Pharmacognosy- Classification of Drugs


There are thousands of plant species used as medicine. The drugs used in Indian traditional systems of medicines are 90% based on plant sources. These drugs are considered to be safe, cost effective and having minimal side effects.  To study the individual drug, from variety of drugs sources and their uses, one must use a systemic sequence of arrangement. Classification of drugs clear the confusion of due to diversity of drugs. In this article we will see the various classification of drugs which helps to simplify understanding of drugs.

Classification of drugs

A method used for drug classification must possess following properties,

  • Simple
  • Easy to use
  • Free from confusion and ambiguities
Classification of Crude Drugs (Pharmacognosy)
Classification of Crude Drugs (Pharmacognosy)

Drugs are classified in different ways; each classification has its own advantages and disadvantages. Drugs are classified in following different ways;

  • Alphabetical classification
  • Morphological classification
  • Taxonomical classification
  • Chemical classification
  • Pharmacological classification
  • Chemo-taxonomical classification
  • Sero-taxonomical classification

Alphabetical classification

It is the simple way drug classification. In this drug are arranged according to alphabetical order of their Latin and English names (common names) or local names (vernacular names). Some important pharmacopeia’s, dictionaries and reference books use this classification.

  • Indian pharmacopeia
  • British pharmacopeia
  • British herbal pharmacopeia
  • United state pharmacopeia
  • British pharmaceutical codex
  • European pharmacopeia

In European pharmacopeia drugs are arranged according to their Latin terms and in United state pharmacopeia and British pharmaceutical codex drugs are arranged to their English names.


  • It is easy and fast to use.
  • There is no repetition of drugs which avoid confusion.
  • In this classification location, tracing and addition of new drug entries is easy.


  • There is no relationship between previous and successive drug entries.

Morphological classification

In this system drugs are arranged according to morphological or external characters of the plants or animal parts. The drugs which are direct parts of the plant or animal and contain cellular tissue are called as organised drugs. For example, leaves, bark, hair, etc. The drugs which are obtained by some intermediate physical process like incision, drying or extraction and do not contain any cellular tissues are called unorganised drugs. For example, aloe juice, gelatin, honey, beeswax, etc.


  • This method useful when chemical nature of drug is not clearly known.
  • It gives clear idea about the source of drugs.
  • This classification helpful to identify and detect adulteration.


  • There is no relation with chemical constituents and therapeutic actions.
  • Repetition of drugs occurs.

Taxonomical classification

In this classification drugs are classified according to kingdom, subkingdom, division, class, order, family, genus and species. Taxonomical classification is a botanical and zoological classification of plants and animals respectively.


Class: Angiospermae

Sub class: Dicotyledonae

Order: Rutales

Family: Rutaceae

Drug: Orange peel and lemon peel


  • This system helps to study evolutionary developments of crude drugs.
  • Taxonomical information gives details about species and varieties of organisms.


  • This classification does not provide any information related to chemical nature.
  • This system does not provide any correlation between chemical constituents and biological activity of drugs.
  • This also does not provide any information about organised or unorganised nature of crude drugs.

Chemical classification

In this crude drug are classified according to the chemical constituent of it. For example,

Chemical constituentExamples
AlkaloidsVinca, belladonna, opium, tea
GlycosidesSenna, digitalis, aloe, wild cherry
LipidsCastor oil, peanut oil
Volatile oilsClove, coriander, fennel
TannisCatechu, galls
VitaminsYeast, cod liver oil, shark liver oil
Resin and resin combinationsBenzoin, guggul, shellac
Carbohydrates and derived productsAgar, honey, starch, acacia


  • It is important for phytochemical studies.
  • Due to knowledge of chemical constituents, it is easy to study the use of drug.


  • This method does not provide any idea about the source of drug and whether the drug is organized or unorganized.
  • Some drugs contain two or more chemical constituents, then it is difficult to classify them according to this method.

Pharmacological classification

In this classification crude drugs are classified according to pharmacological action of their important chemical constituent. For example,

Pharmacological actionExample
AnthelminticsQuassia, male fern
Anti-amoebicKurchi, ipecacuanha
AntispasmodicDatura, belladonna
AnticancerVinca, podophyllum
BittersNux vomica, cinchona
CarminativesFennel, dill, clove
CardiotonicDigitalis, squill
CNS stimulantOpium, tea
PurgativeAloe, senna
ExpectorantVasaka, nutmeg, liquorice
AstringentMyrobalan, black catechu
Immunomodulatory agentsAshwagandha, tulsi, ginseng


  • This system helps to suggest substitutes of drugs if particular drug is not available at particular time and place.


  • It is difficult to classify some drugs having two or more different pharmacological actions.

Chemo-taxonomical classification

The phytochemical screening of several drugs suggests that there is close relationship between chemical constituents of plants and its taxonomical status. In this method of classification equal importance is given to their taxonomy and chemical constituents. For example, berberine alkaloid in berberis and argemone, rutine in rutaceae.


  • It gives more scope for understanding relationships between chemical constituents, their biosynthesis and possible action.


  • This system fails to understand therapeutic nature of crude drugs.

Sero-taxonomical classification

This method is the application of serology (study of antigen and antibody reactions). The use serology to solve taxonomic problems known as Sero-taxonomy.


  • This technique helps in the comparison of single proteins from different plants.


  • This method of classification does not provide any information about organised or unorganised nature of crude drugs.


Various crude drugs are obtained from natural sources are used in the treatment of diseases. For their adequate study it is necessary to arrange them in scientific and systematic manner. Classification of natural drugs help us to arrange and study them systematically. There are various methods of drug classification. Each one of them have some advantages and some disadvantages as we discussed above.

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