Modern medicine owes to tradition the possibility of knowing plants. The medicinal principles were isolated and were investigated because of plant tradition.
Among the most popular example, we can mention the case of aspirin. The bark of white willow (Salix alba) was already used in China over 2500 years ago to reduce fever and relieve pain.
References about this plant appear in the work of Hippocrates (400 BC.) who recommended it for the same disorders. Dioscorides (40 - 90 AD) added a new use and advise on the treatment of arthritic pain. The use of this remedy leaves no traces in the Middle Ages.
In 1763 Edward Stone, an English clergyman, wrote to the Royal Society on the importance of this plant in pain relief. In 1835 the German chemist Karl Jakob Lowig discovered that one plant produced the same results: meadowsweet (Spiraea ulmaria = Filipendula ulmaria) contained the same principle that white willow: salicylic acid.
It was not until 1893 that Felix Hoffman synthesized the derivative of this principle trying to alleviate the side effects produced by salicylic acid in the stomach of his father who used it to relieve his arthritis.
Aspirin, acetylsalicylic acid, a derivative of salicylic acid is the most common analgesic and the most used and best selling to date. It was the traditional knowledge of the properties of willow which led to further scientific research that has permitted the production of aspirin.
The wealth of the tropical forest
Besides aspirin, another series of very important principles were discovered researching the use of certain plants that traditional cultures made in different continents since ancient times.
An estimated 120 pharmaceutical products are directly derived from medicinal plants.
It is also believed that 25% of current drugs contain some principle derived in the past or derived directly from medicinal plants. In particular, the contribution of tropical forests in the discovery of new drugs has to be remarked, to the point that 75% of medicines derive from plants that can be found in these forests.
The explanation of this fact lies not only in the fact of the extremely rich vegetation of this biotope, but to the fact that this is where the plants have to develop major defense mechanisms against their many predators (viruses, fungi, insects, higher animals, herbivores).
It is struggle for survival, along with the development of certain colors, aromas, etc. designed to attract the attention of pollinators or seed dispersal, what has led to the development of an entire chemical arsenal by the tropical forest plants.
Where are the active principles of the medicinal plants placed?
The active ingredients of medicinal plants may occur throughout the plant, but generally, the roots and bark have the highest levels. Flowers, seeds or fruit parts would contain many of them.
These principles may vary throughout a species and on plants of the same species according to many factors: time of year, soil characteristics, etc.
The stimuli a plant is subjected is very important to increase the levels of certain components. It has been proved that the administration of certain substances (elicitors or triggers) can increase their proportion.
For example, in experiments on willow (Salix alba), the artificial infection of the plant with bacteria produces higher levels of salicylic acid.
The discovery of the active principles
Modern medicine is based on clinical testing. Clinical experimentation has managed to clarify the validity of those plants that had been being used under a traditional basis of trial and error.
Many of them proved to be valid, others proved to be harmless, others potentially dangerous. Modern biochemical assays have been able to determine which are the main components of the so-called active principles of medicinal plants .
The capacity of the modern chemical industry to produce these principles without the aid of the plants does not suppose to deny the importance that medicinal plants have had in the past and will have in the future (More information on the importance of medicinal plants)
The main chemical constituents of medicinal plants could be classified into the following groups: