Who this is for: Cambridge IGCSE Biology (0610) students who want drugs — antibiotics, tobacco, alcohol and misuse — to become reliable marks instead of a list of effects they cannot link to body systems.
What query it owns: how to understand and revise drugs in Cambridge IGCSE Biology.
Why this is safe: this page owns the drugs revision-guide angle, while Tutopiya’s Drugs subtopic page owns the learning resource and the free Drugs quiz owns the practice.

Drugs are substances that alter the way the body works. Cambridge IGCSE Biology (0610) tests whether you can explain the effects of antibiotics, tobacco, alcohol and heroin, describe the consequences of drug misuse, and state why antibiotics do not work on viruses. This guide covers the syllabus content, harmful vs beneficial drugs, and the question types that appear every year.

Key takeaways

• Antibiotics kill bacteria but are ineffective against viruses.
• Misusing antibiotics contributes to antibiotic resistance in bacterial populations.
• Tobacco smoke contains tar (causes cancer), nicotine (addictive) and carbon monoxide (reduces oxygen transport).
• Alcohol is a depressant affecting reaction time, coordination and the liver.
• Heroin is addictive and depresses the nervous system, slowing reactions and breathing.

What are drugs in Cambridge IGCSE Biology?

A drug is a substance taken into the body that modifies or affects chemical reactions. Some drugs are beneficial (e.g. antibiotics treating bacterial infections); others are harmful when misused (e.g. heroin, excessive alcohol). The syllabus requires you to know specific effects of tobacco, alcohol and heroin, and to explain why antibiotic resistance develops when antibiotics are overused or not completed.

You can read the full explanation, worked examples and notes on Tutopiya’s Drugs subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Antibiotics	Kill bacteria, not viruses	”Explain why antibiotics don’t treat flu”
Antibiotic resistance	Bacteria survive → reproduce → resistant population	”Explain how resistance develops”
Tobacco effects	Tar, nicotine, carbon monoxide	”Describe effects of smoking”
Alcohol effects	Depressant; liver damage; slower reactions	”State effects of alcohol”
Heroin effects	Addictive; depresses nervous system	”Describe effects of heroin”

Effects of specific drugs

Drug / substance	Key harmful effects
Antibiotics (misuse)	Resistant bacteria survive; infections harder to treat
Tobacco (tar)	Causes bronchitis, emphysema, lung cancer
Tobacco (nicotine)	Addictive
Tobacco (carbon monoxide)	Combines with haemoglobin, reducing oxygen transport
Alcohol	Depressant; slower reactions; liver damage (cirrhosis)
Heroin	Highly addictive; depresses nervous system; slows breathing

Drugs in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical drugs stem
Define	Precise syllabus definition	”Define a drug.”
Describe	Effects step by step	”Describe the effects of tobacco smoke.”
Explain	Cause and effect	”Explain how antibiotic resistance develops.”
State	Short factual answer	”State why antibiotics are not used for viruses.”
Suggest	Apply to scenario	”Suggest why a patient should finish the full course.”

Worked exam-style stems (how to answer the wording)

1. “Explain why antibiotics are not effective against viruses.” Antibiotics kill bacteria by targeting bacterial cell structures; viruses reproduce inside host cells and lack these structures, so antibiotics cannot destroy them. Mark-scheme reward: bacteria vs virus mechanism.
2. “Describe the effects of carbon monoxide in tobacco smoke.” Carbon monoxide combines with haemoglobin in red blood cells → reduces oxygen transport → less oxygen reaches tissues. Reward: haemoglobin + reduced oxygen.
3. “Explain how antibiotic resistance develops.” Antibiotics kill most bacteria; resistant bacteria survive → reproduce → population of resistant bacteria increases → antibiotic becomes ineffective. Reward: survival → reproduction → resistance.

When you can recognise the wording instantly, work the full set on the Drugs topical past paper questions and the Drugs quiz to lock the definitions in.

How drugs connect to the rest of the syllabus

Drugs link to Medicinal Drugs (drug development and testing), Diseases and Immunity and Antibiotic Resistance flashcards. The Cambridge IGCSE Biology resource hub links every Drugs subtopic.

Common mistakes students make

• Saying antibiotics kill viruses (they only kill bacteria).
• Omitting carbon monoxide’s effect on haemoglobin in tobacco questions.
• Describing alcohol as a stimulant (it is a depressant).
• Explaining resistance without mentioning survival and reproduction of resistant bacteria.
• Confusing addiction (nicotine, heroin) with physical damage (tar, liver).

When you need more support

If drugs questions keep costing marks — especially antibiotic resistance explain chains — work through the Drugs topical past paper questions and the Drugs quiz, then get focused help from a Cambridge IGCSE Biology tutor.

Frequently asked questions

Is drugs hard in Cambridge IGCSE Biology? The content is factual, but marks are lost when students say antibiotics work on viruses or omit specific tobacco components (tar, nicotine, carbon monoxide).

Why do antibiotics not work on viruses? Antibiotics target bacterial structures; viruses lack these and reproduce inside host cells.

What is antibiotic resistance? When bacteria survive antibiotic treatment, reproduce and pass on resistance, making the antibiotic ineffective over time.

How do I revise drugs effectively? Learn each drug’s effects in a table, practise resistance explain chains, then take the Drugs quiz.

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