Introduction to Natural Products and Evidence-Based Herbal Medicines

Historical Role of Plants in Medicine and Traditional Systems

Plants maintain a universal role in the treatment of diseases across all major medical systems globally. Information regarding these treatments has historically been transferred through two primary methods:

  • Oral Transfer: Knowledge passed from generation to generation verbally. This is common in tropical Africa, North and South America, and Pacific countries.

  • Written Transfer: Documentation in historical records, such as the Egyptian Papyrus Ebers (c.1600 BCc. 1600\,BC).

Major historic systems of medicine centered around specific regions include:

  • Western Medicine roots: Found in Mesopotamia and Egypt.

  • Unani-Islamic and Ayurvedic (Hindu) systems: Centered in Western Asia and the Indian subcontinent.

  • Oriental systems: Including China, Japan, and Tibet.

The Ebers Papyrus

The Ebers Papyrus was discovered in Egypt in the 1870s1870s and was published in Leipzig in 18751875 by Georg Ebers (1837−18981837-1898). It is a significant historical document containing prescriptions written in hieroglyphics for over seven hundred remedies.

An example of a remedy found in the papyrus is an asthma treatment. It was prepared as a mixture of herbs heated on a brick, allowing the sufferer to inhale the resulting fumes.

Defining Pharmacognosy

The term "Pharmacognosy" is derived from two Greek words:

  • Pharmakon: Means a drug or medicine.

  • Gignosco: Means to acquire knowledge of.

Pharmacognosy is defined as an applied science that deals with the biological, biochemical, and economic features of natural crude drugs and their active constituents. It is a unified discipline that integrates several fields, including:

  • Botany

  • Chemistry

  • Horticulture

  • Enzymology

  • Genetics

  • Quality Control

  • Pharmacology

  • Commerce

While Pharmacognosy utilizes the methods of medicinal chemistry and pharmacology, it is not identical to them. Notably, it does not include the study of synthetic drugs, though natural drug constituents that have been prepared synthetically are considered a definite part of the field. Examples of such substances include:

  • Ephedrine

  • Vanillin

  • Caffeine

  • Codeine

  • Menthol

  • Penicillin

Scope and Relationships of Pharmacognosy

Pharmacognosy is most closely related to botany and plant chemistry, which originate scientific studies on medicinal plants.

  • Botanical Aspect: It is concerned with the description and identification of drugs in both their whole and powder states. It also covers their history, commerce, collection, preparation, and storage, which are essential for pharmacopoeial identification and quality control.

  • Biodynamic Compounds: While often associated with plants, Pharmacognosy also investigates biodynamic compounds in animals (e.g., thyroid gland and its extracted hormone thyroxin), marine organisms, fungi, and micro-organisms.

Examples of crude drugs and their constituents include:

  • Digitalis leaf: Contains glycosides such as digitoxin.

  • Rauwolfia root: Contains alkaloids such as reserpine.

  • Thyroid gland: Source of the hormone thyroxin.

Pharmacognosists contribute to the screening of large numbers of plants for pharmacological values, such as hypoglycemic properties, to discover new substances of medicinal value.

Professional Roles and Related Disciplines

Pharmacognosists perform several key functions:

  • Isolation and characterization of active constituents.

  • Characterization of the pharmacology of crude extracts and active constituents.

  • Evaluation of the quality of natural medicines.

  • Interdisciplinary collaboration with ethnobotany and ethnopharmacology.

Definitions of Related Fields

  • Ethnopharmacology: The scientific study correlating ethnic groups, their health, and how it relates to their physical habits and methodology in creating and using medicines.

  • Ethnobotany: The study of the relationship between people and plants. This field includes studying plants as medicines, alternative healing methods, wild foods, agricultural crops, modes of transportation, clothing, and roles in religious ceremonies.

Crude Drugs

Crude drugs are vegetable or animal drugs consisting of natural substances that have undergone only the processes of collection and drying. The term "natural substances" refers to materials found in nature that have not had changes made to their molecular structure. This includes:

  • Whole plants or plant organs (leaves, flowers, seeds, barks).

  • Vegetable saps, extracts, and secretions.

  • Whole animals, glands, animal organs, extracts, or secretions.

A product is no longer considered a crude drug if it has been advanced in value or improved in condition by processes like grinding, chipping, crushing, distilling, evaporating, extracting, or artificial mixing, beyond what is essential for proper packing and prevention of decay during manufacture.

Sources and Examples of Crude Drugs

  • Plant sources: Senna, Digitalis, Datura, Cascara, Cinchona, Clove, Opium.

  • Animal sources: Cochineal, cantharidin, honey, cod liver oil, musk, thyroxin.

  • Marine sources: Sponges, red algae, agar.

  • Mineral sources: Talc, kaolin, kieselguhr.

Natural Products and Their Uses

A natural product is a substance obtained from a natural source. This category includes:

  1. Crude drugs: e.g., Senna, Cascara, Cinchona.

  2. Galenical preparations: e.g., Extracts and tinctures.

  3. Pure compounds: e.g., Morphine, atropine, digoxin.

  4. Semi-synthetic products: e.g., Etoposide, teniposide, hyoscine butyl bromide.

General and Industrial Uses

  • Medicine: Drugs for treating a wide range of diseases (antibiotics, hormones, morphine).

  • Pharmaceutical Aids: Used as suspending and emulsifying agents, suppository bases, binders, excipients, sweetening, and coloring agents.

  • Cosmetics: Used as flavoring and coloring agents.

  • Microbiology/Biotechnology: Used in culture media for the propagation of microorganisms.

  • Food and Perfumery: Used as dusting powders, indicators, and fragrances.

Classification of Medicinal Plants

  • Alphabetical: Uses Latin or Vernacular (common) names. Simple for quick reference but provides no indication of interrelationships.

  • Taxonomic: Based on botanical classification (Classes, orders, families, genera, species).

  • Morphological:

    • Organized Drugs: Divided into groups by plant part (leaves, flowers, fruits, wood, barks, rhizomes, etc.).

    • Unorganized Drugs: Includes dried lattices, extracts, gums, resins, oils, fats, and waxes.

  • Pharmacological or Therapeutic: Grouped according to the pharmacological action of the most important constituents or therapeutic uses (e.g., cardiotonic drugs).

  • Chemical or Biogenetic: Based on important constituents (alkaloids, glycosides, volatile oils) or biosynthetic pathways. Popular in phytochemically-biased teaching.

Pharmacopoeias and Monographs

A Pharmacopoeia is a book recognized by the government as a legal authority for the standardization of drugs. It ensures traditional herbs meet legal requirements for quality, efficacy, and safety. Examples include the British Herbal Pharmacopoeia (19961996), United States Herbal Pharmacopoeia, and Chinese Herbal Pharmacopoeia.

Definitions of Drug Status

  • Official Drug: Listed and described as a definite therapeutic agent in the pharmacopoeia.

  • Unofficial Drug: Not recognized in the pharmacopoeia but still used as a therapeutic agent.

The Monograph

A monograph is the descriptive material pertaining to a drug in the pharmacopoeia. It generally includes:

  • Names: English, Arabic, Latin, French.

  • Definition and descriptions.

  • Specific conditions for collection or market preparation.

  • Identity tests and tests for adulterants.

  • Method of assay and dose requirements.

  • Special storage requirements and biological/natural origin.

Biological Origin and Nomenclature

Knowing the biological origin (Botanical for plants, Zoological for animals) allows for the precise identification of material. Potency can vary by species; for instance, Strophanthus seeds may be active or poisonous depending on the species collected. Authentic or genuine samples are used for comparison to ensure consistent potency.

Binomial System

Founded by Swedish botanist Carolus Linnaeus (1707−17781707-1778), this system uses two names followed by the author's name:

  • First Name: Genus (starts with a capital letter).

  • Second Name: Species.

  • Author Examples: Artemisia cina Berg., Caryophyllos aromaticus L.

  • Derivative Names: Species can be named after people, such as Cinchona Ledergiana, named after Charles Ledger who brought seeds from Brazil in 18651865.

Species Naming Conventions

  • Striking Characteristics: Cassia acutifolia (sharp pointed leaflets), Conium maculatum (spotted), Glycyrrhiza glabra (smooth), Atropa belladonna (beautiful lady), Hyoscyamus muticus (short).

  • Characteristic Color: Piper nigrum (black), Digitalis purpurea (purple), Digitalis lutea (yellow), Brassica alba (white).

  • Aroma: Myristica fragrans (nice aroma), Caryophyllus aromaticus.

  • Geographical Source: Cinnamoum zeylanicum (Ceylon), Hydrastis Canadensis (Canada), Tamarindus indica (India).

  • Pharmacological Activity: Papaver sominferum (inducing sleep), Lytta vesicatoriam (causing blistering), Strychnos nux-vomica (causing vomiting), Ipomoea purge (purgative).

  • General Meaning: Allium sativum (cultivated), Riticum vulgare (wild), Linum usitatissimum (most useful).

  • Generic Meanings: Atropa (fate who cuts the thread of life), Glycyrrhiza (sweet root), Linum (thread).

Production: Collection, Drying, and Storage

Collection Factors

  1. Seasonal Variation: Active constituents vary throughout the year. Rhubarb is collected in summer because it contains anthranol in winter which converts to anthraquinones in summer. Colchicum corm and Hyoscyamous muticus are collected for alkaloids in spring and summer, respectively.

  2. Time of Day: Digitalis is collected in the afternoon. Solanaceous leaves are collected in the morning. Salix is collected at night.

  3. Maturity and Age: Cloves and Santonica are collected as buds. Solanaceous leaves are collected at the flowering stage. Pyrethrum flowers are collected when fully expanded.

  4. Environment: Flowers and unorganized drugs are collected in dry weather. Barks are collected in spring when easily separated. Underground organs are collected once aerial parts die down.

Drying Methods and Intent

Drying decreases size and weight for transport, facilitates powdering, and prevents degradation or microbial growth.

  • Enzyme Action: Drying quickly is desirable for Digitalis to stop undesirable enzymes. Slow drying is desirable for Vanilla pods.

  • Open Air: Drying in the sun or under sheds (e.g., clove, cinnamon).

  • Artificial Oven: Faster than air; controlled temperatures (20−40∘C20-40^{\circ}C for leaves/flowers; 40−65∘C40-65^{\circ}C for barks/roots).

  • Vacuum Drying: Rapid drying at low temperatures.

  • Lyophilization: Used for enzymes, proteins, biological fluids, and royal jelly.

Storage

Drugs are susceptible to physicochemical deterioration (light, moisture, temperature, oxygen) and biological deterioration (fungi, bacteria, insects, mites). Long storage is discouraged. Drugs should be stored in sealed containers in cool, dark places.