What Causes a Hangover?

What Causes a Hangover? Symptoms, Science & What to Watch For

After a night of heavy drinking, many people wake up feeling miserable, plagued by nausea, fatigue, brain fog, or an unrelenting headache. These symptoms make up what we commonly call a hangover. It’s a physical response that can range from unpleasant to debilitating, and while it’s often portrayed humorously in popular culture, the science behind hangovers reveals a far more serious reality.

What Exactly Is a Hangover?

A hangover is your body’s delayed response to alcohol. It involves a wide collection of symptoms, including:

• Headaches or migraines
• Muscle aches and general malaise
• Fatigue and lethargy
• Nausea or vomiting
• Dry mouth (often called “cottonmouth”)
• Sensitivity to light and sound
• Anxiety or low mood “hangxiety”

These symptoms usually peak as your blood alcohol concentration returns to zero, once the intoxicating effects wear off and your body enters the clean-up phase.

The Science: What Causes a Hangover?

While scientists still don’t fully agree on every cause, several known factors play a role:

1. Acetaldehyde Buildup

After drinking, your liver breaks alcohol down into acetaldehyde—a toxic substance that causes inflammation and unpleasant symptoms. Some people metabolise this more efficiently due to genetic variations, meaning their hangovers may be milder.

2. Dehydration and Electrolyte Imbalance

Alcohol is a diuretic; it makes your body expel more water and electrolytes. This leads to thirst, dizziness, low energy and cognitive difficulties the next day.

3. Gastrointestinal Irritation

Alcohol inflames the stomach lining and boosts acid production, which can explain the nausea, stomach cramps, or even vomiting you may experience.

4. Liver and Systemic Stress

Your liver, kidneys, and endocrine system work overtime to process alcohol and its byproducts. A hangover can be the result of these systems being temporarily overworked.

5. Congeners in Alcohol

These are chemical byproducts found more abundantly in darker spirits like whiskey, brandy, or red wine. Some studies suggest that congeners (the chemical byproducts that are caused by fermentation or ageing of alcohol in the gut) may intensify hangover symptoms, but more research is needed.

When It’s More Than a Hangover: Know the Danger Signs

While hangovers are uncomfortable, they typically pass with rest, hydration, and time. However, alcohol poisoning is a medical emergency and can be mistaken for a severe hangover. Symptoms to watch for include:

• Confusion or difficulty staying awake
• Slowed or irregular breathing
• Seizures
• Vomiting repeatedly or uncontrollably
• Pale, cold, or bluish skin

If someone is displaying these symptoms, seek medical help immediately. Do not assume they’ll “sleep it off.”

A Hangover Can Be a Warning Sign

Regular or severe hangovers may be a sign of an unhealthy relationship with alcohol. If you’re finding it harder to stop once you start, or if hangovers are impacting your health, mood or relationships, it may be time to explore support.

At Smarmore Castle, we offer evidence-based residential treatment for alcohol dependency, where medical detox, therapy and holistic care come together to support lasting recovery. We treat addiction as a medical condition, not a moral failing, and we’re here to help you or your loved one start again, safely and confidently.

Recovery is the end of hangovers. You never have to wake up feeling sick as a result of uncontrollable drinking again. At Smarmore Castle Private Clinic, we know that real change is possible. Our residential detox and treatment programmes for alcoholism and alcohol misuse help patients return to optimum health of mind, body, and spirit. Call to speak with one of our caring and attentive staff members today to plan your course of treatment: 041 986 5080