2. CLASSIFICATION OF CRUDE DRUGS

CLASSIFICATION OF DRUGS: A TEACHER’S COMPREHENSIVE GUIDE

Welcome, future pharmacognosists and pharmaceutical scientists!

A crude drug can be defined as a naturally occurring substance originating from plants, animals, minerals, or microbes that have therapeutic qualities in their raw or unprocessed form. Before the introduction of contemporary medicines, these compounds were historically utilised for medical reasons in numerous cultures and civilisations. They were used exactly as they occur naturally with the exception of drying and size reduction.

The significant natural sources of drugs include higher plants, microbes, animals, and marine organisms. Other valuable products are extracted from organic or inorganic minerals. To carry out the study of individual drugs, some particular sequence of arrangement, known as the system of drugs classification, should be followed.

As a pharmacognosy educator with years of experience teaching natural products, I have observed that students often find drug classification confusing. Let me tell you: Understanding drug classification systems is essential for the systematic study, identification, and standardization of crude drugs.

In this comprehensive guide, I will walk you through the six major systems of drug classification—Alphabetical, Taxonomical, Morphological, Pharmacological, Chemical, and Chemo-taxonomical classification. By the end of this article, you will have a thorough understanding of each system, along with their merits and demerits. Let us begin!

Dpharmguru’s exam insights:

Classification of drugs is frequently tested in pharmacognosy exams. Remember: There are six systems of drug classification—Alphabetical, Taxonomical, Morphological, Pharmacological, Chemical, and Chemo-taxonomical. Each system has its own merits and demerits. The alphabetical system is the easiest and most accessible. The pharmacological system is useful for rational prescribing. The chemical system is preferred for phytochemical studies. These are classic exam questions!

2.1. ALPHABETICAL CLASSIFICATION

In the alphabetical classification system, the arrangement of crude drugs is done alphabetically by their Latin and English names.

Pharmacopoeias and reference books using this system:

• Indian Pharmacopoeia
• British Pharmacopoeia
• British Herbal Pharmacopoeia
• United States Pharmacopoeia and National Formulary
• British Pharmaceutical Codex
• European Pharmacopoeia (Latin titles)

Note:

• United States Pharmacopoeia (USP) and British Pharmaceutical Codex (BPC) arrange drugs in alphabetical order of their English names
• European Pharmacopoeia arranges drugs in alphabetical order of their Latin names

Examples of drugs arranged by alphabetical classification:

Acacia, Benzoin, Cinchona, Dill, Ergot, Fennel, Gentian, Hyoscyamus, Ipecacuanha, Jalap, Kurchi, Liquorice, Myrrh, Nux-vomica, Opium, Podophyllum, Quassia, Rauwolfia, Senna, Uncaria gambier, Vasaka, Wool fat, Yellow bees-wax, Zedoary.

Merits

• It is the easiest and quickly accessible system of classification
• It does not repeat entries and thus does not create confusion
• It facilitates location, tracking, and drug addition

Demerits

• The system fails to explain the scientific nature of the drug (i.e., whether it is organised or unorganised)
• The system lacks to differentiate between the various sources (i.e., plant, animal, and mineral) of the drug origin

2.2. TAXONOMICAL/BIOLOGICAL CLASSIFICATION

Different plants show different characters related to its morphology, microscopy, chemical nature, embryological status, serological, and genetic information. In taxonomical or biological classification system, the crude drugs are classified by kingdom, division, class, sub-class, order, family, tribe, genus, species, and sub-species.

Taxonomical Hierarchy

Key Terms

• Kingdom: Highest taxonomic level; comprises all plants (Plantae)
• Division: Comparable to an animal’s phylum; e.g., Magnoliophyta (flowering plants), Coniferophyta (cone-bearing plants)
• Class: Angiospermae (flowering plants) and Gymnospermae (non-flowering plants)
• Sub-class: Dicotyledonae (two embryonic leaves) and Monocotyledonae (one embryonic leaf)
• Order: Names end with suffix -ales
• Family: Names end with suffix -aceae
• Tribe: Names end with suffix -eae
• Genus: Most acquainted part of the plant name (e.g., Papaver, Aquilegia)
• Species: Specifies an individual plant; name comes after genus in small letters
• Sub-Species: Plants with slightly different traits

Merits of Biological Classification

• It explains the evolutionary developments
• It organises and categorises organisms based on evolutionary relationships
• It offers standardised names for species

Demerits of Biological Classification

• It fails to recognise the organised and unorganised forms of crude drug
• Initially interesting, but many drugs are not entire plants and represent processed plant parts
• Chemical nature of active constituents and therapeutic significance is not included

2.3. MORPHOLOGICAL CLASSIFICATION

In morphological classification system, the arrangement of crude drugs is done according to the plant parts in use—roots, stems, leaves, barks, flowers, fruits, seeds, etc.

Drugs are classified into:

• Organised Drugs: Obtained directly from plant parts, containing cellular tissues (rhizomes, barks, leaves, fruits, entire plants, hair, and fibres)
• Unorganised Drugs: Prepared from plants through intermediate physical processes (drying, incision, or solvent extraction); do not contain cellular plant tissues

Organised Drugs

Unorganised Drugs

Merits of Morphological Classification

• It facilitates identification and detection of adulteration
• It aids in practical study of crude drugs with known chemical nature

Demerits of Morphological Classification

• It repeats drugs or plants thus creating confusion
• The chemical constituents have no correlation with the therapeutic actions

2.4. PHARMACOLOGICAL/THERAPEUTICAL CLASSIFICATION

In pharmacological or therapeutical classification system, the crude drugs are classified based on the pharmacological action of their active constituent or their therapeutic uses. If drugs exhibit similar pharmacological action, they are put together irrespective of their morphology, taxonomy, or chemical relationship.

Examples of Pharmacological Classification

Merits of Pharmacological Classification

• It aids in recommending substitutes of an unavailable drug
• It facilitates rational prescribing and drug selection

Demerit of Pharmacological Classification

• It classifies drugs with different actions into many groups, creating confusion
• Example: Cinchona is an anti-malarial (due to quinine) but also affects the heart (due to quinidine)

2.5. CHEMICAL CLASSIFICATION

In chemical classification system, the crude drugs are classified as per the chemical nature of their significant constituent. This classification system is preferred because the pharmacological and therapeutic activity of crude drugs depends on the nature of chemical constituents present.

Examples of Chemical Classification

Merits of Chemical Classification

• Phytochemical studies are well performed through this system
• Facilitates drug selection and rational prescribing

Demerit of Chemical Classification

• Confusion occurs when a drug contains many compounds belonging to different groups

2.6. CHEMOTAXONOMICAL CLASSIFICATION

The vastness of phytochemical screening proved that a relationship between plant constituents and their taxonomy does exist. Chemotaxonomy relates the position of plants and uses chemical knowledge to comprehend biological evolution and relationships.

Chemotaxonomy is also described as chemical plant taxonomy, chemosystematics, and plant chemistry. It focuses on secondary metabolites (alkaloids, glycosides, flavonoids, etc.) of pharmaceutical relevance.

Examples:

• Presence of essential oils helps in the identification of Apiaceae and Lamiaceae families
• Presence of milky latex helps in distinguishing Apocynaceae and Asclepiadaceae families

Analytical techniques used: Chromatography, Electrophoresis, X-ray crystallography

Merits of Chemotaxonomical Classification

• It is recent and provides better understanding of the relationship between chemical constituents, their biosynthesis, and action
• It provides a systematic approach to classify organisms on the basis of chemical characteristics

Demerits of Chemotaxonomical Classification

• It is a time-consuming process as chemical identification is complex
• Limited applicability to non-chemically diverse taxa

Dpharmguru’s exam insights:

Chemotaxonomy is a modern and frequently tested topic. Remember: Chemotaxonomy relates chemical constituents to plant taxonomy. It focuses on secondary metabolites like alkaloids, glycosides, and flavonoids. Examples: Essential oils identify Apiaceae and Lamiaceae families. Milky latex distinguishes Apocynaceae and Asclepiadaceae. These are classic exam questions!

COMPARISON: SIX SYSTEMS OF DRUG CLASSIFICATION

FREQUENTLY ASKED QUESTIONS (FAQs)

1. What are the six systems of drug classification?

The six systems of drug classification are: Alphabetical, Taxonomical, Morphological, Pharmacological, Chemical, and Chemo-taxonomical classification.

2. Which classification system is the easiest?

The Alphabetical classification system is the easiest and most accessible because drugs are arranged in alphabetical order and can be located quickly.

3. What is the difference between organised and unorganised drugs?

Organised drugs are obtained directly from plant parts and contain cellular tissues (e.g., leaves, roots, barks). Unorganised drugs are prepared through physical processes like drying or extraction and do not contain cellular tissues (e.g., gums, resins, oils).

4. What is chemotaxonomy?

Chemotaxonomy is the classification of plants based on their chemical characteristics. It focuses on secondary metabolites (alkaloids, glycosides, flavonoids) to understand evolutionary relationships.

5. Which pharmacopoeia uses Latin titles for alphabetical classification?

The European Pharmacopoeia arranges drugs in alphabetical order of their Latin names.

6. What is the disadvantage of pharmacological classification?

The main disadvantage is that drugs with multiple actions are classified into many groups, creating confusion. For example, Cinchona is an anti-malarial (due to quinine) but also affects the heart (due to quinidine).

SUMMARY

Classification of crude drugs is essential for systematic study, identification, and standardization. This guide covered the six major classification systems:

• Alphabetical Classification: Arranged by Latin/English names—easiest but lacks scientific basis
• Taxonomical Classification: Based on evolutionary relationships—explains evolution but no chemical/therapeutic info
• Morphological Classification: Based on plant parts—helps identify adulteration but repeats drugs
• Pharmacological Classification: Based on therapeutic action—useful for prescribing but confusing for multi-action drugs
• Chemical Classification: Based on chemical nature of constituents—useful for phytochemical studies but confusing for multi-constituent drugs
• Chemo-taxonomical Classification: Based on chemical characteristics + taxonomy—modern but time-consuming

As I always tell my students: “Understanding drug classification systems is the first step toward mastering pharmacognosy. Each system has its strengths and weaknesses—choose the right system based on your purpose of study.”

REFERENCES AND FURTHER READING

• Pharmacy Council of India (PCI). (2022). Pharmacognosy Syllabus. New Delhi: PCI.
• Tyler, V. E., Brady, L. R., & Robbers, J. E. (2020). Pharmacognosy and Pharmacobiotechnology (9th ed.). Wolters Kluwer.
• Trease, G. E., & Evans, W. C. (2019). Trease and Evans’ Pharmacognosy (16th ed.). Elsevier.
• Kokate, C. K., Purohit, A. P., & Gokhale, S. B. (2020). Pharmacognosy (50th ed.). Nirali Prakashan.
• Indian Pharmacopoeia Commission. (2018). Indian Pharmacopoeia (8th ed.). Ghaziabad: IPC.

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult qualified healthcare professionals for medical concerns. Pharmaceutical regulations and guidelines may vary by region—always refer to your local regulatory authorities for specific requirements.

written by:
Dr. N. Sujith Kumar

Dr. N. Sujith Kumar is a pharmacy educator, Pharm.D graduate, and academic content creator from Jawaharlal Nehru Technological University Kakinada (JNTUK), where he completed his Doctor of Pharmacy (Pharm.D) degree between 2015 and 2021. He has more than 7 years of experience creating pharmacy educational content, writing study materials, and reviewing academic articles for pharmacy students. He has also contributed guest articles to pharmacy education platforms, including PharmD Guru. At D.PharmGuru, his work focuses on simplifying complex Diploma in Pharmacy (D.Pharmacy) subjects into easy-to-understand notes, practical explanations, and exam-oriented educational resources for students across India. His areas of focus include Human Anatomy and Physiology, Pharmaceutics, Pharmacology, Pharmaceutical Chemistry, Hospital and Clinical Pharmacy, and other core D.Pharmacy subjects.

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