KS3 · Biology

Recreational drugs: stimulants

Drop a ruler and catch it: that gap is your reaction time. One person's caffeine results look convincing. How far can one person's results really go?

Biology · Stimulants

One person's result: how far can it take you?

The claim

Caffeine will decrease everyone's reaction time.

Place each piece of evidence to load the balance. Mark the strong ones — they count double.

  1. In one sample from a ruler-drop test, one person's mean reaction time was 211 ms without caffeine and 193 ms with caffeine. That is a shorter time with caffeine.

    Evidence 1: does it support or challenge the claim?

  2. Caffeine is absorbed into the blood from the gut, and as a stimulant it speeds up the messages sent from the brain to the rest of the body.

    Evidence 2: does it support or challenge the claim?

  3. Stimulants can give quicker thinking and reaction times.

    Evidence 3: does it support or challenge the claim?

  4. Only one person was tested.

    Evidence 4: does it support or challenge the claim?

  5. The sample is very small.

    Evidence 5: does it support or challenge the claim?

  6. Other factors, such as body mass or how tired the person was, were not taken into account.

    Evidence 6: does it support or challenge the claim?

How the ruler-drop test works

Step through it. Notice how much of the method is about keeping things the same.

Biology · Drugs

Medicine, legal stimulant or illegal stimulant?

Pick an item, then pick where it belongs. Drugs can be sorted as stimulants or depressants, and every stimulant here speeds up messages from the brain to the body.

Still to sort

Medicine (0)

Used to treat illness.

Where the line is: A medicine treats an illness. A recreational drug is taken because it makes a person feel different, not to treat an illness.

Contains a legal stimulant (0)

Caffeine is a legal stimulant.

Where the line is: Legal and illegal stimulants are both stimulants. What separates them here is the law.

Illegal stimulant (0)

Cocaine and ecstasy are illegal stimulants.

Where the line is: These are illegal and class A, the class considered the most dangerous and harmful.

8 of 8 still to sort.

Caffeine vs cocaine

CaffeinevsCocaine

Both are stimulants and both come from plants. Read down the rows and see where they split.

Focus

Where it comes from

Caffeine

A plant: coffee beans

Cocaine

A plant: the leaves of the coca plant

The insight

Same starting point, a plant. Their places in the law and their harms still turn out very different.

The law

Caffeine

Legal, and easy to get

Cocaine

Illegal, and class A: the class considered the most dangerous and harmful

Harms

Caffeine

Too much can lead to an increased heart rate, insomnia and digestive issues

Cocaine

Can cause a stroke or heart attack. In high doses an overdose can lead to coma or death

Addiction

Caffeine

Can lead to psychological and physical addiction

Cocaine

Highly addictive

Biology · Addiction

Why can a legal drug still be hard to stop?

2 stages are missing. Use the rest of the loop to work out which goes where.

  1. Stage 1: Using caffeine

    Caffeine is legal and easy to get, but it can lead to psychological and physical addiction.

  3. Stage 3: Withdrawal

    A person who stops using caffeine may have headaches, anxiety and irritability, feel sluggish and tired, and have decreased alertness.

…and stage 4 leads back to stage 1.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

What a stimulant does to your brain's messages, and how far one test can prove it.

What you need to know

  • A stimulant speeds up the messages sent from your brain to the rest of your body, along the nerves.
  • That can make you feel more awake, alert, confident and energetic, and can give quicker thinking and reaction times.
  • Have a goYour mate swears a stimulant would make him slower to react when a ruler drops. Back him up, or put him straight?

    Put him straight. A stimulant speeds up messages from the brain to the body.

    He has the direction backwards: stimulants can give quicker reaction times, not slower ones.

  • Medicines such as ibuprofen and antibiotics treat illness. Recreational drugs are taken because they make you feel different. Drugs can also be sorted as stimulants or depressants.
  • Stimulants can be legal, like caffeine, or illegal, like cocaine and ecstasy. Caffeine and cocaine both come from plants.
  • Have a goCaffeine and cocaine both come from plants. Does that mean the law treats them the same way?

    No. Caffeine is legal, but cocaine is illegal.

    Both are stimulants that come from plants, yet stimulants can be legal or illegal.

  • Caffeine is readily absorbed into the blood from the gut. You find it in coffee, tea, cocoa beans (used for chocolate) and energy drinks.
  • In the ruler drop test you read off where the ruler was caught, look up the time and repeat five times. The mean is the results added up, divided by the number of repeats.
  • In one sample, one person's mean reaction time was 211 ms without caffeine and 193 ms with it. That fits caffeine speeding up messages.
  • One person's result can't show it for everyone. Body mass and tiredness weren't taken into account, and the sample is very small, so the test needs repeating with a large number of people.
  • Have a goA friend's reaction was quicker after a coffee, so she announces that coffee makes everybody faster. Is that a fair step?

    No. One friend's result can't show what happens for everybody.

    One result is one person's. It needs repeating with a large number of people to be representative.

  • Cocaine and ecstasy are illegal class A drugs, the class considered most dangerous and harmful. Cocaine can cause a stroke or heart attack, and ecstasy can interfere with the body's water control.
  • Caffeine is legal, but it can still cause addiction and harm. Substance abuse, the excessive or addictive use of a drug, can harm health and relationships.

The big picture

A stimulant speeds up the messages sent from the brain to the rest of the body. Caffeine is a legal stimulant, while cocaine and ecstasy are illegal class A stimulants. One person's ruler-drop result fits caffeine shortening reaction time, but it cannot show that caffeine does this for everyone. Legal stimulants such as caffeine can still lead to addiction and harm.

Key points

1A stimulant speeds up the messages sent from the brain to the rest of the body (along the nerves).
2Stimulants can make a person feel more awake, alert, confident and energetic, with quicker thinking and reaction times. They can be legal (caffeine) or illegal (cocaine, ecstasy).
3A mean is found by adding up all the results and dividing by the number of repeats.
4One person's results can't show that caffeine will decrease everyone's reaction time. The test needs repeating with a large number of people to be representative.
5Cocaine and ecstasy are illegal class A drugs. Cocaine can cause a stroke, a heart attack, or an overdose that can lead to coma or death. Ecstasy can make people feel energised but can interfere with homeostatic control, especially water control, and this has in some cases led to death.
6Addiction is not having control over using something that could harm you. Caffeine is legal and easy to get but can lead to psychological and physical addiction, and too much can cause an increased heart rate, insomnia and digestive issues.
7When a person stops using caffeine they may get withdrawal: headaches, anxiety, irritability, feeling sluggish and tired, and decreased alertness. This can lead them back to using it.

Worked example

Problem

A person does five ruler-drop reaction time tests and gets 200, 190, 210, 180 and 220 ms (made-up practice numbers). Find the mean reaction time.

⚠ Watch out

Two traps. One: a faster time with caffeine for one person is read as proof that caffeine speeds up everyone. Two: 'caffeine is legal, so it can't hurt or be addictive'. Caffeine can still lead to addiction and harm.

🧠

Memory hook

One result is a clue, not a verdict. And 'legal' is a label from the law, not a promise that something is harmless.

✓

Check yourself

A friend says: 'Caffeine is legal, so it's perfectly safe.' Using what you know about addiction and what happens when someone stops, how would you answer them?

Flashcards

(15)
What does a stimulant do?
It speeds up the messages sent from the brain to the rest of the body, along the nerves.
Name some effects stimulants can have.
They can make a person feel more awake and alert, more confident and more energetic, and can give quicker thinking and reaction times.
How is a medicine different from a recreational drug?
A medicine, such as ibuprofen or an antibiotic, treats illness. A recreational drug is taken because it makes a person feel different, not to treat an illness.
Give a legal stimulant and two illegal stimulants.
Legal: caffeine. Illegal: cocaine and ecstasy.
Where is caffeine found, and how does it reach the blood?
In coffee, tea, cocoa beans (used for chocolate) and energy drinks. It is readily absorbed into the bloodstream from the gut.
In the ruler drop test, what do you do with the distance the ruler fell?
Look it up in a reaction time table to find the reaction time.
How do you calculate a mean?
Add up all the results, then divide by the number of repeats.
Why can one person's reaction time results not prove caffeine works for everyone?
The sample is very small and other factors, like body mass or tiredness, weren't taken into account. It needs repeating with a large number of people.
What does 'class A' mean?
Class A drugs are considered the most dangerous and harmful. Cocaine and ecstasy are class A.
What serious harms can cocaine cause?
A stroke or a heart attack. In high doses an overdose can lead to coma or death.
What is ecstasy (MDMA)?
A man-made, illegal class A stimulant. It can interfere with homeostatic control, especially water control, and this has in some cases led to death.
What harms can too much caffeine cause?
An increased heart rate, insomnia and digestive issues.
What is addiction?
Not having control over using, taking or doing something that could cause you harm. An addicted person feels they cannot stop even though they know it is harming them.
What is substance abuse?
The excessive or addictive use of a drug. Both legal and illegal drugs can be misused, and it can cause physical and mental health issues and affect relationships.
What is caffeine withdrawal, and what can it lead to?
After stopping, a person may get headaches, anxiety, irritability, feel sluggish and tired, with decreased alertness. This can lead them to go back to using caffeine.

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.

Learning with Lightbulb is opening soon

You can use this lesson now. Join the waitlist and we'll let you know when the full Lightbulb experience is ready.

Keep me posted

More KS3 Biology topics

See the full KS3 Biology curriculum →

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.