**5. Secondary metabolites**

The pharmacological activities of HMs are responsible for their benefits and for most of their toxicities. These bioactivities are essentially due to the presence of certain complex chemical entities: the secondary metabolites [21, 22]. While some are responsible for the radical active actions, others act as buffers which modulate and modify the pharmacological actions produced by active components to make them less toxic or more active. This is probably responsible for the reason why several plant extracts or recipes may not be reproduced by the isolated purified chemical constituents of the herb or recipe [23]. The various complex compounds elicit a long range of different activities in man and, animal models and cell cultures. In many instances the degree of activities of the active secondary metabolites vary depending on such factors as the plant species, parts of the plant, geographic origin, time of collection, method of preparation, amount ingested, and so on.

where conventional healthcare is available and easy to access. Also, in the USA, about 40% of the adult population has used herbal medicine [27]. The sales output of HM in Canada [28],

Introductory Chapter: Introduction to Herbal Medicine http://dx.doi.org/10.5772/intechopen.78661 5

In recent times, the popularity and use of HMs have cut across geographical, gender, economic and socio-cultural divisions. Indeed, HM is occupying a strategic position in the general healthcare of people worldwide. Some of the probable reasons adduced for this include:

The use of HM is an age long tradition which is enshrined in the culture of many societies. In past times, people have relied on it as their primary source of healthcare with much success. Despite modernization and the proliferation of conventional healthcare that hinges on the use pharmaceutical drugs. Some people especially in Africa and Asia still lay personal preferences on HM: this group of people will always prefer HM as their first line of therapy

Generally, many lay users have the opinion that HMs are safe and carry no risk or side effects. Though HMs are natural products derived from plant materials, minerals and some animal matter, this belief is nevertheless erroneous as many HMs are not totally devoid of adverse effects. While, it is true that many HMs are comparatively more tolerable than pharmaceutical drugs especially in long time use for the management of chronic ailments [30, 31]. Studies have shown that in some countries such as South Africa and Ghana, herbalists far outnumber the conventional medical doctors, whereas in India, China, and Vietnam, the number of herb-

Especially in rural African and Asian communities where access to conventional medical services is either expensive or difficult the only reliable, easy and quick access to healthcare is the traditional medical practitioners (TMPs) whose therapy is always based on HM. Even in societies where pharmaceutical products are highly regulated, HM is easily obtained at low

In many rural communities, the cost of HMs is often low when compared to those of the conventional medicines. The TMPs who provide the services are usually community members who often live in the neighborhood of their clients (patients), as against the long distances to be traversed to reach the conventional medical centers. Most HMs are extemporaneously

whenever possible irrespective of their economic, educational and social status.

Australia [6] and Europe especially in Germany and France is rapidly increasing [29].

**7. Reasons for the upsurge in the use of HM**

alists and the conventional doctors are comparable.

**7.1. Personal preferences for HM**

**7.2. Perception of safety**

**7.3. Easy accessibility**

**7.4. Low cost**

cost and without prescriptions.

Plant secondary metabolites (PSM) are a large group of compounds that are synthesized and concentrated optimally in certain plant species and organ. The primary functions of these compounds in the plants in which they occur includes defense against such adversaries as herbivores, bacteria, fungi and viruses. Many also show variable degrees of antioxidants and UV protectants effect against harmful elements [24], while some also play important roles during pollination (to attract pollinating and seed-dispersing factors or signaling agents. This wide group of chemicals contains reactive functional groups in their chemical structures that are capable of forming covalent bonds with other biocompounds such as proteins, peptides and sometimes DNA [23].

PSMs are primarily organic compounds and can simply be grouped into three major classes, terpenes: volatiles, cardiac glycosides, carotenoids and sterols; phenolics: phenolic acids, coumarins, lignans, stilbenes, flavonoids, tannins and lignin; nitrogen containing compounds: alkaloids and glucosinolates [25].
