Nicotine dependence / cigarettes per day

The CHRNA5 gene builds part of a nicotine receptor in the brain. A common variant in it changes how that receptor responds to nicotine and is one of the strongest common signals for heavier smoking, stronger dependence and harder quitting, but only in people who smoke.

What this variant does

This variant changes an amino acid in the alpha-5 subunit of the nicotinic acetylcholine receptor, part of the receptor complex through which nicotine acts in the brain, and it alters how that receptor responds. Unlike most behaviour-related variants on this site, this one is a coding change with a demonstrated functional effect.

The behavioural consequence is a measurable shift in how much people smoke once they start, rather than in whether they start at all.

How strong the evidence is

Very. In a study of up to 153,918 people, the association with cigarettes per day reached a p-value below 1e-138, and it has replicated across many populations. ClinVar lists it with three-star review status under lung cancer susceptibility and smoking as a quantitative trait.

It is one of the largest and most reliable common-variant effects on any behaviour, which makes it the exception on a page of behavioural genetics rather than the rule.

The lung cancer link runs through more than cigarette count

Carriers smoke more, which raises cancer risk for the obvious reason. But studies of nicotine metabolites and tobacco-specific nitrosamines found that carriers also extract more nicotine and take in a higher dose of carcinogen per cigarette, so risk remains elevated even comparing people who smoke the same amount.

Carriers have also been found to quit later on average, with one study reporting a median cessation age of 56 against 52 for non-carriers. The variant shifts the whole trajectory of a smoking history rather than one part of it.

What follows from this, and what does not

Nothing here changes the advice, because the advice was already the strongest available: stopping smoking is the single most effective health action there is, and it works regardless of genotype. A high-risk result is not a reason to expect failure, and quit rates in carriers respond to the same treatments, including varenicline and nicotine replacement.

In 1000 Genomes reference data about 45% of European-ancestry individuals carry one copy and 11% carry two, against roughly 5% of East Asian-ancestry individuals, so this is common variation rather than an unusual susceptibility.

What this variant does not tell you

It says nothing about whether someone starts smoking, which is driven overwhelmingly by social environment, price and availability, and it does not predict lung cancer in a non-smoker. It is a variant about how heavily a smoker smokes and what that costs.

What each rs16969968 genotype means

rs16969968 has three possible genotypes: GG, AG and AA.

Typical nicotine response (rs16969968 GG). You carry the common version of CHRNA5, the gene for part of a brain nicotine receptor. If you smoke, your dependence and how many cigarettes you tend toward are in the usual range for this gene. If you never smoke, this variant has no effect on you.

Higher dependence if you smoke (rs16969968 AG). You carry one copy of the CHRNA5 variant that changes how your brain's nicotine receptors respond, which is linked to somewhat stronger nicotine dependence and smoking a bit more if you smoke. It says nothing about whether you'll start, and it has no effect if you never smoke; for smokers it can mean quitting is harder, so extra support or nicotine-replacement help is worth considering.

Strong dependence if you smoke (rs16969968 AA). You have two copies of the CHRNA5 variant most tied to heavier smoking, stronger nicotine dependence and a higher risk of smoking-related lung disease among people who smoke. This only matters if you smoke: it doesn't cause never-smokers any harm and doesn't make anyone start. If you do smoke, quitting is likely to feel harder, so structured support, medication or nicotine replacement can make a real difference.

Evidence & sources

Across global populations, about 10% of people carry two copies of this variant, and about 50% carry none.

This variant appears in 4 published genetic studies: PubMed 29758381 · PubMed 30679032 · PubMed 31294817 · PubMed 40157913.

Common questions

Does this variant make it harder to quit? Carriers smoke more heavily and quit later on average, so in that sense yes. It does not change what works: stopping smoking has the largest health effect of anything on this site, and treatments help carriers as much as anyone.

Does this raise lung cancer risk if I never smoked? No. The risk runs through smoking, both through smoking more and through taking in more nicotine and carcinogen per cigarette. Without smoking, the variant has nothing to act on.

Related

BDNF memory & stress variant (Val66Met) · Coffee consumption · COMT "warrior vs worrier" (stress & dopamine) · Dopamine reward sensitivity (DRD2 Taq1A) · Morning vs evening preference (CLOCK) · Oxytocin receptor / empathy tendency