You're Sensitive to Alcohol. Your Genes Explain Why.

ADH1B is the gatekeeper enzyme. It takes pure ethanol (the alcohol you drink) and converts it into acetaldehyde, a toxic intermediate. This is the first critical step. In people with the common, slower version of this gene, this conversion happens at a normal pace. But the Arg48His variant, found in roughly 20% of people with European ancestry and up to 70% of people with East Asian ancestry, codes for a faster-acting enzyme.

If you carry the Arg/Arg variant, your body converts ethanol to acetaldehyde very rapidly. That sounds like it might be good, but here’s the problem: you’re flooding your system with acetaldehyde faster than the next enzyme in the chain can clear it away. The acetaldehyde backs up, and that’s when you feel it: flushing in your face and neck, nausea, heart palpitations, sometimes a spinning sensation.

You might notice these symptoms kick in after just one or two drinks, even though you’re not actually drunk yet. Your friends are still feeling relaxed while you’re dealing with the physiological cascade of acetaldehyde buildup. Some people with fast ADH1B describe it as hitting a wall: one drink feels fine, two drinks feel manageable, and then suddenly you’re flushed, dizzy, and done for the night.

ALDH2 is the enzyme that converts acetaldehyde (toxic) into acetic acid (harmless). This is the final step in alcohol metabolism, and it’s absolutely critical. Your body needs ALDH2 to be functioning well to prevent acetaldehyde from building up to dangerous levels.

The Glu487Lys variant, particularly the *2 allele, is found in approximately 35 to 40% of people with East Asian ancestry and is rare in European ancestry. This variant nearly eliminates ALDH2 function. If you carry even one copy of the *2 allele, you have dramatically reduced capacity to clear acetaldehyde. If you carry two copies, you have almost no ALDH2 activity at all.

When ALDH2 is impaired, acetaldehyde accumulates even from small amounts of alcohol. You might experience severe facial flushing, intense nausea, vomiting, chest pain, or severe headache after just half a drink. Some people with this variant have tried drinking despite the symptoms, thinking they might build tolerance. They don’t. The symptoms persist or worsen because the problem isn’t tolerance; it’s a complete lack of the enzyme needed to clear the toxin.

While ADH and ALDH are the primary alcohol metabolism pathway, your body has a backup route: CYP2E1. This enzyme in your liver can metabolize alcohol, but it does something the primary pathway doesn’t: it generates oxidative stress and reactive oxygen species (ROS) as a byproduct. Think of it as a less efficient conversion that leaves toxic residue.

CYP2E1 variants don’t change whether you get drunk or how quickly, but they do determine how much oxidative damage your liver incurs from alcohol exposure. People with certain CYP2E1 variants generate significantly more oxidative stress per drink, leading to faster liver damage and higher cancer risk from chronic alcohol use. Prevalence varies by population, and some variants are fairly common.

You might not feel the effects of oxidative stress immediately the way you feel acetaldehyde buildup. But over time, repeated alcohol exposure with a higher-stress CYP2E1 variant increases your risk of liver inflammation, fatty liver disease, and cirrhosis. You might notice fatigue after drinking, slower recovery between hangover symptoms, or a general sense that alcohol is just harder on your body than it is for others.

GSTM1 is a detoxification enzyme that clears acetaldehyde and other toxic metabolites from your cells. It’s part of your body’s general cleanup crew. Roughly 50% of the population carries a GSTM1 null genotype, meaning they have a complete deletion of this gene and produce no functional GSTM1 enzyme.

If you’re in that 50% with the null variant, your body has lost a significant detoxification pathway, which means acetaldehyde lingers longer and contributes more heavily to hangover symptoms and overall alcohol-related damage. This doesn’t prevent you from metabolizing alcohol, but it does mean the toxic intermediate stays around longer while your remaining enzymes work to clear it.

You’ll notice this most acutely in how severe your hangovers are relative to how much you drank. Two drinks might leave you with a headache, nausea, and brain fog that lasts into the next afternoon. Your friends with two functional GSTM1 alleles recover by morning. The difference isn’t willpower or hydration; it’s the presence or absence of this detox enzyme.

COMT clears dopamine and norepinephrine from your brain and nervous system. Alcohol disrupts these neurotransmitter systems, and how quickly COMT can restore balance determines how you experience alcohol’s mood and behavioral effects.

The Val158Met variant is common, with roughly 25% of people with European ancestry carrying two copies of the slow variant (Met/Met). If you carry the slow COMT variant, your brain clears stress hormones more slowly, which means alcohol’s dopamine spike followed by its crash creates a more dramatic emotional rollercoaster. This can show up as heightened impulsivity while drinking, emotional sensitivity or mood swings, or more severe low mood the next day.

You might notice that alcohol makes you more talkative, reckless, or emotionally reactive than your peers. Or that after drinking, you crash hard: low mood, social anxiety, or irritability the next day even if you didn’t drink that much. This isn’t a character flaw. Your brain is slower at clearing the neurochemical aftermath of alcohol’s effects on your dopamine system.

SLC6A4 codes for the serotonin transporter, the protein that recycles serotonin back into neurons. Alcohol interferes with serotonin signaling, and how well your serotonin transporter can restore balance determines your mood recovery after drinking.

The 5-HTTLPR short allele is carried by roughly 40% of the population. If you carry at least one copy of the short allele, your serotonin reuptake is less efficient, which means alcohol’s disruption to serotonin creates more pronounced mood effects: heightened anxiety while drinking, or significant anxiety and mood dips the next day. Some people describe it as feeling emotionally fragile or socially anxious after drinking, even from relatively small amounts.

You might be the person who gets quiet or withdrawn after a drink or two, or who feels sad or anxious the next day disproportionate to how much you drank. Your friends feel fine; you feel emotionally depleted. This often gets attributed to ‘alcohol making you sad’ when really it’s your SLC6A4 variant making serotonin recovery slower after alcohol disrupts it.