0–0.05% BAC
Changes may be subtle
Relaxation and talkativeness may appear, while precision of movement, divided attention and accurate judgement already begin to weaken.
Alcohol and the body
What does alcohol do to the body over the course of one evening?
From barely noticeable relaxation to the point where the brain can no longer regulate breathing properly. See what may change as blood alcohol concentration rises — and why the way you feel is not a reliable measure of sobriety.
From the first changes to poisoning
The higher the concentration, the less ‘stimulation’ and the more suppression
Alcohol is a central nervous system depressant. The initial sense of energy mainly comes from weaker restraint and inhibition. As the concentration rises, alcohol increasingly slows the brain and functions that are not under conscious control.
0.05–0.1% BAC
Confidence rises faster than ability
Reaction time, coordination and judgement deteriorate. A person may feel more at ease even as they objectively make more mistakes.
0.1–0.2% BAC
Control clearly weakens
Unsteady walking, slurred speech, strong mood swings, memory problems and declining awareness of the situation may occur.
0.2–0.3% BAC
The risk of severe poisoning grows
Vomiting, hypothermia, confusion, double vision, memory gaps, profound drowsiness or periods of unconsciousness may occur.
0.3–0.4% BAC
An immediately life-threatening state
Profound drowsiness, stupor, weakened reflexes, falling temperature and blood pressure, and increasingly shallow breathing may occur.
above 0.4% BAC
Coma and death are real risks
Alcohol can suppress the centres that control breathing, heart rate and temperature. There is no single threshold that is fatal for everyone.
The ranges draw on clinical descriptions from NLM, NIAAA and SAMHSA. They are not intended for self-diagnosis or decisions about driving. Severe symptoms require action regardless of a breathalyzer reading.
The first several dozen minutes
Alcohol does not wait in the stomach. It quickly reaches the blood and brain
Ethanol is a small molecule that readily crosses cell membranes. Some is absorbed in the stomach, but most is absorbed in the small intestine. Food can therefore delay stomach emptying, flatten the peak concentration and move it later in time — but it does not neutralise alcohol already consumed.
For someone drinking on an empty stomach, the concentration may peak sooner; after a meal, later. This still matters after the last drink: alcohol remaining in the stomach and intestines may continue entering the blood. That is why a person who has stopped drinking or fallen asleep can still get worse.
Pace
Drinking quickly can raise the concentration before the body has time to respond.
Food
Food usually slows absorption, but it does not remove alcohol from the body.
Body composition
The amount of water in the body affects the concentration produced by the same dose.
Medicines and other substances
Opioids, sleeping medicines and sedatives can dangerously intensify suppression.
Cheers · during the evening
You do not have to reconstruct the evening from memory
Log drinks as you go and follow the estimated blood alcohol trend and the forecast return to zero.
The brain gives away the change first
Caution disappears first. Visible loss of control comes later
Alcohol disrupts communication between nerve cells. Among other things, it weakens functions of the prefrontal cortex — the area needed for planning, anticipating consequences and inhibiting impulses. This explains the paradox of the first phase: a person may feel more confident at exactly the point when their judgement is becoming less accurate.
Later, reaction time, visual tracking, precision of movement and balance are increasingly affected. Speech may become slurred and emotions may change abruptly. At high concentrations, alcohol also suppresses the areas responsible for consciousness and automatic functions such as breathing and temperature regulation.
Not only the brain
What is happening to the rest of the body at the same time?
Blood vessels in the skin widen, so the face may flush and a false sensation of warmth can appear. In reality, the body loses heat faster, increasing the risk of hypothermia at high doses. Alcohol can also increase urination and contribute to dehydration, but thirst the next day is not a simple measure of alcohol concentration.
The stomach and intestines may react with irritation, nausea and vomiting. The heart may beat faster or irregularly. When the gag reflex is impaired, an unconscious person can choke on vomit. Combining alcohol with opioids, benzodiazepines or sleeping medicines further increases the risk of respiratory suppression.
Do not wait for a ‘certain’ reading
Warning signs that mean you should call for help
Call for help if a person is confused, cannot be woken, loses consciousness, has a seizure, repeatedly vomits, breathes slowly or irregularly, or is very pale, blue, cold or clammy. Do not assume they can simply ‘sleep it off’.
…
- Do not leave the person alone; keep watching their breathing.
- If they are breathing but unconscious, place them safely on their side and follow the emergency operator's instructions.
- Do not make them vomit and do not give an unconscious person anything by mouth.
- Tell responders what and roughly how much they drank, and whether medicines or other substances may have been taken.
Shortcuts that do not work
Coffee, a cold shower and a walk do not speed up metabolism
Coffee can wake you up, but it does not sober you up
Caffeine may reduce sleepiness, but it does not remove alcohol from the blood. Feeling more alert does not mean coordination and judgement have returned.
Cold water does not reset the nervous system
A shower does not speed up the enzymes that break down alcohol, and for a severely intoxicated person it can increase the risk of injury and hypothermia.
How you feel is not a measurement
Tolerance and adrenaline can mask symptoms. Speaking clearly or ‘feeling fine’ says nothing definite about the result.
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Cheers lets you log every drink as you go and follow the estimated blood alcohol trend and forecast return to zero. This makes it easier to keep track of amount and pace instead of reconstructing the evening from memory. It supports more informed decisions — it is not a breathalyzer measurement or confirmation of sobriety.
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Sources
What this article is based on
- NIAAA: Understanding the Dangers of Alcohol Overdose
Warning signs of alcohol overdose, why BAC may continue to rise after drinking stops and what to do in an emergency.
- National Library of Medicine: Ethanol Toxicity — StatPearls
A clinical overview of symptoms commonly observed as blood alcohol concentration rises.
- SAMHSA / National Library of Medicine: Symptoms of Alcohol Intoxication
A table linking concentration ranges with clinical presentation, with an important warning about individual tolerance.
- World Health Organization: Alcohol — fact sheet
A global overview of alcohol's toxic and psychoactive effects and the factors that influence health risk.
