How do medicines work?

Drugs Bind to Their Receptors

Many drugs exert their physiological effects by binding to specific sites, called receptors , on the
surface of certain cells  . A drug binds to a receptor using the same kinds of bonding
interactions—van der Waals interactions, dipole–dipole interactions, hydrogen bonding—that
molecules use to bind to each other.
The most important factor in the interaction between a drug and its receptor is a snug fit.
Therefore, drugs with similar shapes and properties, which causes them to bind to the same
receptor, have similar physiological effects. For example, each of the compounds shown here has
a nonpolar, planar, six-membered ring and substituents with similar polarities. They all have anti-inflammatory activity and are known
as NSAIDs (non-steroidal anti-inflammatory agents).
Salicylic acid has been used for the relief of fever and arthritic pain since 500 b.c. In 1897, acetylsalicylic acid (known by brand
names such as Bayer Aspirin, Bufferin, Anacin, Ecotrin, and Ascriptin) was found to be a more potent anti-inflammatory agent and
less irritating to the stomach; it became commercially available in 1899.
acetylsalicylic acid

Changing the substituents and their relative positions on the ring produced acetaminophen (Tylenol), which was introduced in
1955. It became a widely used drug because it causes no gastric irritation. However, its effective dose is not far from its toxic dose.
Subsequently, ibufenac emerged; adding a methyl group to ibufenac produced ibuprofen (Advil), which is a much safer drug. Naproxen
(Aleve), which has twice the potency of ibuprofen, was introduced in 1976.