Health and drugs · System
Alcohol and smoking
Two drugs that are legal for adults, sold openly, and between them responsible for more illness in this country than every illegal drug put together. Both are worth understanding as biology before anyone argues about them.
Start here
Black coffee, a cold shower, a walk in the fresh air.
Three things people are certain will sober someone up. Two of them do nothing at all to the alcohol in their blood, and the third does nothing either. The alcohol is not on their skin or in their lungs — it is in the blood, and only one organ can take it out.
What actually lowers the alcohol in someone's blood?
The liver, working at its own fixed rate of roughly one unit an hour. Nothing raises that rate. Coffee makes a drunk person more awake without making them less drunk, which is worse than useless — it is an alert person with the judgement and reaction times of a drunk one.
At the bench · one liver, one clock
The liver cannot be hurried
clock not started
Build an evening's drinks for someone else, pick something to speed the clearing up, then run the clock. Every trick on this bench is one people genuinely believe in. Only one of them changes anything, and not the thing they think.
Add a drink
And to sober up faster
4 units drunk
4 hours to clear
Alcohol still in the blood
0 hours elapsed · 4 units left
The only thing on this bench that moves the number. One unit an hour, set by how much enzyme the liver has, and it is the same rate whether the person is asleep, awake, worried or in a hurry.
Caffeine is a stimulant, so they feel more awake. The alcohol is untouched. You have converted a sleepy drunk person into an alert drunk person, and the alert one is the one who thinks they can drive.
Cold skin, sharp intake of breath, no change whatever in the blood. The liver is not on the outside of the body.
Only a trace of alcohol leaves through the lungs — which is exactly why a breath test works, and why breathing harder cannot clear it. The rest goes through the liver.
This one does something real, and it is not what people claim. Food in the stomach slows absorption, so the peak in the blood is lower and the person is less impaired at their worst. The total amount to break down has not changed, so the hours have not changed.
Genuinely helps the dehydration, the headache and the thirst. Does nothing at all to the alcohol — you cannot dilute your way out of a fixed amount.
Not one night — years of nights
Each one damages a different set of organs.
Depressant · Alcohol, over years
Liver — Working cells are replaced by scar tissue. Early damage recovers if drinking stops; scarring does not. Brain — Tissue is lost, and memory and judgement are affected long before anyone would call the person unwell. Stomach and gut — Lining irritated and inflamed, which is why heavy drinkers bleed and vomit. Whole body — Raised risk of several cancers, high blood pressure and stroke — and, because judgement goes first, a large share of accidents and injuries.
Stimulant plus a poison plus tar · Tobacco smoke, over years
Brain — Nicotine reaches it in about ten seconds and the reward pathways adapt to expect it. That adaptation is why stopping is hard, and it is not what causes the disease. Blood — Carbon monoxide binds to haemoglobin in place of oxygen and holds on. Less oxygen is delivered to every tissue, and a smoker is out of breath sooner for that reason alone. Heart and vessels — Vessels narrow, blood pressure rises, and clots form more readily — heart attack and stroke risk both climb. Airways and alveoli — Damaged by tar and by the other substances in the smoke.
Key fact
Alcohol is a depressant: it slows the nervous system, and the liver clears it at about one unit an hour whatever anyone does. Nicotine is a stimulant and is what makes smoking hard to stop; carbon monoxide in the same smoke takes the places oxygen should occupy in the blood.
Think again
“Coffee, a cold shower or fresh air will sober you up.”
Alcohol leaves the body almost entirely through the liver, which breaks it down at a rate set by how much enzyme it contains — about one unit an hour, and that rate does not respond to encouragement. Cold water on the skin does not reach the liver. Breathing harder does not either, because only a trace leaves through the lungs, which is precisely why a breath test can measure what is in the blood. Coffee is the dangerous one, because it works on a different organ: caffeine is a stimulant and makes the person feel awake, so the outward signs of being drunk fade while the impairment is untouched. Someone who feels capable and is not is more likely to drive than someone who feels terrible. The only variable that matters is time, and a large evening does not fit inside a night's sleep: six units finished at midnight are not cleared until around six in the morning.
“A few cigarettes now and then is basically fine, and filters make them safer.”
There is no threshold below which smoke stops damaging tissue — the risk rises from the first cigarette, and social smokers develop dependence too, because nicotine's grip is about how quickly it reaches the brain rather than how many are smoked in a week. The filter is the more interesting half of the claim. It removes some tar, and it was introduced when the link with cancer became public, but it does nothing to carbon monoxide, and by making the smoke smoother it encourages deeper inhaling. Ventilation holes in the paper also deflate the tar figures measured by machines, below what a smoker whose fingers and lips cover the filter actually receives. So a filter changes the taste, changes the number in the test, and does not make the habit safe. What smoke does to the airways and to the alveoli themselves is the subject of Exercise, asthma and smoking.
Mastery ladder
Not started yet.
Rungs 3 and 4 you mark yourself.
Rung 1 · Read the clock
Someone drinks six units, finishing at midnight. Roughly when is the alcohol cleared from their blood?
Rung 2 · The one that catches people
A drunk person drinks two strong black coffees. What has changed?
Rung 3 · Explain the carbon monoxide
A smoker gets out of breath climbing stairs sooner than a non-smoker of the same fitness, even before any lung damage has developed. Explain why, using what the blood carries.
Rung 4 · Take it somewhere new
An energy drink is advertised as a mixer for spirits, and someone claims it "keeps you sober because caffeine cancels out alcohol". Judge the claim using the two drug classes, say what actually happens to the person, and explain why this combination is more dangerous than the alcohol alone.
Key note
Alcohol is a depressant. It slows nerve signals, so reactions, coordination and judgement all worsen, and only the liver removes it — at about one unit an hour, whatever anyone tries. Long term it scars the liver and damages the brain. In tobacco smoke, nicotine is the stimulant that makes stopping hard, carbon monoxide takes oxygen's place in the blood, and tar and the other substances damage the airways.
Going further
A vape has no tar and no carbon monoxide, because nothing is burned — so a smoker who switches removes two of the three harms in the list above. It still delivers nicotine, often faster and in larger amounts than a cigarette, so the dependence is the same or stronger, and a person who has never smoked gains nothing at all and takes on the dependence for nothing. The honest position is the one a scientist has to be comfortable with: vapes are very likely less harmful than cigarettes and are not known to be safe, because the long-term studies do not exist yet — the devices are too new for anyone to have used one for forty years. Selling either to under-18s is illegal in the UK. This is a good example of a question where the evidence is genuinely incomplete and where less harmful than the worst option and harmless are miles apart.
If any of this is about you or someone you know
This lesson covers the biology only. Pressure from friends, family drinking, and what the law says belong in your PSHE and RSE lessons, and they are worth raising there. If something here is about your own home or your own habits, talk to a trusted adult, the school nurse, a pharmacist or a GP — stopping smoking in particular is one of the few things where free NHS help genuinely doubles the success rate. Your school's PSHE materials list the national confidential services by name.
Before this lesson
Connects to
At GCSE this becomes
- Risk factors for non-communicable disease, the difference between correlation and cause in population studies, and how a causal link is established.
Where to next
Ask Mr Badmus AI
Want to work out why the liver's rate cannot be hurried?
If any of this is about you or someone you know, talk to someone you trust — a parent or carer, a teacher, your school nurse, a pharmacist or your GP. Out of school hours: Childline — 0800 1111, free and confidential. FRANK — 0300 123 6600.
The clock is a simplified model: one unit an hour, cleared in whole hours, ignoring body mass, sex, medication, food already eaten and how quickly the drinks were finished. Real clearance varies between people and is slower, not faster, than this model when the liver is already damaged. It is a teaching model and must not be used to judge whether anyone is fit to drive.
Lesson content © MrBadmusAI.