Medicinal plants

Categories: Economic botany and plant uses; medicine and health

The use of plants for medicinal purposes predates recorded history. Humans’ use of trial and error in their constant search for edible plants led them to discover plants containing substances that cause appetite suppression, stimulation, hallucinations, or other effects. Written records show that drugs such as opium have been in use for more than five thousand years.

From antiquity until fairly recent times, most physicians were also botanists or at least herbalists. Because modern commercial medicines are marketed in neat packages, most people do not realize that many of these drugs were first extracted from plants. Chemists have learned how to synthesize many natural products that were initially identified in a plant. However, in many cases, a plant is still the only economically feasible source of the drug. By the turn of the twenty-first century CE, an estimated 11 percent of the world's "basic and essential" drugs were derived from flowering plants alone.

Antibacterial and Anti-inflammatory Agents

Inflammation can be caused by mechanical or chemical damage, radiation, or foreign organisms. For centuries, poultices of leaves from coriander (Coriandrum sativum), thornapple (Datura stramonium), wintergreen (Gaultheria procumbens), witch hazel (Hamamelis virginiana), and willow (Salix nigra ) were used to treat localized inflammation. In the seventeenth and eighteenth centuries, cinchona bark was used as a source of quinine, which could be taken internally. In 1876 salicylic acid was obtained from the salicin produced by willow (Salix) leaves. Today, salicylic acid (also known as aspirin) and its derivatives, such as ibuprofen, are some of the most widely used anti-inflammatory drugs in the world.

Drugs Affecting the Reproductive System

A home remedy for preventing pregnancy was a tea made from the leaves of the Mexican plant zoapatle (Montanoa tomentosa). The drug zoapatanol and its derivatives were extracted from this plant to produce the first effective birth control substance. It has not been used much in human trials, however, because of potential harmful side effects. Other plant compounds that affect the reproductive system include diosgenin, extracted from Dioscorea species and used as a precursor for the progesterone used in birth control pills; gossypol from cotton (Gossypium species), which has been shown to be an effective birth control agent for men; and yohimbine, from the African tree Corynanthe yohimbe, which apparently has some effect as an aphrodisiac.

Circulatory, Analgesic, and Cancer-Fighting Drugs

Through the ages, dogbane (Apocynum cannabinum) and milkweed (Asclepias) have been prized for their effects on the circulatory system. These plants contain compounds called cardiac glycosides. Foxglove (Digitalis) has produced the most useful cardiac glycosides, digitalis and digoxin.

Opiate alkaloids—such as opium, extracted from a poppy (Papaver somniferum), and its derivatives, such as morphine—as well as cocaine, from Erythroxylum coca and Erythroxylum novogranatense var. truxillense, have long been known for their analgesic (pain-relieving) properties through their effects on the central nervous system. However, those potent chemicals can also be extremely dangerous and addictive.

The primary plant-derived anticancer agents are vincristine and vinblastine, extracted from Catheranthus roseus, maytansinoids from Maytenus serrata, ellipticine and related compounds from Ochrosia elliptica, and paclitaxel (commonly known as taxol) from the yew tree Taxus baccata.

Fighting Asthma, Gastrointestinal Disorders, and Parasites

The major antiasthma drugs come from ephedrine, extracted from the ma huang plant (Ephedra sinaica), and its structural derivatives.

Plant-derived drugs that affect the gastrointestinal tract include castor oil, senna, and aloes as laxatives, opiate alkaloids as antidiarrheals, and ipecac from Cephaelis acuminata as an emetic.

The most useful plant-derived antiparasitic agent is quinine, derived from the bark of the cincona plant (Cinchona succirubra). Quinine has been used to control malaria, a disease that has plagued humankind for centuries.

Complementary and Alternative Medicines

There are medicinal philosophies outside of conventional Western medicine that rely heavily on plants and herbal compounds to treat illness. Examples include traditional Chinese medicine (TCM) and Ayurvedic medicine, both of which are thousands of years old and tied, at least historically, to religious practice. Plants and plant roots such as ginger, turmeric, and ginseng have been used as supplements to maintain health or to treat common ailments, such as nausea.

Bioengineering

Biotechnology has provided methods by which plants can be genetically modified to produce novel pharmaceuticals. The production of specific proteins in transgenic (or, genetically modified) plants—and microorganisms such as bacteria and yeast that have been engineered to synthesize medicinal plant compounds—provides opportunities to produce large quantities of complex pharmaceuticals and other valuable products in traditional farm environments rather than in laboratories. These novel strategies open up routes for production of a broad array of natural or nature-based products, ranging from foodstuffs with enhanced nutritive value to biopharmaceuticals. Human growth hormone, active hepatitis B vaccine, and insulin are among the pharmaceutical products that have been created in this manner.

The Future

More plant-derived medicines await discovery, many from tropical rain-forest vegetation. Escalating health threats, such as antibiotic-resistant bacterial infections, and emerging infectious diseases, such as coronavirus disease 2019 (COVID-19), have spurred further research to identify potential plant-based medicinal products.

However, such research is intertwined with other global challenges. One issue is that demand for plant-derived medicines has negatively affected ecosystems, while biodiversity conservation is necessary to the survival of habitats where new medicinal plants may be located. At the same time, the widespread loss of Indigenous languages projected to occur over the twenty-first century may impair the transmission of vital ecological knowledge. Further, in the past, biopharmaceutical research has infringed on the rights of Indigenous peoples. International agreements like the 2007 United Nations Declaration on the Rights of Indigenous People (UNDRIP) seek to protect their intellectual property rights, including their knowledge and use of medicinal plants.

Scientific innovations may ease pressure on sensitive ecological areas. Along with transgenic production of medicinal-plant compounds, genomic analyses of plants and other phylogenetic approaches may help researchers better predict which plants contain medicinal compounds in future. Research also continues into new uses for known medicinal plants and their derivatives, such as aspirin in cancer treatment, and for plant waste left over from use in other industries.

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