Alcohol generally makes pupils a little wider rather than smaller.1PubMed Central. Illicit drugs: Effects on eye The widening is modest, though, and pupils change size all day for reasons that have nothing to do with drink. The more revealing eye changes are in how the eyes move and respond, not in how big the pupils look.
How Much Alcohol Widens the Pupils
In older adults given alcohol, pupils grew about 17.5% wider soon after drinking, compared with about 8.6% after a placebo drink.2PubMed Central. The eyes have it: Alcohol‐induced eye movement impairment and perceived impairment in older adults with and without alcohol use disorder Later in the session the gap shrank to about 18% versus 14% and no longer clearly differed.3PubMed Central. The eyes have it: Alcohol‐induced eye movement impairment and perceived impairment in older adults with and without alcohol use disorder People with and without a drinking problem showed the same pupil change.4PubMed Central. The eyes have it: Alcohol‐induced eye movement impairment and perceived impairment in older adults with and without alcohol use disorder
Pupils also widen for reasons that have nothing to do with alcohol. Dim bars and evening light open them on their own, and excitement, attention, and emotion do the same within seconds. That is why the placebo drinkers’ pupils grew too.
The dose matters. Pupils widened noticeably in people who reached higher breath alcohol levels.5PubMed Central. Retinal-Image Quality and Night-Vision Performance after Alcohol Consumption In drivers given alcohol, pupil width also rose clearly.6PubMed Central. Deterioration of binocular vision after alcohol intake influences driving performance But people with breath alcohol under 0.25 mg/L, about the UK drink-drive limit, showed no clear change.7PubMed Central. Retinal-Image Quality and Night-Vision Performance after Alcohol Consumption
Even when the change is there, it is small. In one group the average widening was smaller than 0.5 mm, below what the measuring device could reliably detect.8PubMed Central. A visual test based on a freeware software for quantifying and displaying night-vision disturbances: study in subjects after alcohol consumption To the naked eye across a table, the difference usually can’t be seen. The only fair comparison is the same person in the same light.
Why Some Sources Say Alcohol Makes Pupils Smaller
Some treatment-centre sites argue that because alcohol depresses the nervous system, the “rest” side of it may take over and shrink pupils.9High Focus Centers. Does Alcohol Make Your Pupils Small? Understanding the Effects of Alcohol on Pupil Size The reasoning sounds sensible, but alcohol affects both branches of the nervous system that steer pupil size, and which one wins can depend on dose, light, and the person. Direct measurement is a stronger guide than reasoning from mechanism, and controlled studies of people drinking consistently found wider pupils, not smaller ones.10PubMed Central. The eyes have it: Alcohol‐induced eye movement impairment and perceived impairment in older adults with and without alcohol use disorder11PubMed Central. Deterioration of binocular vision after alcohol intake influences driving performance12PubMed Central. Retinal-Image Quality and Night-Vision Performance after Alcohol Consumption13PubMed Central. Changes in Visual Performance under the Effects of Moderate–High Alcohol Consumption: The Influence of Biological Sex
Pinpoint pupils are a classic sign of opioids such as heroin, oxycodone, or fentanyl. Very small pupils in someone who seems drunk can therefore mean another substance is involved. Heavy drowsiness plus pinpoint pupils and slow breathing is an emergency, so call emergency services.
Slower Reactions to Light
Drinking changes how pupils respond as well as how big they are. Short-term drinking is linked to slower pupil reactions to light.14PubMed Central. Illicit drugs: Effects on eye Bright glare also takes noticeably longer to recover from after alcohol.15PubMed. Marijuana, alcohol, and combined drug effects on the time course of glare recovery Wider pupils let in more stray light, adding to the dazzle. Oncoming headlights can leave a drinker dazzled longer, which is one reason night driving after drinking is especially risky.
In a sober person, a pupil shrinks within a fraction of a second when a bright light hits the eye. An impaired pupil may shrink more lazily, or drift back wider while the light is still on it. Seeing this takes a penlight and a fairly dark room, not a glance across a table.
Simple timing isn’t a dependable test either. In one workplace study, reaction timing after alcohol differed from normal by only a few thousandths of a second.16PubMed Central. The pupillary light reflex (PLR) as a marker for the ability to work or drive – a feasibility study Sleep loss pushed the timing the other way.17PubMed Central. The pupillary light reflex (PLR) as a marker for the ability to work or drive – a feasibility study
Pupil changes can also appear after drinking stops: during alcohol withdrawal, pupils respond to light more slowly and constrict less briskly.18PubMed Central. Eyeing up the Future of the Pupillary Light Reflex in Neurodiagnostics
Can You Tell Someone Is Drunk From Their Eyes
Pupil size is a poor test. Pupil response was tested as a way to spot drivers between 0.04% and 0.08% and did not work.19PubMed. Sobriety tests for low blood alcohol concentrations Differences between people were far larger than the change drinking caused in any one person.20PubMed. Sobriety tests for low blood alcohol concentrations
Eye jerking is the telling sign. Alcohol causes nystagmus, a jerking of the eyes as they look to the side.21PubMed Central. Illicit drugs: Effects on eye This gaze test was the only reliable eye-based measure of low blood alcohol in testing.22PubMed. Sobriety tests for low blood alcohol concentrations That is why police field sobriety tests use it rather than pupil size. At very high levels, above about 0.15%, the jerking gets stronger and eyes may struggle to stay open.23Canadian Centre for Addictions. What Do Drug Eyes Look Like and What They Tell You
At the roadside, the officer holds a pen or small light and moves it slowly to one side and then the other while the person follows it with their eyes only, keeping the head still. They watch whether the eyes track smoothly or jerk. Jerking that begins before the eyes reach the side counts as a sign against the person. It is one part of a set of checks that also includes balance and walking tasks, not a verdict on its own.
If you are looking at a friend, glassy or red eyes and droopy eyelids are common, though none of these alone proves how much someone has had. Slurred speech and unsteady walking are usually clearer clues than anything in the pupils. Confusion, repeated vomiting, or trouble staying awake are danger signs and should not be waved off as just being drunk.
Do not leave them to sleep on their back, where they could choke on vomit; lay them on their side and stay with them. If their breathing slows or becomes irregular, or you cannot wake them, call emergency services.
Other Ways Alcohol Affects Eyes and Vision
Wider pupils let in more light at the edges of the lens, which adds blur and halos around lights.24PubMed Central. A visual test based on a freeware software for quantifying and displaying night-vision disturbances: study in subjects after alcohol consumption After moderate to heavy drinking, people saw more halos in both eyes.25PubMed Central. Changes in Visual Performance under the Effects of Moderate–High Alcohol Consumption: The Influence of Biological Sex Drinking can also cause double vision and weaker contrast seeing.26PubMed Central. Illicit drugs: Effects on eye
Double vision happens because the two eyes stop aiming together precisely, so each sends a slightly different picture to the brain. Closing one eye to cope does not make driving safe.
Alcohol often leaves eyes red and bloodshot, and heavy drinking can trigger eyelid twitching.27PubMed Central. Illicit drugs: Effects on eye These usually fade as the alcohol wears off.
Halos around lights that appear while drinking and clear by morning are an expected effect of the alcohol. Halos that keep appearing when you are sober deserve an eye check, since they can have other causes. Sudden loss of vision, or a painful red eye, needs prompt medical care and should not be put down to drinking. Ordinary drink-related redness is usually painless, which helps separate it from a problem.
Alcohol Mixed With Cannabis or Other Drugs
Alcohol and marijuana together produced no change in pupil size.28PubMed. Pupil size after use of marijuana and alcohol Yet higher THC in the blood was tied to red eyes, wider pupils, and slower light reactions.29PubMed. Impairment due to cannabis and ethanol: clinical signs and additive effects Both drugs, alone or combined, slowed glare recovery.30PubMed. Marijuana, alcohol, and combined drug effects on the time course of glare recovery Normal-looking pupils don’t rule out impairment from a mix.
Stimulants such as cocaine widen pupils strongly, which can push them well beyond what alcohol alone does. Opioids shrink pupils to pinpoints, pulling them the opposite way. A mix of substances can produce almost any pupil size, including one that looks normal. Judge by behaviour, breathing and alertness instead, and treat slow breathing or being hard to wake as an emergency.
Eyes and Long-Term Drinking
People with alcohol dependence show different pupil responses to light and darkness than non-drinkers, even at rest.31PubMed. Pupillometric studies of alcoholism People recently sober showed larger pupil widening to pictures of all kinds.32Oxford Academic. Overactivation of the Pupillary Response to Emotional Information in Short- and Long-Term Alcohol Abstinent Patients But people sober for a long time responded like non-drinkers, and responses settled the longer they’d abstained.33Oxford Academic. Overactivation of the Pupillary Response to Emotional Information in Short- and Long-Term Alcohol Abstinent Patients
Cravings may show in the eyes too. In early research, people in treatment whose pupils widened more at alcohol images were more likely to relapse.34PubMed Central. Pupillary reactivity to alcohol cues as a predictive biomarker of alcohol relapse following treatment in a pilot study Stopping heavy drinking suddenly can be dangerous, with withdrawal that can bring seizures, so a doctor can help plan a safe withdrawal after heavy or long-term use.