Your Brain, Your Choices: Effects of Drugs and Alcohol
Why does someone who has drunk too much walk unsteadily and make silly decisions? The answer lies in the brain – your body's control centre.
You will learn the jobs of the cerebrum and cerebellum, how alcohol, drugs and solvents harm the body, judgement and responses, and how to say no and get help. (Smoking has its own chapter, Effects of smoking.)
1. Meet Your Brain: the Cerebrum and the Cerebellum
The brain, protected by the skull, receives messages from the sense organs through nerves, decides what to do and sends messages to the muscles.
The cerebrum – the "thinking boss"
What it looks like: the largest part of the brain, on top, with a wrinkled, folded surface and left and right halves.
Its functions:
1. Thinking – solving a maths problem.
2. Memory and learning – learning words for a dictation.
3. Judgement – deciding if it is safe to cross the road.
4. Voluntary movement – movements you choose, like raising your hand.
5. Interpreting the senses – making sense of messages from the sense organs, e.g. recognising a red minibus or the smell of curry fish balls.
The cerebellum – the "balance coach"
What it looks like: much smaller, at the back of the head, below the cerebrum, with many fine folds.
Its functions:
1. Balance – keeping you steady on a moving MTR train.
2. Coordination of movement – making muscles work together smoothly and accurately, e.g. riding a bicycle.
The cerebrum decides "kick the ball"; the cerebellum makes the kick smooth without you falling over! Memory aid: picture the double L in cerebeLLum as two Legs standing steady.
Did you know? "Cerebellum" means "little brain" in Latin. Below the cerebrum and cerebellum, the brainstem joins the brain to the spinal cord and controls breathing and heartbeat.
Spot the part!
In a side view of the brain:
Large, wrinkled, dome-shaped, on top → cerebrum
Small, at the back and underneath, with fine folds → cerebellum
Stalk-like, joining the spinal cord → brainstem
Practice: A gymnast walks along a balance beam without wobbling – which part? (Cerebellum.) A student solves a riddle? (Cerebrum.)
How a response happens
Your eyes detect a ball flying towards you (a stimulus) and nerves carry messages to the brain. The cerebrum interprets this and decides to catch it; the cerebellum coordinates your hands. The catch is a response.
The time between stimulus and response is the reaction time. Anything that slows the brain makes it longer.
Try it: the ruler-drop test
A partner holds a 30 cm ruler with the zero mark between your open thumb and finger, then lets go without warning. You catch it and read how far it fell. Shorter distance = faster reaction (about 5 cm ≈ 0.1 s; about 20 cm ≈ 0.2 s). For a fair test, use the same hand and starting position, and repeat to find an average.
Key takeaway: The cerebrum handles thinking, memory, learning, judgement, voluntary movement and the senses; the cerebellum handles balance and coordination.
2. Alcohol: a Depressant
The alcohol in beer, wine and spirits is ethanol. It is absorbed quickly into the blood and reaches the brain within minutes; the liver then slowly breaks it down. Alcohol is a depressant: it slows down the brain and nerves.
Effects on judgement, coordination and reactions
Cerebrum: poor decisions, risk-taking, loss of self-control, unclear thinking, memory gaps, and senses interpreted less accurately (e.g. misjudging distances).
Cerebellum: staggering, losing balance, clumsiness and slurred speech (poorly coordinated mouth and tongue muscles).
Reactions: reaction time becomes longer. In the ruler-drop test, a person who has been drinking lets the ruler fall further.
Too much at once: alcohol poisoning
Drinking a lot in a short time can cause alcohol poisoning: vomiting, confusion, passing out and very slow breathing. It can kill. If someone cannot be woken up, call for emergency help at once and do not leave them alone.
Drink-driving: a deadly mix
A driver who has been drinking reacts more slowly (so the car travels further before braking), misjudges speed and distance, steers poorly and often feels overconfident.
Hong Kong law sets a legal limit for alcohol in a driver's breath or blood, and police carry out random breath tests. Never drink and drive, and never ride with a driver who has been drinking.
Long-term harm from heavy drinking
Liver: fatty liver, then permanent scarring (cirrhosis) and a higher risk of liver cancer. Brain: damaged brain cells, memory and learning problems. Others: high blood pressure, heart disease, stomach problems, some cancers and dependence.
Young people and the law
The brain keeps developing into the twenties, so alcohol can harm young people more. In Hong Kong, it is against the law for businesses to sell or supply alcoholic drinks to anyone under 18. Health experts advise young people not to drink at all.
Common mistake: "Coffee or a cold shower will sober a drunk person up." Wrong! Only time removes alcohol, as the liver breaks it down at a slow, steady rate. Coffee only makes someone feel more awake.
Key takeaway: Alcohol is a depressant that slows reactions and impairs judgement (cerebrum), balance and coordination (cerebellum). Heavy drinking damages the liver and brain.
3. Drug Abuse
A drug is any substance that changes how the body or mind works. Medicines are drugs that are safe when used as directed. Drug abuse means taking drugs for non-medical reasons (e.g. to get "high") or using medicines in the wrong way or amount. In Hong Kong, possessing or selling dangerous drugs is a serious crime.
Three main groups of abused drugs
Depressants slow the brain down – e.g. heroin, sleeping pills, large doses of some cough medicines (alcohol and solvents act this way too).
Stimulants speed the brain and body up – e.g. methamphetamine ("Ice"), cocaine.
Hallucinogens make a person see, hear or feel things that are not real – e.g. ketamine (also an anaesthetic), LSD. Some drugs, such as cannabis, have mixed effects (cannabis is often grouped with the hallucinogens).
Commonly abused drugs in Hong Kong
Cannabis – usually smoked. It harms memory, concentration and learning, slows reactions and coordination, and can cause anxiety and paranoia; regular use by teenagers is linked to mental health problems. In Hong Kong, cannabis is a dangerous drug, and since 2023 so is CBD (cannabidiol, a chemical found in cannabis), so CBD products are illegal too.
Ketamine – an anaesthetic abused as a sniffed powder. It causes hallucinations, confusion, poor coordination and numbness, so users may get hurt without feeling pain. Long-term abuse can badly damage the bladder (frequent, painful urination; the bladder can shrink) and harms memory.
Methamphetamine ("Ice") – a strong stimulant. It makes the heart race, raises blood pressure and stops sleep and appetite. It can cause aggression, hallucinations and paranoia; long-term use damages the heart, brain and teeth. It is highly addictive.
Cough medicine misuse – some cough medicines contain codeine. Drinking large amounts to get "high" causes drowsiness, confusion, slowed breathing and dependence.
How drugs harm the brain, body, judgement and responses
Brain and judgement: drugs disturb thinking, memory and judgement, so users take dangerous risks; hallucinogens make the cerebrum misinterpret the senses; some drugs trigger anxiety, depression or psychosis (losing touch with reality). Many upset the cerebellum, causing falls. Depressants slow responses; stimulants make them jumpy.
Body: damage to the heart, lungs, liver, kidneys, bladder and teeth. An overdose can cause unconsciousness or death, and street drugs often contain unknown substances.
Addiction: tolerance and dependence
Tolerance: with repeated use, the body gets used to a drug, so a person needs more and more for the same effect – raising the risk of overdose.
Dependence (addiction): the person feels unable to stop. Psychological dependence is a strong craving; physical dependence means stopping causes withdrawal symptoms such as shaking, sweating, sickness and anxiety. Addiction harms health, studies and family life – the safest choice is never to start.
Key takeaway: Drug abuse harms the brain, body, judgement and responses, and can lead to tolerance, dependence and overdose.
4. Solvent Abuse
Solvent abuse means breathing in vapour from glue, paint thinner, lighter gas or aerosol sprays to get "high". Solvents act like depressants, causing dizziness, slurred speech, staggering and sometimes hallucinations, much like being drunk. Even the first time, sniffing can make the heart beat irregularly and stop, causing sudden death. Long-term abuse damages the brain, liver and kidneys.
Key takeaway: Sniffing solvents can kill, even the first time.
5. Saying No and Getting Help
Refusal skills
1. Say "No" clearly and firmly – "No, thanks. I don't drink."
2. Give a reason – "I have football training tomorrow."
3. Suggest something else – "Let's get bubble tea instead."
4. Walk away – if they keep pushing, leave. Real friends respect your choices.
Memory aid: No – Reason – Swap – Walk away: "Never Risk Something Worse."
Where to get help
Talk to a trusted adult – a parent, teacher, school social worker or doctor. Hong Kong also has free, confidential counselling services, which a school social worker can help you reach.
Signs a friend may need help: sudden mood changes, falling grades, losing interest in hobbies. Asking for help early is a sign of strength.
Key takeaway: Say no clearly, and talk to a trusted adult when you need help.
Common Mistakes to Avoid
1. Balance and coordination belong to the cerebellum, not the cerebrum.
2. "Alcohol is a stimulant because drunk people get lively." Wrong – it is a depressant that weakens self-control.
3. "Natural drugs like cannabis are safe." Wrong.
4. "Trying once won't hurt." Wrong – solvents and overdoses can kill the first time.
Quick Review
1. Cerebrum (largest, on top): thinking, memory, learning, judgement, voluntary movement, interpreting senses.
2. Cerebellum (back, below): balance and coordination.
3. Alcohol is a depressant: slower reactions, poor judgement and coordination. Never drink and drive.
4. Heavy drinking damages the liver and brain; no alcohol sales to under-18s in Hong Kong.
5. Drugs and solvents harm the brain, body, judgement and responses, and cause tolerance and dependence.
6. Say no, and talk to a trusted adult.
Now you know how your brain works and how to protect it – you've got this!