One symptom, one body system
Open most home medicine cabinets and you find a small crowd: something for heartburn, something for a blocked or runny nose, an inhaler for wheezing, maybe a tablet for travel sickness or an upset gut. It can look like chaos. But there is a tidy idea underneath. A drug is simply a substance that changes how some part of the body works, and most everyday medicines are sorted by which symptom in which system they fix. We call such a family a drug class — a group of medicines that share a way of working and a job to do.
The reason that helps a beginner is this: you rarely have to memorise hundreds of names. If you know the system (gut, lung, nose) and the goal (less acid, open airways, calm the cough), you can usually predict what a drug does before you read a word about it. The thing a drug is officially used for is its indication.
A tour of the four neighbourhoods
The gut. Too much stomach acid causes heartburn and ulcers, so we have acid-fighters: an antacid neutralises acid that is already there, while a proton-pump inhibitor and an H2 antagonist tell the stomach to make less. Further down, an antiemetic stops nausea and vomiting, a laxative relieves constipation, and an antidiarrhoeal slows things down when they are too fast.
The lung. In asthma the airways tighten. A bronchodilator relaxes the muscle and opens them; the most familiar kind is a beta-2 agonist you puff from an inhaler. To calm the underlying swelling we add an inhaled corticosteroid, and sometimes a leukotriene antagonist tablet.
The nose and throat. An allergy releases histamine, so an antihistamine blocks it and dries up the sneeze and itch. A nagging dry cough can be eased by an antitussive. These are the medicines you grab in hay-fever season or with a cold.