What is a drug?
A drug (medicine) is a chemical that changes what the body does. Some drugs cure a disease, some stop pain, some prevent a disease, some replace something the body lacks (like insulin).
Drugs come from plants, from living things such as moulds, or are made in factories.
Drug action
Cells have receptors: tiny sockets on the cell surface. A drug molecule fits a receptor the way a key fits a lock. When it fits, the cell is told to do something, or told to stop.
Some drugs do not use receptors. An antacid, for example, just neutralises extra stomach acid. Antibiotics act on germs, not on our cells.
Drugs and body responses
The body's response depends on the dose, the amount taken. Small dose: little effect. Right dose: the wanted effect. Too large a dose: harm.
The same drug does not work the same in everyone. Age, weight, other illness, liver and kidney strength and other drugs all change the response. Children and older people often need smaller doses.
Body responses can be: the main effect (what we want), a side effect (an extra, unwanted effect), an allergy (rash, swelling, breathing trouble), or tolerance (the body needs more for the same effect).
Drug therapy
Drug therapy means treating a person with drugs. A nurse follows the "five rights": right patient, right drug, right dose, right route (mouth, injection, skin, inhaler) and right time.
After a dose, the level in the blood rises, then slowly falls as the liver and kidneys remove the drug. So doses are repeated at set times to keep the level in the helpful zone.
Nurses also check the person after the dose: Did it work? Is there a rash, vomiting or sleepiness? They report problems at once and keep a record.
Health damage caused by drugs
- Side effects and poisoning from too large a dose or the wrong drug.
- Allergy to a drug, which can be serious.
- Resistance: germs survive half-finished antibiotic courses and become hard to kill.
- Dependence (addiction): the body or mind cannot do without the drug. Examples are some painkillers, sleeping pills, alcohol and tobacco.
- Drug misuse: taking medicine without need, or taking someone else's.
Safe habits: take medicine only as prescribed, never share it, store it away from children, check the expiry date.
Try it
Open the 3D. Step 2: drag the dose slider from 0 to 10 and say aloud at which numbers the gauge is blue, green and red. At home: look at a medicine strip. Find the dose, how often, and the expiry date.
Key formulas and definitions
- Key terms: drug = chemical that changes body function; receptor = socket on a cell; dose = amount given
- Five rights: patient, drug, dose, route, time
- Too little dose = no effect; right dose = benefit; too much = harm
- Side effect = unwanted extra effect; allergy = body defence reacts to the drug
Worked examples
1. A doctor says "one tablet every 8 hours". How many tablets in one day?
24 hours ÷ 8 hours = 3 doses, so 3 tablets in a day.
2. A child had fever medicine at 8 am. The next dose is due after 6 hours. At what time?
8 am + 6 hours = 2 pm.
3. Why must an antibiotic course be finished even when the child feels well?
Feeling well only means most germs are dead. A few strong germs may be left. If the medicine is stopped, they multiply and become resistant, so the next treatment may fail.
Common mistakes
- Thinking a double dose cures twice as fast. It adds risk, not speed.
- Stopping antibiotics when the fever goes.
- Using old medicine or a friend's medicine for a new illness.
- Believing "natural" always means safe. Any strong drug, natural or made, can harm.