From herbal decoctions in villages to modern pharmaceutical capsules, many medicines share a common origin—nature. The discipline that studies these natural drugs, pharmacognosy, connects centuries-old traditional healing practices with today’s evidence-based medicine.
Across the world, systems like Ayurveda and Chinese medicine have long relied on medicinal plants. Meanwhile, modern allopathy continues to isolate active compounds from the same sources. UNIT 4 explores how pharmacognosy supports both traditional and modern medical systems, while also introducing the key bioactive chemicals known as secondary metabolites.
Role of Pharmacognosy in Various Systems of Medicine
Pharmacognosy in Allopathy
Modern medicine often begins with natural sources. Many important drugs were originally isolated from plants or animals.
Examples include:
- Morphine from opium
- Digitalis from foxglove
- Quinine from cinchona
Pharmacognosy helps in:
- Drug discovery
- Standardization
- Isolation of active constituents
- Quality control
Thus, even synthetic medicine relies on nature-based research.
Pharmacognosy in Ayurveda
Ayurveda uses herbs, minerals, and animal products for holistic healing.
Features
- Use of crude plant parts
- Polyherbal formulations
- Focus on balance of body energies
Pharmacognosy ensures authentication and purity of Ayurvedic raw materials.
Pharmacognosy in Unani
Unani medicine emphasizes natural remedies derived from plants and minerals.
Drugs are selected based on temperament and body constitution. Pharmacognostic evaluation prevents adulteration and ensures quality.
Pharmacognosy in Siddha
Siddha medicine uses herbal and mineral preparations.
Standardization through pharmacognosy supports safe use and consistent therapeutic effects.
Pharmacognosy in Homeopathy
Homeopathy employs highly diluted natural substances.
Pharmacognosy helps identify source materials and maintain quality standards.
Pharmacognosy in Chinese Medicine
Traditional Chinese Medicine uses herbs, roots, and fungi.
Modern research integrates pharmacognosy to isolate bioactive compounds and validate efficacy.
Introduction to Secondary Metabolites
What Are Secondary Metabolites?
Secondary metabolites are organic compounds produced by plants that are not directly involved in growth but provide defense or therapeutic benefits.
They are the primary sources of medicinal activity in crude drugs.
Classification of Secondary Metabolites
Major Groups
- Alkaloids
- Glycosides
- Flavonoids
- Tannins
- Volatile oils
- Resins
Each class has distinct chemical properties and pharmacological actions.
Alkaloids
Definition
Nitrogen-containing organic compounds with strong physiological effects.
Properties
- Bitter taste
- Basic nature
- Often toxic in high doses
Identification Tests
- Dragendorff’s test
- Mayer’s test
- Wagner’s test
These reagents produce characteristic precipitates.
Glycosides
Definition
Compounds containing sugar and non-sugar (aglycone) parts.
Properties
- Water soluble
- Hydrolyzed easily
Tests
- Borntrager’s test
- Keller–Killiani test
Commonly found in cardiac and laxative drugs.
Flavonoids
Definition
Polyphenolic compounds with antioxidant activity.
Properties
- Yellow pigments
- Free radical scavengers
Tests
- Shinoda test
- Ferric chloride test
Widely used for anti-inflammatory and cardioprotective effects.
Tannins
Definition
Astringent polyphenolic substances.
Properties
- Protein precipitation
- Antimicrobial activity
Tests
- Gelatin test
- Ferric chloride test
Useful in wound healing and diarrhea treatment.
Volatile Oils
Definition
Aromatic oils obtained by distillation.
Properties
- Characteristic smell
- Evaporate easily
Tests
- Spot test
- Steam distillation
Used as flavoring and carminative agents.
Resins
Definition
Amorphous solid or semi-solid substances.
Properties
- Insoluble in water
- Soluble in organic solvents
Tests
- Solubility tests
- Alcohol reaction
Commonly used in topical preparations.
Why This Knowledge Matters
Understanding secondary metabolites helps:
- Identify active compounds
- Standardize herbal drugs
- Ensure safety
- Discover new medicines
It forms the chemical foundation of pharmacognosy.