Drug types

Types

There are broadly two types of drugs. Biologics (aka. Large Molecules) and Small Molecules.

Drug molecule comparison. Biologic left, Small molecule right

Comparison

General characteristics of biologic and small molecule drugs

		Biologics	Small Molecules
Design and Manufacture	Design	They have large complex structures with intricate folds held together by weaker non-covalent bonds. Can have 1000’s or even 10,000s of atoms.	They have small simpler structures with mostly fewer and stronger covalent bonds. Typically 20-100 atoms.
	Manufacture	Made by a complex bioprocess using living organisms.	Made by simpler chemical synthesis.
Effectiveness	Efficacy	Revolutionary, especially for chronic hard-to-treat diseases (e.g. cancer and autoimmune diseases).	Medications exist for both acute and chronic diseases.
	Side effects	Lower toxicity and side effects. Their bespoke complex structure results in high selectivity, binding mostly to just what they're intended to.	Greater toxicity and side effects. Their smaller and simpler structure results in lower selectivity, interacting and binding with more unintentional off-target sites.
	Storage	Their large and delicate structure make them sensitive to physical conditions (temperature, shear stress, light etc.).	Their small structure, mostly composed of strong covalent bonds, makes them more robust and less sensitive to physical conditions.
	Administration	Injected, therefore less patient friendly. Their complex and fragile folded structure cant survive the digestive tract, and their large structure cant be absorbed through it either.	Swallowed/Inhaled/Absorbed through the skin, therefore more patient friendly. Their small and stable structure is often able to survive the digestive tract, and they can be absorbed through it too.
Business	Market size	Minority of drugs. Relatively novel but are becoming increasingly common.	Majority of drugs currently on the market.
	Cost	Extremely expensive. Complex to design, manufacture, and administer. Furthermore, on patent expiry, they are still challenging manufacture, with biosimilars only reducing cost by tens of percent.	Cheap. Simpler to design, manufacture and administer. Furthermore, after patent expiry, they are easier to copy, with generics often reducing cost by an order of magnitude.