Alcohol poisoning is a life-threatening emergency marked by unconsciousness, dangerously slow breathing, and the real possibility of death, while a hangover is the familiar misery of headache, nausea, and fatigue that sets in the morning after heavy drinking. The two conditions share a common cause but sit on completely different levels of medical seriousness. Confusing one for the other can be fatal, because a person in the early stages of alcohol poisoning can look like someone who just had too much to drink and needs to “sleep it off.” Understanding the specific symptoms of each is what separates a bad morning from a 911 call.
What Alcohol Poisoning Actually Looks Like
Alcohol poisoning happens when blood alcohol concentration climbs high enough to start shutting down basic bodily functions. At blood alcohol levels around 0.30 to 0.40 percent, most people become incapacitated or unconscious, with slow and shallow breathing, and face a real risk of death from paralysis of the respiratory centers in the brainstem.1WIREs Forensic Science. Alcohol, its analysis in blood and breath for forensic purposes, impairment effects, and acute toxicity That is roughly four to five times the legal driving limit in most places. The person does not have to drink a specific amount to reach that threshold; body size, tolerance, speed of drinking, food intake, and whether other substances are involved all play a role.
The symptoms of alcohol poisoning unfold while the person is still intoxicated, not the next morning. They include:
- Unconsciousness or stupor: The person cannot be woken up, or can only be briefly roused before losing consciousness again.
- Slow or irregular breathing: Fewer than eight breaths per minute, or gaps of ten seconds or more between breaths.
- Vomiting while unconscious: This creates a choking risk because protective reflexes like the gag reflex are suppressed.
- Seizures: Caused by severe drops in blood sugar or electrolyte disruption.
- Hypothermia: The skin may feel cold and clammy, and the person’s body temperature drops because alcohol dilates blood vessels near the skin surface.
- Blue-tinged or pale skin: Especially around the lips and fingertips, signaling that the body is not getting enough oxygen.
The dangerous thing about alcohol poisoning is that blood alcohol can keep rising even after the person stops drinking, because alcohol in the stomach and intestines continues to be absorbed. Someone who seems “just very drunk” at midnight can be in respiratory failure by 1 a.m. if the alcohol already consumed is still entering the bloodstream.
What a Hangover Feels Like
A hangover shows up after blood alcohol has dropped back toward zero, typically peaking the morning after a heavy drinking session. Research has found a direct relationship between peak blood alcohol concentration and hangover severity.2PubMed Central. The Role of Alcohol Metabolism in the Pathology of Alcohol Hangover The higher you got, the worse you tend to feel. But unlike alcohol poisoning, a hangover is not immediately dangerous. It is deeply unpleasant, but it resolves on its own.
Common hangover symptoms include headache, nausea and sometimes vomiting, sensitivity to light and sound, fatigue, muscle aches, dizziness, thirst, irritability, and difficulty concentrating. Most people are familiar with this list from personal experience. What makes the hangover distinct from poisoning is timing and consciousness: you are awake, you are aware of how terrible you feel, and your breathing and heart rate are normal even though your body feels wrecked.
Researchers have identified multiple contributors to the hangover state. Alcohol promotes increased urine output, disrupts the gastrointestinal tract, affects blood sugar concentrations, and disturbs sleep patterns and biological rhythms.3PubMed Central. Alcohol hangover: mechanisms and mediators On top of all that, there appears to be a mild withdrawal component: the brain adapts to the presence of alcohol during a drinking session and then has to readjust when it is gone.
The Critical Difference You Need to Recognize
The single most important distinction is whether the person is conscious and responsive. A hungover person groans about their headache, shuffles to the bathroom, and generally looks miserable but functional. A person with alcohol poisoning cannot do any of those things. They may be limp, unresponsive, breathing irregularly, or vomiting without waking up.
Timing matters too. Alcohol poisoning happens during or shortly after drinking, while blood alcohol is still dangerously high. A hangover happens hours later, after the body has metabolized most of the alcohol. If someone passes out at a party and cannot be woken, that is not a hangover in progress. That is a potential poisoning, and waiting until morning to see if they feel better can be a lethal mistake.
There is a gray zone that trips people up: the heavily intoxicated person who is conscious but slurring, stumbling, and vomiting. That person is not yet in alcohol poisoning territory in most cases, but they could get there quickly if they keep drinking or if the alcohol already consumed is still being absorbed. The shift from severe intoxication to poisoning is not always dramatic. Breathing can slow gradually, and consciousness can fade without anyone noticing in a loud or dark environment.
When to Call Emergency Services
You should call for emergency help any time someone who has been drinking shows these signs: they cannot be woken up, their breathing is slow or irregular, they are vomiting while unconscious, their skin is blue or pale, or they are having seizures. Do not wait for all of these to appear. Even one is enough to warrant a call.
A common and dangerous mistake is assuming the person just needs to “sleep it off.” Laying an unconscious drunk person on their back and leaving them alone is how aspiration deaths happen: they vomit and choke without the ability to clear their airway. If you are with someone who is unconscious and you are waiting for help, turn them on their side in a recovery position so that any vomit can drain out of the mouth rather than into the lungs.
Research on how bystanders respond to alcohol intoxication suggests that when people around an intoxicated person offer to provide care, the person is less likely to be transported to a hospital, which could reflect either effective monitoring or a false sense of security.4Journal of Collegiate Emergency Medical Services. Assessment of Bystander Intervention on EMS Transport Decisions for Cases of Alcohol Intoxication at a Small College in New York State The takeaway is that “my friend is watching them” is not a substitute for medical evaluation when warning signs are present. Untrained bystanders cannot monitor breathing rate or oxygen levels the way medical professionals can.
What Is Actually Happening in Your Body During a Hangover
For years, the standard explanation for hangovers was simple dehydration: alcohol makes you urinate more, you lose fluids, and that causes the headache and fatigue. Dehydration is part of the picture, but recent research suggests the bigger driver is inflammation. A growing body of evidence frames the hangover as a form of sickness behavior triggered by an inflammatory response to alcohol.5PubMed. Inflammation, oxidative stress and gut microbiome perturbation: A narrative review of mechanisms and treatment of the alcohol hangover In other words, the hangover is your immune system responding to what alcohol did to your body, much the way you feel achy and foggy when you are fighting off an infection.
Studies have found that after heavy drinking, markers of immune activation spike. Concentrations of inflammatory signaling molecules like IL-6 and IL-10 increased significantly in saliva the day after heavy alcohol consumption.6PubMed Central. Immune Responses after Heavy Alcohol Consumption: Cytokine Concentrations in Hangover-Sensitive and Hangover-Resistant Drinkers This immune response helps explain why hangover symptoms feel so much like being sick: the fatigue, the brain fog, the loss of appetite, and the general sense that your body wants you to stay in bed.
On top of inflammation, a review of the evidence identified hormonal alterations, disrupted cytokine pathways, and the direct toxic effects of alcohol and its breakdown products as contributing factors.7PubMed. The alcohol hangover The heart works harder during a hangover despite normal blood vessel resistance, and brain-wave recordings show a diffuse slowing pattern. None of this is life-threatening in isolation, but it adds up to the overall feeling of being physically and mentally wrecked.
Why Water Does Not Fix a Hangover
One of the most persistent pieces of folk wisdom is that drinking water during or after alcohol will prevent or cure a hangover. Recent research paints a more skeptical picture. Survey data showed that water consumption during or directly after alcohol had only a modest effect in preventing the next-day hangover, and the amount of water consumed the next morning was unrelated to changes in hangover severity or thirst.8PubMed. Alcohol hangover versus dehydration revisited: The effect of drinking water to prevent or alleviate the alcohol hangover The data suggest that dehydration and hangover are two things that happen at the same time after drinking, but one does not cause the other as much as people assume. Fixing the dehydration helps with thirst and dry mouth but does not meaningfully reduce the headache, nausea, or fatigue.
That said, rehydration is not useless. A review in a major medical journal listed rehydration alongside prostaglandin inhibitors (common over-the-counter anti-inflammatory painkillers like ibuprofen) and vitamin B6 as interventions with some evidence of effectiveness.7PubMed. The alcohol hangover The point is not to skip water but to recognize that water alone is an incomplete remedy. If inflammation is the main driver of hangover symptoms, it makes sense that anti-inflammatory medications would help more than hydration on its own.
Why Some People Get Worse Hangovers Than Others
If you have ever watched someone drink the same amount as you and wake up feeling fine while you are incapacitated, genetics are a likely explanation. One well-studied factor is variation in the gene for aldehyde dehydrogenase, the enzyme that breaks down a toxic byproduct of alcohol metabolism. People of East Asian descent who carry a less active version of this enzyme tend to experience more severe hangovers.9PubMed. Hangover symptoms in Asian Americans with variations in the aldehyde dehydrogenase (ALDH2) gene Research in Japanese workers confirmed that having the less active form, along with the visible alcohol flushing reaction, was positively associated with hangover susceptibility.10PubMed. Hangover susceptibility in relation to aldehyde dehydrogenase-2 genotype, alcohol flushing, and mean corpuscular volume in Japanese workers The mechanism links back to acetaldehyde, a toxic intermediate that accumulates when the enzyme cannot break it down efficiently. Interestingly, while acetaldehyde appears connected to hangover susceptibility through genetics, population-level studies have not found a strong direct correlation between acetaldehyde blood levels and hangover severity across all drinkers.2PubMed Central. The Role of Alcohol Metabolism in the Pathology of Alcohol Hangover
Genetics aside, what you drink also matters. A controlled study comparing bourbon and vodka at the same total alcohol dose found that hangover ratings were higher after bourbon than vodka.11PubMed Central. Intoxication with Bourbon versus Vodka: Effects on Hangover, Sleep and Next-Day Neurocognitive Performance in Young Adults The difference is attributed to congeners, which are biologically active compounds produced during fermentation and aging. Darker spirits like bourbon, brandy, and red wine tend to have higher congener concentrations than lighter spirits like vodka and gin. This does not mean switching to vodka will prevent hangovers entirely, since the alcohol itself is still the primary culprit. But it can move the needle on severity.
Other factors that influence hangover susceptibility include personality traits, family history of alcohol problems, use of other drugs alongside alcohol, and individual variation in how the immune system responds to alcohol’s inflammatory effects. Some people are simply “hangover resistant” and others are “hangover sensitive,” and these categories appear to correspond to different immune profiles after drinking.
The Hangover’s Effect on Your Brain the Next Day
One underappreciated aspect of hangovers is their effect on cognitive performance. People often assume they are fine to drive or work the morning after heavy drinking because they are no longer drunk, but a systematic review and meta-analysis found measurable impairments in short-term memory, long-term memory, sustained attention, and psychomotor speed during hangover.12PubMed Central. A systematic review of the next‐day effects of heavy alcohol consumption on cognitive performance Driving ability was also impaired. These are not subtle effects: the review found moderate-to-large effect sizes across studies, meaning the cognitive impact is comparable to being mildly intoxicated even when blood alcohol has returned to zero.
Sleep disruption plays a role here. Research has shown that alcohol negatively affects sleep quality, and that poor sleep during a drinking night is related to both worse hangover severity and worse cognitive performance the next day. The duration of nighttime awakenings was negatively associated with multiple individual hangover symptoms, and overall hangover severity accounted for a meaningful amount of the variance in how long people took to complete a cognitive task.13PubMed Central. The Relationship between Alcohol Hangover Severity, Sleep and Cognitive Performance; a Naturalistic Study In practical terms, you may have gotten eight hours of sleep, but your body spent a good portion of that time metabolizing alcohol rather than cycling through normal restorative sleep stages. The result is fatigue and mental sluggishness that hydration and caffeine cannot fully compensate for.
What Alcohol Does to Your Gut
The nausea, stomach pain, and sometimes diarrhea that accompany heavy drinking are not just side effects of dehydration or general inflammation. Alcohol has direct effects on the gastrointestinal tract. It promotes the development of superficial gastritis, which is irritation and inflammation of the stomach lining.14PubMed Central. The effects of alcohol consumption upon the gastrointestinal tract This is why the morning-after nausea from a hangover feels distinctly stomach-centered rather than like the generalized queasiness of motion sickness. Alcohol also increases acid production, relaxes the valve between the stomach and esophagus (leading to reflux), and speeds up or slows down intestinal motility depending on the amount consumed.
For people who drink heavily on a regular basis, this can progress to chronic atrophic gastritis, a more serious long-term change to the stomach lining. But even a single episode of binge drinking is enough to inflame the stomach lining for a day or two, which is part of why eating feels so unappealing during a hangover.
Blood sugar also deserves a mention. Alcohol interferes with the liver’s ability to release glucose, and when combined with carbohydrate-heavy mixers or foods, the result can be a reactive blood sugar drop. Research has found that alcohol combined with glucose consumption was significantly more likely to trigger reactive hypoglycemia than glucose alone.15PubMed Central. Combination of alcohol and glucose consumption as a risk to induce reactive hypoglycemia Low blood sugar during or after drinking can contribute to shakiness, weakness, sweating, and difficulty concentrating, symptoms that overlap heavily with both hangovers and, at the extreme end, with alcohol poisoning. For people with diabetes or other metabolic conditions, the blood sugar effects of heavy drinking carry additional risk.
The Flushing Response and What It Tells You
If your face turns red and hot after even a small amount of alcohol, that visible reaction is likely related to the same enzyme variation discussed above. The alcohol flushing response occurs when acetaldehyde accumulates because the body lacks fully functional aldehyde dehydrogenase. Studies have linked this flushing to both increased hangover susceptibility and, paradoxically, some degree of protection against developing heavy drinking habits, because the unpleasant reaction discourages continued consumption.9PubMed. Hangover symptoms in Asian Americans with variations in the aldehyde dehydrogenase (ALDH2) gene
People who flush after drinking and push through the discomfort anyway are accumulating more acetaldehyde than those who do not flush, which is associated with elevated cancer risk over time. The flush is not a harmless cosmetic reaction; it is a visible signal that the body is struggling with a specific step of alcohol metabolism. For someone who flushes, even moderate drinking produces a biochemical environment that most non-flushers only experience at much higher doses. This does not mean non-flushers are immune to hangover or to the long-term effects of alcohol, but flushing is a reliable early warning that the body’s detoxification machinery is working under strain.