was found on a Sumerian clay slab from Nagpur, approximately 5000 years old. It comprised 12 recipes for drug preparation referring to over 250 plants [27]. Awareness of medicinal plants usage is a result of the many years of struggles against illnesses, which has prompted man to seek medicines in leaves, roots, barks, and other parts of plants [28]. The knowledge of the development of ideas related to the usage of medicinal plants, as well as the evolution of awareness, has increased the ability of health providers to respond to the challenges that have emerged with the spreading of professional services in the enhancement of man's life. Until the advent of iatrochemistry in sixteenth century, plants had been the source of treatment and prophylaxis for many diseases [27]. This is well exemplified globally where medicinal plants have always being an integral part of the health care system since time immemorial.

During the last decades, it has become evident that there exists a plethora of plants with medicinal potential, and it is increasingly being accepted that medicinal plants are offering potential lead compounds in the drug discovery process. In fact, the developed world has also witnessed an ascending trend in the utilization of complementary or alternative medicine (CAM) particularly herbal remedies [29]. While over 80% of the population in Sub-Saharan African countries like Nigeria and South Africa use herbal remedies for their primary health care, reports from developed countries such as Canada, Germany, and the US revealed that more than 70% of their populations have tried CAM at least once [29]. The most common traditional medicine in common practice across the globe is the use of medicinal plants. In most of the countries, medicinal plants are the most easily accessible health resource available to the community. In addition, they are most often the preferred option for the patients. For most of these people, traditional healers offer information, counseling, and treatment to patients and their families in a personal manner, as well as having an understanding of their patient's environment [30].

  Indeed, modern allopathic medicine has its roots in traditional medicine, and it is likely that many important new remedies will be developed and commercialized in the future from plant biodiversity, as it has been till now, by following the leads provided by traditional knowledge and experiences. The extensive use of traditional medicine, composed mainly of medicinal plants, has been argued to be linked to cultural and economic reasons. This is why the WHO encourages member states to promote and integrate traditional medical practices in their health system [31]. While a good number of plants (with only selected representatives listed here) have elicited significant therapeutic and pharmacological effects against well-known debilitating and degenerating diseases such as diabetes (*Artemisia afra, Chilianthus olearaceus, Vernonia amygdalina* [32], *Dicoma anomala* [33], *Psidium guajava* [34], and *Solanum incanum* [35]), cancer (*Taxus brevifolia, Podophyllum peltatum* [36], and *Catharanthus roseus* [37]), malaria (*Plumbago indica, Garcinia mangostana, Dioscorea membranacea, Artemisia annua, Piper chaba, Myristica fragrans,* and *Kaempferia galangal*) [38], HIV/AIDS (*Geranium phaeum*, *Sambucus racemosa* [39], *Tuberaria lignosa*, and *Sanguisorba minor magnolia* [40]), schizophrenia (*Abrus precatorius*, *Acacia ataxacantha, Adansonia digitata*, *Datura innoxia*, *Ficus sycomorus*, *Parkia biglobosa,* and *Ximenia Americana*) [41], tuberculosis (*Adhatoda vasica, Alpinia galangal,* and *Ocimum sanctum*) [42], microvascular and macrovascular disorders (*Anisodus tanguticus*, *Salvia miltiorrhiza* [43]*, Camellia sinensis*, *Castanospermum australe, Curcuma longa*, *Ocimum santum* [44]*, Stigma maydis* [45], *Spondias mombin*  [46], and *Gazania krebsiana* [47]), etc., studies are also in the forefront on the evaluation of plants against the neglected tropical diseases (NTD). **Table 1** presents some of the medicinal plants with reported significant efficacy against the NTDs.



**Table 1.** 

*Some selected medicinal plants used against neglected tropical diseases.* 
