One Drink Leaves You Wrecked. Your Genes May Explain Why.

ADH1B is the enzyme that takes the alcohol you drink (ethanol) and converts it into acetaldehyde. Acetaldehyde is the toxic compound responsible for most of a hangover’s miserable symptoms: flushing, nausea, headache, and that pounding heartbeat. Your body needs to convert acetaldehyde into harmless acetate as quickly as possible. If this first step is slow, acetaldehyde builds up. If it’s fast, you produce a lot of acetaldehyde very quickly, and now your second enzyme (ALDH2) has to work overtime to clear it.

The ADH1B Arg48His variant affects how fast you convert ethanol to acetaldehyde. The Arg/Arg genotype, carried by roughly 20% of people with European ancestry and up to 70% of people with East Asian ancestry, makes you a fast converter. Fast converters produce acetaldehyde quickly, which means you feel the effects of alcohol faster and more intensely, even at small doses.

If you’re an ADH1B fast converter, you might notice that one drink hits you noticeably harder than it does your friends. You might flush within minutes. Your heart might race. You might feel dizzy or nauseous before you’ve even finished the drink. It’s not because you’re not eating enough or because you’re anxious. Your liver is doing exactly what it’s supposed to do, just much faster than other people’s livers.

Once your ADH1B enzyme converts alcohol into acetaldehyde, another enzyme called ALDH2 has to convert that acetaldehyde into acetate, which is harmless. ALDH2 is the gatekeeper. If it’s working well, acetaldehyde doesn’t stick around. If it’s slow or broken, acetaldehyde accumulates in your blood and tissues. And that’s when things get really uncomfortable.

The ALDH2 Glu487Lys variant (the *2 allele) is found in roughly 35 to 40% of people with East Asian ancestry and is very rare in people with European ancestry. Carrying even one *2 allele significantly reduces ALDH2 function. Carrying two *2 alleles nearly eliminates it entirely. People with the *2 allele experience severe acetaldehyde buildup even after very small amounts of alcohol.

If you have an ALDH2 variant, one drink doesn’t just make you feel a little flushed or tired. It can make you feel acutely ill. Facial flushing happens within minutes. Your heart races. You might feel dizzy, nauseated, or even chest discomfort. The hangover the next day is often severe: intense headache, extreme fatigue, nausea that lasts hours. Some people describe it as feeling genuinely sick rather than just hungover.

Alcohol is metabolized by multiple pathways in your liver. The ADH and ALDH pathways handle the main conversion, but CYP2E1 is a backup pathway that kicks in, especially after heavy drinking or repeated drinking. CYP2E1 doesn’t just convert alcohol into less toxic forms. It generates oxidative stress in the process, meaning it creates free radicals that damage liver cells and other tissues.

CYP2E1 variants affect how much oxidative stress is generated from alcohol metabolism. Certain variants increase CYP2E1 activity, meaning your liver generates more free radicals and more cellular damage for every drink you consume. This damage accumulates over time, and it happens even if you don’t feel severely hungover after individual drinks.

You might not notice CYP2E1 variants acutely. You won’t feel dizzy or flushed the way you might with ADH1B or ALDH2 variants. But over time, repeated alcohol exposure causes more liver inflammation, more fatty liver, and greater long-term liver toxicity risk. If you’re a CYP2E1 fast oxidizer, your liver ages faster from alcohol exposure than someone with a slower variant would.

GSTM1 is a glutathione S-transferase enzyme. Its job is to grab acetaldehyde and other toxic compounds produced during alcohol metabolism and attach glutathione to them, making them easier to excrete. It’s part of your body’s detoxification cleanup crew. Roughly 50% of people carry the GSTM1 null genotype, meaning they don’t produce functional GSTM1 enzyme at all. They’re not sick or dysfunctional from this. They just have less detoxification capacity.

If you carry the GSTM1 null variant, you have significantly reduced ability to clear acetaldehyde and other alcohol metabolites from your body. This contributes directly to hangover severity. You might not feel as acutely ill during drinking as someone with an ALDH2 variant would, but the next day is rough: pounding headache, extreme fatigue, nausea that won’t quit, brain fog that lasts into the afternoon.

You notice that your hangovers are disproportionately bad compared to your friends, even when you drink the same amount they do. You recover slowly. While others bounce back after breakfast and coffee, you’re still wrecked 12 hours later. That’s often GSTM1. Your body is working fine. It’s just working with a smaller toolkit.

COMT is short for catechol-O-methyltransferase. It’s an enzyme that breaks down dopamine and norepinephrine, two stress hormones. Your COMT variant determines how fast you clear these hormones. If you’re a fast COMT clearer, stress hormones don’t stick around long. If you’re a slow COMT clearer, they linger. Now add alcohol to the picture. Alcohol is a depressant. It lowers dopamine and norepinephrine. If you’re already a slow COMT clearer, alcohol drops your stress hormones even further.

The COMT Val158Met variant affects this clearance. Roughly 25% of people with European ancestry are homozygous slow (Met/Met), meaning they clear stress hormones slowly. Slow COMT variants are associated with increased anxiety, mood sensitivity, and emotional intensity during and after alcohol consumption.

You might notice that after one or two drinks, your mood shifts noticeably. You feel more anxious, more sensitive to stress, more likely to ruminate or worry. Or the next day, you experience unexpected sadness or low mood that seems disproportionate to how much you drank. Friends don’t experience this. They drink, they relax, they move on. For you, alcohol triggers mood or anxiety symptoms that linger. That’s not weakness or poor coping. That’s COMT.

SLC6A4 encodes the serotonin transporter, the protein that reabsorbs serotonin from the space between neurons. Serotonin is the neurotransmitter that regulates mood, anxiety, and emotional resilience. The 5-HTTLPR variant determines the function of this transporter. People carrying the short allele have less efficient serotonin reuptake, meaning serotonin stays active in the synapse longer, but also that their serotonin system is more sensitive to disruption.

Alcohol affects serotonin production and function. Roughly 40% of the population carries at least one short allele of the 5-HTTLPR variant. Short allele carriers experience more pronounced mood, anxiety, and emotional effects from alcohol compared to long allele homozygotes. This isn’t because they’re drinking more or because they’re more prone to anxiety in general. It’s because their serotonin transporter makes their mood regulation system more sensitive to alcohol’s neurochemical effects.

You might notice that even modest alcohol consumption triggers anxiety the next day, or unexpected sadness, or emotional sensitivity that your friends don’t experience. You might feel more vulnerable socially after drinking. Or you might notice that alcohol temporarily improves your mood (because it increases serotonin), but then crashes you hard the next day (because serotonin drops as alcohol clears). That emotional rollercoaster is often SLC6A4.