Alcohol poisoning overwhelms nearly every major system in your body at once, from suppressing the brainstem reflexes that keep you breathing to crashing your blood sugar and stripping your tissues of fluid. Unlike ordinary drunkenness, which the liver can process over several hours, alcohol poisoning occurs when ethanol floods the bloodstream faster than the body can break it down, and the cascade of damage it triggers goes far beyond feeling sick. What makes it especially dangerous is how many of these effects amplify each other: one failing system makes the next one worse.
How the Liver Gets Overwhelmed
Your liver handles the vast majority of alcohol breakdown, converting ethanol into acetaldehyde and then into harmless acetate through a series of enzyme-driven steps. But there is a hard ceiling on how fast this machinery works. The liver processes roughly one standard drink per hour, and when you blow past that rate, unmetabolized ethanol stays in circulation, reaching higher and higher concentrations in your blood and brain. The enzymes responsible for this process vary from person to person based on genetics, biological sex, and whether you have been drinking on an empty stomach.
Fasting makes a meaningful difference. In people who had not eaten, the so-called first-pass metabolism of ethanol (the amount broken down before it ever reaches general circulation) dropped substantially compared to fed individuals. In chronic heavy drinkers, this first-pass metabolism was already far lower than in non-drinkers, and fasting reduced it even further.1PubMed Central. Effects of fasting and chronic alcohol consumption on the first-pass metabolism of ethanol The practical upshot: drinking on an empty stomach or drinking heavily over time both mean more ethanol hits your bloodstream faster, pushing you closer to poisoning territory with fewer drinks than you might expect.
Breathing Slows Down, and the Airway Stops Protecting Itself
The most immediately life-threatening effect of alcohol poisoning is respiratory depression. Ethanol is a central nervous system depressant, and at high blood concentrations it suppresses the brainstem centers that regulate breathing. Breaths become shallow, irregular, or can stop entirely. A blood alcohol concentration above roughly 0.30 percent puts most people at serious risk for this kind of respiratory failure, and levels above 0.40 percent are frequently fatal.
Even before breathing stops outright, there is another airway threat: aspiration. When someone is deeply intoxicated and vomits, the normal reflexes that close off the windpipe and trigger coughing may not fire. A study of patients hospitalized with severe acute alcohol intoxication found that among those who had lost their protective reflexes, the aspiration rate was about 45 percent, compared to just 6 percent in patients whose reflexes remained intact.2PubMed. Aspiration risk in relation to Glasgow Coma Scale score and clinical parameters in patients with severe acute alcohol intoxication Vomit drawn into the lungs can cause aspiration pneumonia, chemical burns to lung tissue, or acute airway obstruction, and any of these can be fatal on their own.
This is why the advice to “let them sleep it off” can be deadly. A person passed out from alcohol poisoning may vomit without waking up. Placing an unconscious person on their side (the recovery position) helps, but it is not a substitute for emergency medical care when breathing is irregular or consciousness cannot be restored.
What Happens to the Heart and Blood Pressure
Alcohol causes blood vessels to relax and dilate, which drops blood pressure. In normal social drinking this effect is mild, but in poisoning-level intoxication the cardiovascular impact becomes dangerous. Research measuring blood pressure responses under simulated stress found that alcohol roughly doubled the drop in systolic blood pressure compared to placebo, and the normal reflex that constricts blood vessels to compensate for falling pressure was blunted. Forearm vascular resistance, the body’s main mechanism for stabilizing blood pressure when you stand up or shift position, essentially failed to kick in after alcohol intake.3PubMed Central. Alcohol potentiates orthostatic hypotension: implications for alcohol-related syncope
In practical terms, this means a severely intoxicated person who sits up, stands, or is moved can experience a sudden, steep blood pressure drop. The result is fainting, which by itself can cause head injuries from falling. When combined with a suppressed gag reflex and possible vomiting, loss of consciousness from a blood pressure crash compounds the aspiration risk described above. The heart itself may also develop irregular rhythms at very high blood alcohol levels, a phenomenon sometimes called “holiday heart” because it historically shows up after binge-drinking episodes.
Hypothermia From the Inside Out
Alcohol makes you feel warm because it dilates blood vessels near the skin, flushing heat to the surface. But that sensation is a trick: you are losing core body heat, not gaining it. In alcohol poisoning, this thermoregulatory breakdown becomes severe enough to cause hypothermia even in moderately cool environments, not just in freezing weather.
The mechanism behind this is worth understanding because it contradicts popular belief. While vasodilation does contribute to heat loss, research has found that the primary way alcohol drops core temperature during cold exposure is by impairing shivering. Alcohol-induced hypoglycemia (low blood sugar) robs muscles of the fuel they need to generate heat through shivering, which is the body’s main defense against cold.4Journal of Wilderness Medicine. Alcohol ingestion and temperature regulation during cold exposure So it is not just that the body is losing heat faster; it is also that the body cannot produce heat to replace what it is losing. A person who passes out drunk outdoors, or even on a cold floor indoors, can develop dangerous hypothermia in a timeframe that would be safe for a sober person.
Blood Sugar and the Metabolic Spiral
Alcohol disrupts the liver’s ability to release stored glucose into the bloodstream. Under normal circumstances, when blood sugar dips, the liver converts glycogen into glucose and pushes it out to keep levels stable. Ethanol metabolism hijacks the biochemical machinery needed for this process, and in someone who hasn’t eaten recently (when glycogen stores are already low), the result can be profound hypoglycemia. One study found that combining alcohol with glucose intake triggered hypoglycemia significantly more often than glucose alone.5PubMed Central. Combination of alcohol and glucose consumption as a risk to induce reactive hypoglycemia
Severe hypoglycemia produces confusion, seizures, loss of consciousness, and, in extreme cases, brain damage. These symptoms look a lot like the signs of alcohol poisoning itself, which makes low blood sugar dangerously easy to miss in someone who is already very drunk. Emergency departments routinely check glucose levels in patients with suspected alcohol poisoning for exactly this reason.
Beyond blood sugar, alcohol poisoning can tip the body’s acid-base balance into a condition called alcoholic ketoacidosis. When the liver is overwhelmed by alcohol and the body is running low on glucose, it starts burning fat for fuel in a way that produces acidic byproducts. This creates what clinicians call an anion gap metabolic acidosis, a state where the blood becomes abnormally acidic. In severe cases reviewed over a 24-year period, the lowest recorded blood pH was 6.8, far below the normal range of about 7.35 to 7.45, and the largest anion gap reached 57 mmol/L.6PubMed. Elevated osmol gaps in patients with alcoholic ketoacidosis Blood that acidic interferes with virtually every organ system, and correcting it requires intensive medical support.
Dehydration and Electrolyte Loss
Alcohol is a diuretic, meaning it causes your kidneys to produce more urine than the volume of fluid you are taking in. This happens because ethanol suppresses the release of vasopressin (also known as antidiuretic hormone) from the brain, and without vasopressin, the kidneys stop reclaiming water.7PubMed. Role of plasma vasopressin in changes of water balance accompanying acute alcohol intoxication In poisoning-level intoxication, especially when combined with vomiting, fluid losses can become substantial enough to cause clinically significant dehydration within hours.
Alongside water, the body dumps essential electrolytes: sodium, potassium, magnesium, and phosphate. These minerals regulate everything from nerve signaling to heart rhythm. When they drop too low, the risk of cardiac arrhythmias, muscle cramps, and seizures climbs. Electrolyte replacement is a cornerstone of emergency treatment for alcohol poisoning, and the dehydration itself compounds the blood pressure problems already described: less fluid in the system means less blood volume, which makes every positional blood pressure drop worse.
Damage to the Gut
Alcohol makes contact with every surface of the gastrointestinal tract on the way down, and at high concentrations it does real physical harm. In the stomach, ethanol disrupts the mucus barrier that protects the stomach lining and ramps up acid secretion, creating conditions for acute gastritis and erosions. It also impairs the coordinated muscle contractions that normally move food through the digestive system.8PubMed Central. Alcohol’s role in gastrointestinal tract disorders This disordered motility is part of why vomiting is so common in alcohol poisoning: the stomach is essentially in revolt.
Further along the tract, high ethanol concentrations can damage the lining of the small intestine, allowing bacterial toxins and other molecules to leak through into the bloodstream. This “leaky gut” effect triggers inflammation that can affect organs far from the gut itself, including the liver and the brain. In a single episode of extreme intoxication, the acute GI damage usually heals within days. But it contributes to the misery and the danger in real time, because each round of vomiting accelerates dehydration and electrolyte loss while raising the aspiration risk.
Muscle Breakdown and Kidney Injury
A lesser-known consequence of alcohol poisoning is rhabdomyolysis, the breakdown of skeletal muscle tissue. When someone is deeply unconscious from alcohol, they may lie in the same position for hours, compressing muscle groups and cutting off blood flow. Once blood flow returns, the damaged muscle fibers release their contents, including a protein called myoglobin, into the bloodstream. Case reports consistently show this pattern: a person drinks to the point of coma, lies immobilized for an extended period, and wakes up with dark urine and severe muscle pain.9PubMed Central. Nontraumatic rhabdomyolysis with short-term alcohol intoxication – a case report
The kidney damage that follows rhabdomyolysis can be severe. Myoglobin physically clogs the tiny tubules inside the kidneys that filter waste, and it is directly toxic to kidney cells. Combined with the dehydration and low blood pressure that alcohol poisoning also causes, this creates a perfect storm for acute kidney failure. The same case literature notes that beyond mechanical obstruction, renal vasoconstriction and the toxic effects of myoglobin on kidney tissue all contribute to the injury.9PubMed Central. Nontraumatic rhabdomyolysis with short-term alcohol intoxication – a case report In severe cases, dialysis is required until kidney function recovers, which can take weeks.
Effects on the Brain and Blood-Brain Barrier
At poisoning-level blood alcohol concentrations, ethanol suppresses activity across broad regions of the brain. The cerebellum, which coordinates movement and balance, is affected early, producing the stumbling and clumsiness associated with drunkenness. As concentrations climb, the hippocampus (involved in memory formation) effectively goes offline, producing blackouts. At the highest levels, the brainstem, which governs breathing, heart rate, and consciousness, becomes depressed enough to threaten life.
Alcohol also compromises the blood-brain barrier, the selective membrane that normally shields the brain from inflammatory molecules and pathogens circulating in the blood. Research has shown that alcohol exposure modulates circulating cytokines and other immune-signaling molecules that directly affect barrier integrity, potentially allowing substances into the brain that would normally be excluded.10PubMed Central. Alcohol, inflammation, and blood-brain barrier function in health and disease across development While this effect is studied most extensively in chronic drinkers, acute high-dose exposure also provokes a burst of neuroinflammation that may contribute to the prolonged cognitive fog some people experience even after blood alcohol drops to zero.
Why Some People Are More Vulnerable
Not everyone reaches alcohol poisoning at the same number of drinks. Biological sex is one of the biggest variables: women achieve higher blood alcohol concentrations than men even after drinking equivalent amounts adjusted for body weight, largely because women tend to have less total body water, which means ethanol is distributed through a smaller volume of fluid.11PubMed Central. Gender differences in moderate drinking effects The same number of drinks simply produces a higher concentration in the bloodstream.
Genetic variation in the enzymes that metabolize alcohol matters too. Certain variants of the genes encoding alcohol dehydrogenase and aldehyde dehydrogenase alter the speed at which ethanol is converted to acetaldehyde and then cleared. People carrying a variant of the ALDH2 gene that encodes a nearly inactive enzyme accumulate acetaldehyde rapidly, causing intense flushing, nausea, and racing heart even at low doses.12PubMed Central. The genetics of alcohol metabolism: role of alcohol dehydrogenase and aldehyde dehydrogenase variants Paradoxically, this is considered protective against heavy drinking and alcoholism because the reaction is so unpleasant, but people who push through it face a rapid toxic buildup that can escalate to poisoning faster than in someone who clears acetaldehyde efficiently.
Body size, age, food intake, medications, and chronic health conditions all shift the threshold as well. Adolescents and older adults are generally more susceptible. People with liver disease lose metabolic capacity. And as noted earlier, anyone who has been fasting enters the danger zone at a lower dose because their first-pass metabolism is reduced.
Mixing Alcohol With Other Depressants
Combining alcohol with opioids, benzodiazepines (drugs like Xanax or Valium), or both creates a synergistic effect on respiratory depression that is far more dangerous than any of these substances alone. Each one independently suppresses brainstem function; together, they can shut down breathing at doses that would be survivable individually. Research on the concurrent use of opioids, benzodiazepines, and alcohol has documented a clear increase in rates of overdose and death when these agents are combined.13PubMed Central. Risks, management, and monitoring of combination opioid, benzodiazepines, and/or alcohol use
Over-the-counter sleep aids, muscle relaxants, and certain antihistamines also have sedative properties that amplify alcohol’s depressant effects. Even prescription medications not typically thought of as sedatives, such as gabapentin, can compound the risk. The takeaway is straightforward: anything else that slows the central nervous system makes alcohol poisoning more likely and more dangerous at a lower dose of alcohol.
Recognizing Alcohol Poisoning in Someone Else
The distinction between “very drunk” and “alcohol poisoning” is not always obvious, and erring on the side of caution saves lives. Signs that should prompt a call to emergency services include:
- Unconsciousness: the person cannot be woken by shaking or shouting.
- Irregular breathing: gaps of more than 10 seconds between breaths, or fewer than about 8 breaths per minute.
- Seizures: convulsions with or without preceding warning signs.
- Skin changes: pale, bluish, or cold and clammy skin, especially around the lips and fingertips.
- Vomiting while unconscious: particularly if the person is on their back.
Blood alcohol can continue to rise for 30 to 90 minutes after the last drink, because alcohol in the stomach and intestines keeps absorbing into the bloodstream. A person who seemed coherent when they stopped drinking can deteriorate significantly in the following hour. Do not assume the worst has passed just because the bottle is down. If in doubt, call for help and keep the person on their side while waiting.
Genetic Variants and “Alcohol Flush”
The ALDH2 deficiency mentioned earlier is especially common in people of East Asian descent, affecting an estimated 30 to 40 percent of that population. People with this variant experience a dramatic flush reaction: red face and neck, nausea, rapid heartbeat, and headache after even a small amount of alcohol. The reaction is caused by a buildup of acetaldehyde, a toxic intermediate product of alcohol metabolism, that the deficient enzyme cannot clear efficiently.12PubMed Central. The genetics of alcohol metabolism: role of alcohol dehydrogenase and aldehyde dehydrogenase variants
What is less widely known is that acetaldehyde itself is a carcinogen, and people with the ALDH2 deficiency who drink regularly have elevated rates of esophageal cancer and other GI cancers compared to people who clear acetaldehyde normally. In the context of acute poisoning, the acetaldehyde accumulation intensifies nausea and cardiovascular stress, adding another toxic layer on top of the ethanol-driven damage. The flush is not just an embarrassment or inconvenience; it is a visible sign that a harmful substance is accumulating faster than the body can handle it.