Understanding Hangovers: Causes & Myths

Dehydration

Alcohol suppresses a hormone that helps the body retain water, increasing urination and contributing to the dehydration many people feel the next day. This effect is generally strongest with higher-alcohol drinks and larger quantities, and it compounds over the course of a drinking session, which is part of why later drinks in an evening can lead to more noticeable fluid loss than earlier ones. Dehydration is commonly associated with several familiar hangover symptoms, including headache, dry mouth, dizziness, and fatigue.

Alongside water loss, drinking can also affect the balance of electrolytes such as sodium and potassium, which play a role in normal muscle and nerve function. This is one reason some people find that rehydrating with an electrolyte drink, rather than plain water alone, feels more effective — though the evidence on this varies and plain water remains a sensible general choice.

Congeners

Darker spirits and drinks tend to contain more congeners — byproducts of fermentation and aging — which some research associates with worse hangover symptoms than clear spirits. Congeners are chemical compounds produced during fermentation and, in aged spirits, during the aging process itself; drinks like bourbon, brandy, and red wine tend to contain more of them than vodka, gin, or white wine. Some studies comparing bourbon to vodka, for example, have found that participants who drank bourbon reported somewhat worse next-day symptoms, though individual results vary considerably and congeners are only one of several contributing factors.

It's worth noting that switching to a lower-congener drink is not a guarantee of avoiding a hangover altogether — the total amount of alcohol consumed remains a major factor regardless of drink type, and other contributors such as dehydration and sleep disruption apply to any alcoholic drink.

Sleep Disruption

Alcohol changes normal sleep patterns, often producing shorter, lower-quality rest that contributes heavily to next-day fatigue. Even when alcohol helps someone fall asleep more quickly, it tends to disrupt sleep in the second half of the night, leading to more frequent waking and less time spent in the deeper, more restorative stages of sleep. This general pattern is covered in more detail in our article on alcohol, sleep, hydration, and recovery.

The combination of shorter total sleep time and lower sleep quality is one of the more consistently cited contributors to how tired and low-energy people commonly feel the day after drinking, independent of dehydration or other factors.

Low Blood Sugar and Digestive Effects

Alcohol can affect how the body regulates blood sugar, and some people report symptoms such as shakiness, fatigue, or difficulty concentrating the morning after drinking that are commonly associated with this effect. Alcohol can also irritate the stomach lining and slow digestion, which is part of why nausea, stomach discomfort, or reduced appetite are frequently reported alongside other hangover symptoms.

Skipping food while drinking, or drinking on a largely empty stomach, is generally associated with more pronounced effects the next day, which is part of why eating before or during a drinking session is commonly recommended as a general, sensible habit.

Inflammation and Immune Response

Some research suggests that drinking triggers a temporary immune response, including markers of inflammation, and that this response may contribute to some of the more general, flu-like symptoms — such as fatigue, reduced concentration, and an overall feeling of being unwell — that some people experience as part of a hangover. This is an active area of general research rather than a settled explanation, and it likely works alongside the other factors described on this page rather than instead of them.

Common Myths

Claims that a specific food, supplement, or 'hair of the dog' reliably cures a hangover are not well supported by evidence; time, hydration, and rest remain the main factors in recovery. 'Hair of the dog' — drinking again to relieve hangover symptoms — may temporarily mask some symptoms by delaying withdrawal-like effects, but it does not address the underlying causes and simply postpones them, generally not a practice recommended by health professionals.

Other commonly repeated ideas, such as specific food combinations, particular vitamins, or over-the-counter hangover remedies, have limited or mixed evidence behind them. Some people find that certain habits — eating a balanced meal, staying hydrated, and getting rest — make them feel more comfortable, but no product or trick has been shown to reliably eliminate a hangover once it has started; the most consistently supported approach remains prevention, primarily through moderating how much is consumed and pacing it with food and water.

Does Drink Type Matter?

Beyond the general congener difference between dark and clear spirits, some people report that certain drink types seem to produce worse hangovers for them personally than others, even at similar alcohol content. This can be influenced by a combination of factors — congener content, carbonation (which some research suggests may speed alcohol absorption), added sugar, and simply how much of a given drink someone tends to consume in one sitting. Because these factors interact in individual ways, general statements about which drinks are 'worse' should be treated as broad tendencies rather than fixed rules that apply to everyone equally.

Hangover Anxiety

Some people report a cluster of next-day psychological symptoms — including low mood, anxiety, and regret about the previous evening — sometimes informally referred to as 'hangxiety.' General research suggests this may relate to alcohol's effects on mood-regulating chemicals in the brain as they return to their normal balance, alongside disrupted sleep and dehydration. As with physical hangover symptoms, time, rest, and hydration are generally the main factors associated with these feelings easing, and persistent low mood or anxiety — whether or not connected to drinking — is worth discussing with a healthcare provider.

General Prevention Habits

Because hangovers are generally understood to result from a combination of factors — the total amount of alcohol consumed, dehydration, disrupted sleep, and individual sensitivity — general public health guidance tends to focus on prevention rather than cure. Commonly cited general habits include pacing drinks across an evening, alternating with water, eating beforehand, and choosing to moderate overall amounts, all of which are discussed in more detail in our article on alcohol, sleep, hydration, and recovery. None of these habits eliminates the possibility of a hangover, but they are the general, evidence-informed habits most consistently associated with a more comfortable next day.

Hangovers and Age

Some people report that hangovers feel more pronounced as they get older, even at similar amounts consumed to what they drank earlier in life. General explanations offered for this include gradual changes in how the body processes alcohol over time, changes in general sleep quality with age, and simply a lower general tolerance for the after-effects of disrupted sleep and dehydration. This is a general, widely reported pattern rather than a precise, universal rule, and individual experiences vary considerably.

When a Hangover Is More Than a Hangover

Typical hangover symptoms — headache, fatigue, nausea, and general malaise — generally resolve within a day. Symptoms that are unusually severe, that don't improve with rest and hydration, or that raise other health concerns are worth discussing with a healthcare provider rather than assuming they're simply a bad hangover. This general page is not designed to help distinguish between the two, and a healthcare professional is always the appropriate resource for assessing symptoms that concern you.

Mixing Drink Types

A commonly held belief is that mixing different types of alcoholic drinks in one session — for example, beer followed by wine followed by spirits — makes a hangover worse regardless of total alcohol consumed. Most general explanations for this suggest that mixing drinks often leads to drinking more overall, or losing track of total consumption, rather than the mixing itself having a distinct chemical effect. Total amount of alcohol consumed, pacing, hydration, and food are generally considered more directly relevant factors than the specific combination of drink types, though congener content (discussed above) can still vary between the drinks being mixed.

The Role of Genetics

General research suggests that genetic differences in how efficiently the body processes alcohol and its byproducts may make some people more prone to pronounced hangover symptoms than others, even at similar amounts consumed. This is consistent with the broader pattern of individual variation discussed in our article on how alcohol affects the body, and it's part of why comparing your own hangover experience to someone else's is generally not a very reliable guide to your own drinking.

• Hangovers
• Alcohol & Health