Medicinal plants have been serving as the major sources of medicine for maintenance of health and wellbeing of the human beings from the very beginning of their existence on earth. These medicinal plants were used by the early man, as are done now, in a variety of forms, such as in the entire form, and as powders, pastes, juices, infusions and decoctions for the treatment of their various diseases and ailments. These various converted forms of the medicinal plants may thus be very conveniently and genuinely called medicinal preparations or medicaments. This way, the medicinal plants formed an integral part of the health management practices and constituted important items of medicines from the very early days of human civilization. In the course of their traditional uses, the medicinal plants have contributed substantially to the gradual development of medicines to their present state.
As therapeutic uses of plants continued with the progress of civilization and development of human knowledge, scientists endeavored to isolate different chemical constituents from plants, put them to biological and pharmacological tests and thus have been able to identify and isolate therapeutically active compounds, which have been used to prepare modem medicines. In course of time, their synthetic analogues have also been prepared. In this way, ancient uses of Datura plants have led to· the isolation of hyoscine, hyoscyamine, atropine and tigloidine, Cinchona bark to quinine and quinidine, Rauvolfia serpentina to reserpine and rescinnamine, Digitalis purpurea to digitoxin and digoxin, Papaver somniferum to morphine and codeine, Ergot to crgotaminc and ergometrine, Senna to sennosides, Catharanthus roseus to vinblastine and vincristine to mention a few.
Isolation of the natural analgesic drug morphine from Papaver somniferum capsules, in 1804 is probably the first most important example of natural drugs which plants have directly contributed
to modern medicine. Isolation of other important plant-derived drugs of modern medicine rapidly followed and many useful drugs have since been discovered and introduced into modern medicine. Drugs like strychnine from Strychnos nux-vomica (1817), emetine from Cephaelis ipecacuanha ( 1817), caffeine from Camellia sinensis (1819), quinine from Cinchona species ( 1820) and colchicine from Colchicum autumnale (1820) constitute some examples of such early drugs.
The list of the plant-derived medicinal substances occurring in modern medicine is very long now. About 100 such drugs are in common use today throughout the world and about half of them are accepted as useful drugs in the industrialized countries. It is estimated that more than 35% of all prescription drugs used in the industrialized countries contain active principles that are still extracted from plants. These include drugs like atropine, colchicine, deserpidine, digoxin, L-dopa, emetine, ephedrine, ergometrine, ergotamine, hyoscine, hyoscyamine, lanatosides, lobeline, morphine, narcotine, ouabain, papain, papaverine, physostigmine, picrotoxin, pilocarpine, pseudo-ephedrine, quinidine, quinine, rescinnamine, reserpine, sennosides, sparteine, strophanthin, strychnine, theobromine, theophylline, ‘ vinblastine, vincristine, etc. Other plant-derived drugs, which are used widely include anabasine,· andrographolide, arecoline, berberine, brucine, cannabinol, cephaeline, cocaine, curcumin, glycyrrhizin, hesperidin, hydrastine, nicotine, palmitine, quercetin, rutin, santonin, vincamine, yohimbine, etc In addition to these, there are other plant-derived chemical substances that are used as drugs or necessary components of many modern medicinal preparations. These include camphor, capsaicin, eucalyptol, menthol, minor cardiac glycosides, various volatile oils, etc. These are only a few examples of a vast number of drugs that are derived from plants.
Some of these plant-derived drugs of modern medicine are listed in the following table with their plant sources and therapeutic uses. The drugs in the table are listed in alphabetical order, Which in no way reflects the degree of their medicinal or Pharmaceutical importance.