The day after drinking feels off because alcohol affects several systems at once. It pulls fluid out of your body, breaks up your sleep, irritates your stomach, raises inflammation, and leaves your brain rebounding from the evening. No single cause explains all of it.

Below: each cause, what helps, and what a pre-drink supplement can and cannot be expected to do. We rely on the National Institute on Alcohol Abuse and Alcoholism (NIAAA) and on peer-reviewed reviews, and we say where the evidence runs out.

What "feeling off" actually is

Researchers call it a hangover: a set of symptoms that follow drinking too much. The NIAAA lists fatigue, weakness, thirst, headache, muscle aches, nausea, stomach pain, sensitivity to light and sound, anxiety and irritability as typical. It also says a hangover varies from person to person.

In practice that can mean waking up tired, thirsty and low on energy. Several causes add up, and they are listed below.

What causes a hangover

Six things overlap: fluid loss, broken sleep, an irritated stomach, inflammation, alcohol's byproducts and a rebound in the brain. Researchers still debate how much each one matters.

Mild dehydration

Alcohol suppresses vasopressin, a hormone that tells your kidneys to hold on to fluid. You urinate more and lose more water than usual. The NIAAA says the resulting mild dehydration likely contributes to thirst, fatigue and headache.

The word "likely" matters. A review of human blood and urine studies found that markers of dehydration, including vasopressin, were not significantly related to how severe a hangover was. Staying hydrated is sensible. It is not a complete explanation.

Disrupted sleep

You may fall asleep faster after drinking, but the NIAAA says your sleep is fragmented and you tend to wake earlier.

Stomach irritation

Alcohol directly irritates the stomach lining and increases acid release, according to the NIAAA. That can mean nausea and stomach discomfort the next morning.

Inflammation

Alcohol increases inflammation in the body, and inflammation contributes to the run-down feeling of being sick. In two studies re-analyzed by a research group in the Netherlands, hangover severity rose along with blood markers of inflammation. The markers included interleukin-6, tumor necrosis factor-alpha and C-reactive protein. That is a correlation, not proof of cause. An earlier review called the immune link the most convincing biological finding it examined.

Acetaldehyde and how fast you clear alcohol

Your liver breaks alcohol down into acetaldehyde, which the NIAAA describes as a toxic, short-lived byproduct that contributes to inflammation in the liver, pancreas, brain and gut. Acetaldehyde gets a lot of attention, but the research is mixed. A 2020 review found that blood ethanol was linked to hangover severity, while the link to acetaldehyde was not significant. It also found that people who cleared ethanol faster tended to report milder hangovers. Some earlier studies did find a link.

Congeners and other ingredients

Congeners are compounds, other than ethyl alcohol, that form during fermentation. The NIAAA says darker spirits such as bourbon tend to contain more of them and could worsen symptoms for some people. The earlier review groups congeners with factors that do not cause a hangover but can aggravate one.

The mini-withdrawal

While you drink, you may feel calm and relaxed. The brain quickly adjusts to that, and when the effect wears off, the NIAAA says people can feel more restless and anxious than before they drank.

How long it lasts

Symptoms peak when your blood alcohol concentration returns to about zero, and they can last 24 hours or longer, according to the NIAAA.

The NIAAA also warns that during a hangover your attention, decision-making and coordination can be impaired, which can affect driving or caring for others.

What helps a hangover

Time is the one thing the NIAAA says helps. Its fact sheet states that there is no cure for a hangover other than time. That is because your body has to finish clearing alcohol's byproducts, rehydrate, heal irritated tissue and restore immune and brain activity.

What does not help

• Coffee or a shower. The NIAAA says neither cures a hangover.
• "Hair of the dog." A morning drink might ease some symptoms briefly, but the NIAAA says it could prolong them.
• Pain relievers taken carelessly. The NIAAA warns that alcohol combined with acetaminophen can be toxic to the liver, and that aspirin and ibuprofen can irritate the stomach lining. Ask a pharmacist or doctor before using them around alcohol.
• Counting on electrolytes. The NIAAA says research has not found that added electrolytes change hangover severity, and most bodies restore balance on their own.

What supplements and hangover pills can and cannot do

The evidence for any hangover product is limited. A 2005 BMJ review of eight trials found no compelling evidence that the interventions tested prevent or treat a hangover. A 2017 systematic review of six controlled human studies found that some products improved some symptoms, such as tiredness, nausea and stomachache, but none helped with all of them. It also said more research is needed.

Those reviews covered specific products, from plant extracts to drugs, not every supplement on a shelf. The proof is thin, the trials are few, and the NIAAA says no remedy has been scientifically proven.

Regulators have taken a firm line, too. On July 29, 2020, the U.S. Food and Drug Administration issued warning letters to seven companies whose products claimed to cure, treat, mitigate or prevent hangovers. The FDA said products making those claims are unapproved new drugs, even when labeled as dietary supplements. It added that consumers should not rely on them as an alternative to limiting how much they drink.

A good rule of thumb: be wary of any product that promises to cure, prevent or erase a hangover. No capsule changes how impaired you are, and none makes drinking safe.

Why no product replaces moderation

The only surefire remedy for a hangover is to avoid one by drinking in moderation or choosing not to drink. The BMJ review reached the same conclusion: the most effective way to avoid the symptoms is abstinence or moderation.

If you are 21 or older and choose to drink, eat first, keep it moderate and never drive after drinking. The NIAAA notes that coffee does not sober you up, and alcohol keeps entering the bloodstream from the stomach and intestine after the last drink. If you are pregnant, nursing, taking medication or have a medical condition, ask a healthcare professional before using any supplement. If you dread the day after more often than you would like, that is worth raising with one too.

About First Round

This is product information, not a remedy for anything described above. First Round is our pre-drink dietary supplement, and it will not prevent intoxication. You take 4 capsules with water 30 to 60 minutes before drinking alcohol, and you should not exceed 8 capsules in 24 hours.

Our two label claims are "Supports next-day performance.*" and "Enhances energy and mental clarity.*"

Each of First Round's 13 ingredients is listed at its dose, with no proprietary blends. You can see the full label on the First Round facts page or on the First Round product page, and the timing details are in our guide to when to take a pre-drink supplement.

Frequently asked questions

Why do I feel anxious the day after drinking?

The NIAAA describes a mini-withdrawal. While you drink, you may feel calm, but the brain adjusts to that, so when the effect wears off you can feel more restless and anxious than before. The NIAAA lists anxiety among the typical symptoms. If anxiety is frequent or severe, talk with a healthcare professional.

How long does a hangover last?

According to the NIAAA, symptoms peak when blood alcohol concentration returns to about zero, and they can last 24 hours or longer. How long yours lasts depends on how much you drank and on your own body. The NIAAA notes that people differ so much that it is hard to predict how many drinks will bring one on.

What actually helps a hangover?

The NIAAA says only time helps, since the body must clear alcohol's byproducts, rehydrate and heal irritated tissue. Drinking water and resting give your body room to do that. Coffee and a morning drink do not cure a hangover. The surest approach is to drink in moderation or not at all.

Can a supplement replace drinking less?

No. The NIAAA says the only sure way to avoid a hangover is to drink in moderation or not at all. The evidence for hangover products is limited. A BMJ systematic review found no compelling evidence that any intervention prevents or treats hangover, and a 2017 review found some products improved some symptoms but none improved all of them. Supplements do not change how impaired you are.

Why are hangovers worse with age?

They may not be. In an online survey of 761 Dutch drinkers aged 18 to 94, hangover severity and frequency declined with age, even after adjusting for estimated blood alcohol concentration. The data was self-reported, and individual experience varies. If you feel you do not bounce back as you used to, how much you drank matters too, since more alcohol generally means a worse hangover. See our FAQ for more.

How we wrote this

This article was written by the Supreme Balance Editorial Team. Supreme Balance makes First Round, a pre-drink dietary supplement, so we have a commercial interest in this topic. We link our sources below, we describe what the research does and does not show, and nothing here is medical advice. Last updated November 1, 2026.