Three names for one molecule
Take the common painkiller paracetamol. In the laboratory it has a precise chemical name no one says aloud. For everyday use it has a generic name — paracetamol (or acetaminophen in the United States) — which names the active substance itself. And it is sold under many a brand name such as Panadol or Tylenol, each owned by a company. Same molecule, several labels. The generic name belongs to the drug; the brand name belongs to a seller.
To stop the same drug having different generic names in different countries, the World Health Organization assigns each one an International Nonproprietary Name (INN) — a single, globally agreed, unmistakable label. The INN is what makes a prescription readable across borders and what lets the WHO build a list of essential medicines that every country can recognise.
Name endings reveal the family
Here is a gift hidden in the naming system: INN stems group drugs by family. Drugs in the same drug class — sharing a target or mechanism — usually share a recognisable ending. Spot the stem and you can often guess what a drug does even on first sight.
stem example INN drug class -------- ----------------- ------------------------- -pril enalapril ACE inhibitor (blood pressure) -sartan losartan angiotensin receptor blocker -olol propranolol beta-blocker -statin atorvastatin cholesterol-lowering statin -cillin amoxicillin penicillin antibiotic -mab adalimumab monoclonal antibody (biologic)