Classification of Crude Drugs
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Direct answer
A single crude drug answers to many names: senna is a leaf to the morphologist, Cassia angustifolia to the taxonomist, an anthraquinone purgative to the pharmacist, and simply "senna" to the indexer — which is why pharmacognosy uses six parallel classification systems. The systems are alphabetical, morphological, taxonomical, chemical, pharmacological and chemotaxonomic, and each answers a different practical question: how to find a drug in a book, how to identify it, how to relate it to botany, or how to predict its action. Examiners most often demand the morphological system's split into organized and unorganized drugs.
What you must remember
- Alphabetic system: arrangement A to Z by Latin or English name; used by the IP, BP and USP for monographs — ideal for quick location, tells nothing about the drug.
- Morphological system divides drugs by plant part: leaves, barks, woods, roots, rhizomes, flowers, fruits, seeds, hairs and fibres.
- Organized drugs possess cellular tissue (senna leaf, cinnamon bark, clove flower, ginger rhizome); unorganized drugs are products — latex, juices, extracts, gums, resins, fixed oils, waxes — obtained by incision or extraction, lacking cellular structure.
- Unorganized examples: opium (dried latex), aloe (dried juice), acacia (gum), asafoetida (oleo-gum-resin), castor oil (fixed oil), beeswax.
- Taxonomical system groups by family: Solanaceae yields belladonna, datura and hyoscyamus; Apocynaceae yields rauwolfia and kurchi.
- Chemical system groups by constituent: alkaloid drugs (opium, cinchona, rauwolfia), glycoside drugs (digitalis, senna), volatile-oil drugs (clove, mentha).
- Pharmacological system groups by action: purgatives (senna, cascara, castor oil), bitters (gentian, quassia), carminatives (ginger, fennel).
- Chemotaxonomic system uses chemical constituents as taxonomic markers within a family, for example tropane alkaloids tracking through Solanaceae.
One drug carried through all six systems
Take ginger and classify it every way to see what each system buys you. Alphabetically it sits under Z or G depending on the index chosen — trivial, but that is how the pharmacopoeia is physically arranged. Morphologically it is an organized drug, the dried rhizome of Zingiber officinale, and its section shows oleoresin-filled cells and scattered vascular bundles. Taxonomically it belongs to Zingiberaceae alongside turmeric and cardamom, which share secretory oil cells. Chemically it is an oleoresin drug, yielding the pungent gingerols and shogaols plus a volatile oil rich in zingiberene. Pharmacologically it is a carminative, aromatic and flavouring agent with antiemetic use. Chemotaxonomically, the consistent occurrence of volatile oils and oleoresins across Zingiberaceae lets you predict that a new plant of this family probably smells and probably contains terpenoids.
Now do the reverse in an exam: if asked to place aloe, do not write "organized" — aloe is dried juice, unorganized. If asked which system the IP uses, answer alphabetical. If asked which system suits a prescription-writing doctor, answer pharmacological, because clinicians think in therapeutic classes, not in plant parts.
The slip that costs the most marks
The organized/unorganized boundary is where scripts fail. Students memorise the words but invert the logic: organized does not mean "neatly arranged" — it means the drug still consists of cells, the actual plant part itself. Unorganized drugs are derivatives, things that oozed, exuded or were extracted: a gum, a latex, a juice, a resin, an oil. The quickest self-test is microscopy — senna under the lens shows leaf architecture; acacia shows none, only amorphous gum fragments.
A second trap: presenting chemical classification as the "best" system. It is attractive but unstable, because a plant's constituents vary with season, locality and chemical race — cinchona barks of different quinine content would drift between groups. Examiners reward the caveat, not the enthusiasm.
Frequently asked questions
Which classification system do the pharmacopoeias use?
The alphabetical system — IP, BP and USP monographs are arranged A to Z by drug name for rapid location, at the cost of grouping unrelated drugs together.
Differentiate organized and unorganized crude drugs with examples.
Organized drugs retain cellular structure and are plant parts (senna leaf, cinnamon bark); unorganized drugs are products lacking cellular structure, obtained by incision or extraction (opium latex, acacia gum, aloe juice, beeswax).
Give the taxonomical classification of two Solanaceae drugs.
Belladonna (Atropa belladonna) and datura (Datura stramonium or innoxia), both yielding tropane alkaloids — hyoscyamine, atropine and hyoscine.
What is chemotaxonomic classification?
Grouping plants by chemical constituents shared through evolutionary relationship, such as tropane alkaloids as markers of the Solanaceae family.
Why is chemical classification called imperfect?
Because constituent content varies with plant part, season, soil and chemical variety, so the same drug can shift between chemical groups, unlike morphology which is fixed.