Alcohol and your DNA: ADH1B and ALDH2

Genetics explainer · Updated June 2026

The two-step pathway

Alcohol leaves your body through a short relay of two enzymes:

1. Alcohol → acetaldehyde, handled mainly by alcohol dehydrogenase (the ADH enzymes, including ADH1B).
2. Acetaldehyde → acetate (harmless), handled by aldehyde dehydrogenase 2 (ALDH2).

Acetaldehyde is the troublemaker in the middle. It's toxic and classified as a carcinogen, and it's what causes facial flushing, a racing heart, and nausea when it builds up. Whether it accumulates depends on the balance between how fast step one makes it and how fast step two clears it.

ADH1B: how fast you make acetaldehyde

The ADH1B gene comes in variants that differ dramatically in speed. The well-studied variant rs1229984 (His48Arg) produces a "fast" form of the enzyme:

• The fast ADH1B allele converts alcohol to acetaldehyde much more quickly than the common form.
• That means acetaldehyde can spike soon after drinking — even in people whose ALDH2 clearance is normal.

On its own, a fast ADH1B tends to make drinking less comfortable: the unpleasant acetaldehyde phase arrives faster. The fast allele is most common in people of East Asian descent but also appears at meaningful frequencies in some Middle Eastern, European, and other populations.

ALDH2: how fast you clear it

If ADH1B is the accelerator on the first step, ALDH2 is the brakes on the second. The rs671 variant (Glu504Lys) largely inactivates the ALDH2 enzyme:

• Active ALDH2 clears acetaldehyde efficiently.
• Inactive ALDH2 lets acetaldehyde pile up — producing the strong, visible flush reaction.

This is the variant behind the so-called "Asian glow." Because it's the more familiar and dramatic of the two, we cover it in depth — including the genotype table and how to find rs671 in your raw data — in the dedicated ALDH2 flush guide.

Why the two genes interact

The reason these markers are usually discussed together is that the effect depends on both steps at once:

• Fast ADH1B + inactive ALDH2 is the most uncomfortable combination — acetaldehyde is made quickly and cleared slowly, so it builds up fast. People with this pairing often feel unwell after very little alcohol.
• Fast ADH1B + active ALDH2 still makes acetaldehyde quickly, but clears it, so the discomfort is usually milder.
• Common ADH1B + active ALDH2 is the typical "no strong reaction" profile.

This is why two people who both flush can have quite different underlying genetics — and why the flush isn't a single on/off switch.

What it's associated with

A few associations are well established in the research literature:

• Lower alcohol dependence. Both the fast ADH1B allele and the inactive ALDH2 allele are consistently linked to lower rates of alcohol dependence. The leading explanation is simple: when drinking produces acetaldehyde discomfort sooner, people tend to drink less.
• Cancer risk among those who do drink. Because acetaldehyde is a carcinogen, people who carry the inactive ALDH2 variant and drink regularly have an elevated risk of esophageal and head/neck cancers. The risk is tied to alcohol intake, not to the gene alone.

Heavy drinking also tends to show up on routine bloodwork — it's a common reason for elevated liver enzymes, where an AST higher than ALT is the classic alcohol-related pattern.

What it does and doesn't tell you

Your ADH1B and ALDH2 genotypes explain a real, mechanistic part of how you respond to alcohol — the speed of each step in the pathway. They don't dictate your behavior, and they aren't a diagnosis.

For genotype-by-genotype detail, browse the Quanome gene library. For the flush reaction specifically and how to find rs671 in your raw data, see the ALDH2 flush guide. Or explore the rest of the Quanome blog.

Frequently asked questions

What's the difference between ADH1B and ALDH2?

They work on different steps. ADH1B controls how fast alcohol is converted into acetaldehyde — a fast variant makes that first step happen quickly. ALDH2 controls how fast acetaldehyde is then cleared away into harmless acetate. A problem at either step lets acetaldehyde build up, which causes flushing and nausea.

Does ADH1B cause the alcohol flush?

Indirectly. A fast ADH1B variant produces acetaldehyde more quickly, so it can accumulate faster — contributing to flushing and feeling unwell. The classic, dramatic flush reaction is most strongly driven by the ALDH2 rs671 variant, which slows acetaldehyde clearance.

Why are these variants linked to lower alcohol dependence?

Both the fast ADH1B and the inactive ALDH2 variants make drinking less pleasant — alcohol produces acetaldehyde-related discomfort sooner. People who feel sick faster tend to drink less, and population studies consistently associate these variants with lower rates of alcohol dependence.

Where do these variants come from?

The fast ADH1B (rs1229984) and inactive ALDH2 (rs671) variants are both most common in people of East Asian descent, though the fast ADH1B allele also appears at notable frequencies in some other populations. This is educational, not medical advice.