Alcohol tolerance: why it changes, and why a high one is a warning sign

What alcohol tolerance means

In alcohol research, tolerance is a reduction in the intensity of alcohol's effects over the course of repeated use. A 1997 review in the journal Alcohol Health and Research World puts it simply: a person developing tolerance must drink greater quantities to produce the same effect that a lower amount used to produce. The same review also calls it resistance: social drinkers can develop resistance to alcohol's impairing effects over time.

Tolerance can apply to effects on the body, such as a drop in body temperature, and to effects on behaviour, such as impaired coordination. Researchers generally believe it works by the body producing opposite reactions that offset alcohol's effects and restore a stable internal state. That compensating response is usually assumed to grow stronger each time a person drinks and to fade gradually during a period without alcohol.

A 2008 review in Alcohol Research & Health defines tolerance as the diminished response to alcohol over repeated or prolonged exposure, a mechanism that lets the body's processes stay stable in a constantly changing environment. In other words, tolerance is the body adapting to alcohol.

How quickly tolerance builds

Researchers sort tolerance by how fast it appears. The 2008 review describes three kinds, while noting that the processes behind them overlap and are hard to separate.

Brain, liver and habit: three sources of tolerance

The brain and nervous system. The 2008 review describes how nerve cells, and the channels in their membranes, adapt to alcohol at the molecular level. It links this to dependence: repeated, frequent exposure produces a steadily smaller response, and that shift contributes to the development of dependence.

The liver. A 2012 review of alcohol metabolism by Arthur Cederbaum notes that, besides adaptation in the nervous system, people who are dependent on alcohol and do not have liver disease often clear alcohol from the blood faster. This is called metabolic tolerance. One suggested reason is that long-term drinking raises levels of CYP2E1, a liver enzyme that breaks down alcohol. Because the same enzyme handles some medicines, the review notes that this can make those medicines less effective when alcohol is not present.

Learning and setting. In a 1990 experiment with 40 male students who drank 10 to 20 units of alcohol a week, drinking in a setting with the usual cues of drinking increased tolerance to alcohol's effects on thinking and coordination, compared with drinking the same dose in an unfamiliar setting. The same cues also increased the desire to drink. The 1997 review describes tolerance as partly learned and cites animal studies in which tolerance was greater in the familiar setting than in a new one.

Why your tolerance may be lower than it used to be

After a break. Because the body's compensating response is thought to fade gradually without alcohol, the amount you used to drink can have a stronger effect after a dry month or a few weeks off. No source we read gives a number of days or weeks for that change. Start with less than your old amount and count it with our standard drink calculator.

With age. NIAAA says older people are more sensitive to alcohol's sedative effects and to its effects on balance, coordination, attention and driving skills, which raises their risk of falls, car crashes and other injuries. Reduced muscle mass and body water mean some older adults reach higher blood alcohol levels than younger people after the same amount. NIAAA adds that some older adults who have drunk the same amount for years may notice the effects are more pronounced and come on more quickly.

With body size and sex. The same dose per kilogram of body weight can produce very different blood alcohol levels in different people, because bodies differ in their proportions of fat and water. Cederbaum's review notes that women generally reach higher peak blood alcohol levels than men when given the same dose per kilogram.

In an unfamiliar place. Because part of tolerance is learned in the settings where you usually drink, the same amount may affect you more somewhere new.

Why a high tolerance is a warning sign, not a strength

Tolerance is one of the 11 criteria doctors use to diagnose alcohol use disorder (AUD). In NIAAA's summary of the DSM-5 criteria, the tolerance question asks whether in the past year you have had to drink much more than you once did to get the effect you want, or found that your usual number of drinks had much less effect than before. The NHS lists needing increasing amounts of alcohol to get the same effect among the signs of alcohol-use disorder.

One criterion alone is not a diagnosis. Under DSM-5, AUD means meeting at least 2 of the 11 criteria in the same 12 months; 2 to 3 is mild, 4 to 5 moderate and 6 or more severe. The 1997 review also cautions that tolerance seen in behaviour can change with what a drinker expects, so on its own it is unlikely to be a reliable sign of dependence. If you want a standard way to look at your drinking, our AUDIT-C check takes about a minute.

There is also a plain arithmetic problem. Tolerance means drinking more to feel the same, so more alcohol reaches your body. The NHS lists liver damage, many types of cancer, high blood pressure and stroke, and heart problems among the longer-term risks of drinking too much, and NIAAA says older adults could develop alcohol-related problems at lower drinking amounts than younger people.

Lowering your tolerance safely means drinking less

None of the sources we read describes a safe shortcut for resetting tolerance. What they do describe is drinking less. NIAAA's Rethinking Drinking suggests keeping track of every drink, knowing standard drink sizes so you count accurately, and deciding how many days a week you will drink and how many drinks on those days, with some days when you do not drink. Our guides on how to cut down on alcohol and drink-free days turn that into a plan.

Do not stop suddenly if you might be dependent. NIAAA warns that when someone who has been drinking heavily for a long time suddenly stops, the body can go into a painful or even potentially life-threatening withdrawal, with symptoms such as nausea, a rapid heart rate and seizures, and that doctors can prescribe medicines to make the process safer. The NHS says that if you get withdrawal symptoms you should get medical help before you try to stop drinking. Our guide on how to quit drinking safely explains the first steps.

Common questions

When to get help

This site offers self-help tools and information, not medical advice. Talk to a doctor, or call one of the lines below, if:

• you feel shaky, sweaty, sick or anxious when you haven't had a drink;
• you find it hard to stop once you start, or you want to cut down and can't;
• drinking is causing problems with your health, work or the people close to you.

Before you stop: It can be very dangerous to stop drinking suddenly if you are dependent on alcohol. If you get withdrawal symptoms, get medical help before you try to stop drinking.

Sources

1. Vogel-Sprott M (1997). Is Behavioral Tolerance Learned?. Alcohol Health and Research World, 21(2), 161–168. PMC6826826
2. Pietrzykowski AZ, Treistman SN (2008). The Molecular Basis of Tolerance. Alcohol Research & Health, 31(4), 298–309. PMC3860466
3. Cederbaum AI (2012). Alcohol Metabolism. Clinics in Liver Disease, 16(4), 667–685. PMC3484320
4. McCusker CG, Brown K (1990). Alcohol-predictive cues enhance tolerance to and precipitate "craving" for alcohol in social drinkers. Journal of Studies on Alcohol, 51(6), 494–499. PMID 2270057
5. Alcohol Use Disorder: A Comparison Between DSM–IV and DSM–5. National Institute on Alcohol Abuse and Alcoholism (NIAAA). niaaa.nih.gov
6. Aging and Alcohol. National Institute on Alcohol Abuse and Alcoholism (NIAAA). niaaa.nih.gov
7. Alcohol-use disorder. NHS. nhs.uk
8. Tips to Try (Rethinking Drinking). National Institute on Alcohol Abuse and Alcoholism (NIAAA). rethinkingdrinking.niaaa.nih.gov
9. To Cut Down or to Quit (Rethinking Drinking). National Institute on Alcohol Abuse and Alcoholism (NIAAA). rethinkingdrinking.niaaa.nih.gov