How to Tell if Someone Is Drunk — The Observable Signs and When to Act

The Spectrum of Intoxication

Intoxication isn't binary — drunk or not drunk. It's a spectrum that runs from mild loosening-up to dangerous physiological impairment, and the signs at different points on that spectrum are qualitatively different. The practical challenge is that people with high tolerance can appear far less intoxicated than their blood alcohol level warrants, while people with low tolerance or certain medications can appear extremely impaired at relatively low BAC. Behavioural observation is useful, but it's not perfectly correlated with BAC, and understanding the full picture reduces the risk of misreading dangerous situations as merely social ones.

Mild Intoxication (approximately 0.03–0.07% BAC)

At mild intoxication levels, the changes are largely positive in character — which is why alcohol is popular. The person is more talkative and sociable than usual. Self-consciousness is reduced. They're quicker to laugh, more likely to approach people they don't know, more willing to share opinions or feelings they'd normally keep to themselves.

Observable indicators: slightly louder than usual, more animated facial expressions, slightly increased reaction time that they probably don't notice, mildly flushed skin in those susceptible to alcohol flushing. Decision-making and coordination are mostly unaffected at this level, though risk assessment is already subtly impaired — the person is slightly more likely to make decisions they'd reconsider sober.

Moderate Intoxication (approximately 0.07–0.15% BAC)

Moderate intoxication is where the impairments become visible and safety-relevant. This is also the range in which many people describe themselves as "just having a few drinks" — the level where social drinking often sits.

Observable indicators: slurred speech (the muscles controlling articulation are affected, producing thickened consonants and slower speech rhythm); impaired coordination visible in fine motor tasks (difficulty with small objects, unsteady pouring); reduced balance and reaction time; increased emotional variability (both positive and negative — elation flips more easily to irritation or tears than when sober); and the beginning of short-term memory impairment that may produce patchy recall of events.

At this level, the person is legally impaired for driving in virtually all jurisdictions. They are also a poor judge of their own impairment — a well-documented feature of alcohol intoxication is that self-assessment of impairment decreases as actual impairment increases.

Significant Intoxication (approximately 0.15–0.25% BAC)

Significant intoxication produces clearly observable impairment across multiple domains. The person's speech is noticeably slurred and difficult to follow. Their coordination is visibly compromised — they may stumble or need to hold onto furniture. Emotional control is substantially reduced, producing exaggerated responses, increased likelihood of conflict, and lowered inhibition on impulsive behaviour. Nausea and vomiting are common in this range. Memory encoding is significantly impaired; events from this portion of the evening are unlikely to be recalled clearly.

At this level, the person needs to be monitored rather than left alone. Their judgement about their own safety, about whether to continue drinking, and about consent in any situation requiring it is substantially impaired. The social responsibility of people around them increases significantly.

Severe Intoxication and Transition to Danger (0.25% and above)

At BAC levels above 0.25%, the signs transition from "seriously drunk" to potentially dangerous. Consciousness is impaired — the person may be confused about where they are or who they're with. They may alternate between being semi-conscious and unconscious. They are completely unable to manage themselves safely. Breathing may become slower and more irregular. The gag reflex is compromised.

This is the threshold at which responsible bystander behaviour requires action, not just observation. The recovery position, monitoring of breathing, and calling emergency services if breathing becomes irregular or the person cannot be roused are the appropriate responses. The signals that specifically indicate medical emergency are covered in the alcohol poisoning article in this hub.

High Tolerance: When the Appearance Doesn't Match the Risk

People with high alcohol tolerance — regular heavy drinkers — may appear only moderately affected at BAC levels that would incapacitate a non-tolerant person. This creates a specific danger: the person appears "fine" by behavioural observation but their actual blood alcohol concentration is at a level where physiological risk is significant. Their brainstem functions are suppressed to a degree their behaviour doesn't reflect, because the brain has adapted to appear functional at higher BAC.

If someone with known heavy drinking history appears much more drunk than usual despite drinking what seems to be their normal amount, this is worth taking seriously — it may indicate illness, interaction with medication, or an unusually high-volume session. The baseline of "how they normally look when drunk" is not a reliable safety indicator when that baseline involves tolerance to dangerous BAC levels.