Origin, Nature, and Sources of Medicine

The field of medicine revolves around drugs—substances used to treat, cure, diagnose, or prevent disease. The very word "drug" traces its roots to the French word "drogue," meaning "dry herb," highlighting the historical reliance on plant-based remedies.

A drug is broadly defined as any substance, natural or synthetic, used to achieve a beneficial pharmacological effect. This includes applications beyond treating illness, such as contraception, managing non-disease conditions, or maintaining optimum health.

1. 🔬 The Nature of Drugs: Properties That Matter

The activity of a drug in the body—how it is absorbed, distributed, and interacts with targets—depends critically on its physical and chemical characteristics.

A. Physical Properties

This simply refers to the state of the drug at room temperature:

Solid: Most common; e.g., Aspirin, Paracetamol.
Liquid: Less common; e.g., Nicotine, Ethanol.
Gas: Used mainly as anesthetics; e.g., Nitrous Oxide.

B. Chemical Properties

Drugs are categorized based on their chemical structure, though the majority are organic (carbon-based).

Organic Drugs: Contain carbon atoms; e.g., Penicillin, Cocaine. They are further classified by their behavior in solution:

Weakly Acidic: e.g., Aspirin, Penicillin.
Weakly Basic: e.g., Morphine, Chloroquine.
Non-Electrolytes: Neutral molecules; e.g., Alcohol, Diethyl-ether.

Inorganic Drugs: Do not have a carbon basis; e.g., Ferrous Sulfate (Iron supplement), Magnesium Hydroxide (Antacid).

C. Drug Size (Molecular Weight)

The size of a drug molecule is measured in Daltons ( $\text{D}$ ) or grams/mole. Most drugs fall within the range of 100 to $1000 \text{ D}$ .

Molecules less than $100 \text{ D}$ (e.g., Lithium at $\approx 7 \text{ D}$ ) may lack the unique properties (like shape and configuration) needed for highly specific binding.
Molecules greater than $1000 \text{ D}$ (e.g., Heparin at $\approx 10-20 \text{ kD}$ ) cannot readily diffuse across cell membranes and require special transport mechanisms or are administered parenterally.

D. Drug Shape and Chirality

A drug's shape must be complementary to its binding site (e.g., a receptor) much like a lock and key . This specific fit is what promotes the desired action.

Many drugs exhibit chirality (existing as non-superimposable mirror images, or enantiomers), where one form (e.g., R- or S-isomer) is often much more active than the other.

2. 🌍 Versatile Origins: Where Do Drugs Come From?

The origin of drugs is diverse, spanning natural sources, laboratory synthesis, and advanced technology.

Source	Description	Examples of Drugs/Substances
A. Plant Source	The most abundant historical source; obtained from leaves, flowers, roots, etc.	Digitalis (from leaf), Opium (from fruit), Rauwolfia (from root), Cinchona (Quinine, from bark)
B. Animal Source	Derived from organs, fluids, or tissues of animals.	Insulin (historically from cow/pig pancreas), Pepsin (from stomach), Cod Liver Oil, Gelatin (from bone)
C. Minerals	Inorganic compounds obtained from the earth's crust.	$\text{FeSO}_4$ (Iron, for anemia), $\text{NaHCO}_3$ (Sodium Bicarbonate, antacid), $\text{MgSO}_4$ (Magnesium Sulfate, purgative)
D. Microbial Source	Derived from microorganisms like bacteria and fungi, primarily for antibiotics.	Penicillin (from Penicillium notatum), Streptomycin (from Streptomyces griseus)
E. Synthetic Source	Drugs prepared entirely in a laboratory and not found naturally.	Antihistamines, Antipyretics (fever reducers), Ampicillin (semi-synthetic penicillin)
F. Biotechnological Source	Prepared using recombinant $\text{DNA}$ technology, combining biology and technology.	Human Insulin (prepared by altering the $\text{DNA}$ of E. coli bacteria), Growth Hormones