We’ve all heard the classic symptoms: headache, nausea, fatigue, and that general feeling of regret. But what actually causes a hangover? While it may feel like your body is punishing you for last night’s decisions, there’s a fascinating (and slightly brutal) biological process behind it all.

1. Dehydration and Electrolyte Imbalance

Alcohol is a diuretic, which means it increases urine production. This leads to dehydration, one of the main culprits behind the pounding headache and dry mouth. When your body loses fluids, it also loses important electrolytes like sodium, potassium, and magnesium, which are essential for normal muscle and nerve function.

2. Inflammation

Alcohol triggers an inflammatory response in your immune system. It can increase the production of cytokines, which are chemicals that help regulate immune responses. In excess, they can cause fatigue, body aches, and difficulties concentrating—the same symptoms you might experience with the flu.

3. Toxin Buildup: Acetaldehyde

As your liver breaks down ethanol (alcohol), it turns into a toxic compound called acetaldehyde. This chemical is significantly more toxic than alcohol itself and can cause nausea, sweating, and vomiting. Normally, the liver quickly breaks acetaldehyde down into acetate (a less harmful substance), but during heavy drinking, this process can be overwhelmed.

4. Blood Sugar Crash

Alcohol can interfere with your body’s ability to regulate blood sugar. After an initial spike, levels can plummet, leaving you feeling shaky, weak, and irritable. Low blood sugar may also contribute to mood swings, fatigue, and dizziness.

5. Sleep Disruption

While alcohol can help you fall asleep faster, it disrupts REM sleep—the stage of sleep linked to dreaming and emotional processing. As a result, you might wake up feeling unrested even after a full night’s sleep.

6. Gastrointestinal Distress

Alcohol increases the production of stomach acid and can irritate the lining of the stomach and intestines. This leads to nausea, acid reflux, and in some cases, vomiting. It also slows down digestion, contributing to bloating and stomach pain.

7. Vasodilation and Headaches

Alcohol causes blood vessels to expand, a process called vasodilation. This can contribute to headaches and the sensation of a throbbing pulse in your temples.

---

How Long Does a Hangover Last?

Most hangovers begin a few hours after drinking stops and can last up to 24 hours. Severity depends on factors like how much you drank, your hydration levels, what you ate beforehand, and individual biological differences.

---

Can You Prevent It?

There’s no guaranteed hangover cure, but these tips can help reduce your risk:

• Stay hydrated (drink water between alcoholic drinks)
• Eat before drinking (especially foods rich in protein and fats)
• Avoid congeners (found in darker spirits like whiskey and red wine)
• Pace yourself (your liver can process about one drink per hour)

---

A hangover is your body’s way of saying: “That was too much.” Understanding the science behind it can help you make better choices—or at least prepare for the aftermath.