**6. The importance of medicinal plants used in traditional medicine in the development of orthodox drugs**

Historical experiences with plants as therapeutic tools have helped to introduce single chemical entities in modern medicine. Plants, especially those with ethnomedical uses, have been the primary sources of medicines for early drug discovery. A recent analysis by showed that the uses of 80% of 122 plant-derived drugs were related to their original ethnopharmacological purposes. Current drug discovery from terrestrial plants has mainly relied on bioactivity-guided isolation methods, which, for example, have led to discoveries of the important anticancer agents, paclitaxel from *Taxus brevifolia* and camptothecin from *Camptotheca acuminata* [30]. Plants contain thousands of constituents and are a valuable source of new and biologically active molecules [31].

About 25% of all prescriptions sold in the United States are from natural products, while another 25% are as a result of structural modifications of natural products constituents [6]. Furthermore, Farnsworth [6] claims that 119 characterized drugs are still obtained commercially from higher plants with 74% of them sourced from ethnobotanical information.

One of the most important areas of application of natural products is in the treatment of human and veterinary ailments. Currently, at least 119 chemical substances, derived from 90 plant species, can be considered important drugs that are in use in one or more countries [32]. Although, the use of natural products as medicinal agents presumably predates the first recorded history, as the earliest humans used various but specific plants to treat illness, the treatment of diseases with pure pharmaceutical agents is a relatively modern phenomenon [32]. Nevertheless, the role of traditional medicine in the discovery of potent chemicals is quite crucial. Among some of the earliest successes in developing drugs from natural products, are the reports of isolation of the antimalarial agents such as quinine, quinidine, cinchonine and cinchonidine from *Cinchona succirubra*. Currently, the hydroxychloroquine which is the derivative of quinine under investigation as a potential cure for COVID-19 [33]. Pain relievers such as the morphine from *Papaver somniferum* and acetylsalicylic acid from *Salix alba* [34, 35]. More recently, the vinca alkaloids: vinblastine and vincristine were isolated as antineoplastic agents from the Madagascan periwinkle (*Catharanthus roseus*), and subsequently derivatized to vinorelbine and vindesine, the drugs currently used for cancer treatment [32].

Similarly, a potent antimalarial drug, a sesquiterpenoid endoperoxide, artemisinin was isolated from *Artemisia annua* and is used as a remedy against the multidrug-resistant strains of Plasmodium. This followed the long use of this plant as an antimalarial drug in traditional Chinese medicine. Using the basic structure of artemisinin, semisynthetic compounds such as artemether and dihydroartemisinin were synthesized as potent antimalarial agents with the aim of optimizing the pharmacology of artemisinin. These are now in widespread use around the world [32]. Other drugs that were developed on ethnomedical information include reserpine, an antihypertensive agent from *Rauvolfia serpentina*, Atropine, an anticholinergic from *Atropa belladonna*, digoxin, a cardiotonic from *Digitalis lanata*, Physostigmine, a cholinesterase inhibitor from *Physostigma venenosum* and Ephedrine, a sympathomimetic from *Ephedra sinica* [36].

*Cultivation and Conservation of African Medicinal Plants for Pharmaceutical Research… DOI: http://dx.doi.org/10.5772/intechopen.102637*

These few accounts give not only the potential of plants as a source of drugs or as the solid link between folk medicine and drug development but also the necessity of research into medicinal plants [37].
