KS3 · Biology
Recreational drugs: depressants
Your brain sends your body messages all day long: move this muscle, say that word, catch that cup. Now imagine every one arriving a little late.
Biology · Types of drug
Which group does each drug belong to?
Pick a drug, then pick the group it belongs in. Watch Valium: it is the one that sits on a line.
Still to sort
Medicine (0)
Taken to help when a person is ill.
Where the line is: Some drugs sit on a line: benzodiazepines such as Valium are legal when prescribed by a doctor, but illegal if obtained or used any other way.
Legal recreational drug (0)
Legal, and taken for how it makes a person feel rather than to treat illness.
Legal, but age-limited (0)
A recreational drug that is legal but controlled by an age limit.
Illegal (0)
A recreational drug that is against the law.
Medicines treat illness. Recreational drugs are taken for how they make a person feel. Sort each drug, then read why.
Biology · Long-term harm
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Switch the liver view, then tap a part to read what the lesson says about it.
A healthy liver. It can regenerate itself.
Switch between a healthy and a scarred liver, then tap a part of the body.
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
What you need to know
- Stimulants speed up the messages sent from the brain to the body. Depressants do the opposite.
- So a depressant slows down the messages sent from the brain to the body, along the nerves.
- Depressants slow thinking and slow reaction time, which is how quickly you respond to something that happens around you.
Have a goA car pulls out in front of someone whose brain-to-body messages are slowed. Do they respond sooner or later than usual, and what is that called?
Later than usual. That is a slower reaction time.
Reaction time is how quickly you respond to something that happens, so slowed messages make the response later, not sooner.
- They can also leave a person feeling relaxed and less inhibited (less held back), and make speech slow and drowsy-sounding.
- Alcohol, benzodiazepines such as Valium, and GHB are examples of depressants. GHB is illegal.
- Alcohol is a legal, controlled drug. In the UK, a person must be over 18 to buy it.
- Too much alcohol can slow reactions, slur speech and cause loss of muscle control, such as not being able to walk well.
Have a goSlurred speech and not walking well look like two different problems. What one thing do they share as a cause?
Alcohol slowing down the messages from the brain.
Speech and muscle control both depend on messages from the brain, so slowing those messages affects both at once.
- Slower reactions raise the risk of an accident when driving or doing other activities, such as work.
- The UK has a legal drink-drive limit on blood alcohol level. Police can check it with breath, blood or urine tests.
- Alcohol can be addictive: a person can find they need to have it all the time.
- Long-term alcohol use can damage the brain and the liver. Drinking alcohol is also a risk factor for many cancers, including bowel cancer.
- The liver can regenerate itself, but prolonged alcohol abuse can scar it permanently. Cirrhosis is when it can no longer function properly.
Have a goThe liver can regenerate itself. So why can prolonged alcohol abuse still leave it permanently damaged?
It can scar the liver, and that damage is permanent: the liver cannot repair it.
Being able to regenerate does not mean being able to undo every kind of damage, and scarring is the kind it cannot repair.
- A risk factor raises the chance of a disease. It does not mean a person will definitely get it.
- Being legal does not make alcohol less harmful: the WHO estimated that about 5% of all deaths are related to alcohol.
The big picture
A depressant slows down the messages sent from the brain to the body. That one slowing explains why alcohol slows thinking and reaction time, slurs speech and weakens muscle control, and why drinking raises the risk of an accident. Being legal does not make alcohol safe: it can be addictive, and long-term use can damage the brain and liver.
Key points
Worked example
Problem
Explain why someone who has drunk too much alcohol may not be able to walk well.
⚠ Watch out
Mixing up the direction. Stimulants speed messages up and depressants slow them down. In the web the arrows also run one way: slowed messages lead to a slower reaction time, which leads to a higher accident risk, and never the other way round.
Memory hook
Think of a slow courier. A depressant slows the courier that carries messages from your brain to your body, so every delivery arrives late. (The picture is just a memory aid: the courier is not a real part of the body.)
Check yourself
Cover the web and say it aloud: what does a depressant do, which four effects follow from it, and which of those effects leads on to a higher accident risk?
Flashcards
(15)Stimulant or depressant: what is the difference?
What is reaction time?
Besides slower thinking and slower reaction time, what else can depressants do?
Name three examples of depressants.
What is the difference between a medicinal drug and a recreational drug?
Give an example of a legal, an age-limited and an illegal recreational drug.
When are benzodiazepines such as Valium legal?
Name three short-term effects of drinking too much alcohol.
How can police check the UK legal drink-drive limit?
What does it mean to say alcohol can be addictive?
Which two body parts can long-term alcohol use damage?
What is liver cirrhosis?
What is foetal alcohol syndrome, and how does it happen?
What is a risk factor?
Alcohol is legal. Does that make it less harmful?
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
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How this lesson was checked. This KS3 Biologylesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 9 October 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.