Quick Answer
You get a hangover because alcohol causes four overlapping biological problems: it dehydrates you (by suppressing ADH), creates a toxic metabolite called acetaldehyde faster than your liver can process it, triggers systemic inflammation via cytokine release, and disrupts deep sleep. The combination of these four effects is what you feel the next morning.
The Four Reasons You Feel Terrible
1. Alcohol Makes You Dehydrated (The Diuretic Effect)
Alcohol suppresses a hormone called ADH — anti-diuretic hormone — which normally tells your kidneys to retain water. With ADH suppressed, your kidneys produce far more urine than usual. For every alcoholic drink, you urinate roughly 100-150ml more than you take in.
By the time you go to sleep, you're already significantly dehydrated. Overnight, without drinking water, that dehydration deepens. This causes the classic hangover headache (the brain literally shrinks slightly, pulling on its protective membranes), extreme thirst, and fatigue.
2. Acetaldehyde — The Toxic Middleman
When your liver processes alcohol (ethanol), it doesn't go straight to a harmless compound. It passes through an intermediate called acetaldehyde — a substance significantly more toxic than alcohol itself.
The enzyme ALDH2 converts acetaldehyde into acetate (essentially harmless). But this conversion takes time. When you drink faster than your liver can process, acetaldehyde builds up in your bloodstream. Acetaldehyde causes nausea, flushing, rapid heart rate, and that general sense of being poisoned — because, biochemically, you are.
People of East Asian descent who have a genetic variant of ALDH2 experience this effect much more severely, leading to the "Asian flush" response even from small amounts of alcohol.
3. Inflammation — The Immune System Response
Alcohol doesn't just intoxicate — it triggers your immune system. Studies show that alcohol and its metabolites cause the release of pro-inflammatory cytokines, the same signalling molecules that make you feel terrible when you have the flu.
This explains why a hangover can feel remarkably flu-like: fatigue, body aches, nausea, difficulty thinking, sensitivity to light and sound. It's not just dehydration — it's your immune system responding to perceived damage.
4. Sleep Disruption — The Hidden Factor
Alcohol makes you fall asleep faster but dramatically worsens sleep quality. It suppresses REM sleep — the restorative, dreaming stage — in the first half of the night, then causes a "rebound" effect in the second half that leads to fragmented, restless sleep.
You may sleep for eight hours after drinking and wake up feeling like you slept for three. The quality just isn't there. This is why hangover fatigue is so disproportionate to how much you actually slept.
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Shop Revive Capsules →Why Do Some People Get Worse Hangovers Than Others?
Hangover severity varies enormously between people. The main factors:
- ALDH2 genetics. How efficiently your liver converts acetaldehyde determines how much of this toxic compound lingers in your system.
- Body weight and composition. More body water means more dilution of blood alcohol. Smaller people reach higher blood alcohol concentrations from the same amount.
- Hydration going in. If you're already dehydrated before you start drinking, hangovers are worse.
- Age. Liver efficiency decreases with age. ADH levels change. Recovery takes longer. This is why hangovers objectively get worse as you get older — it's not in your head.
- Sleep. Even poor sleep quality separate from alcohol makes the morning worse.
- What you drank. Congeners — byproducts of fermentation found in darker spirits like bourbon, brandy, and red wine — are associated with more severe hangovers than clear spirits like vodka or gin.
Why Does Drinking Water Help (But Not Cure It)?
Water addresses the dehydration component specifically. It won't neutralise acetaldehyde, reduce inflammation, or restore sleep quality. This is why water helps with hangover headache but doesn't make you feel 100% — the other three causes are still there.
Electrolytes (sodium, potassium, magnesium) are more effective than plain water because alcohol causes you to lose these alongside fluid. A sports drink or coconut water is better than pure water for hangover rehydration.
Can You Prevent It Rather Than Treat It?
The most effective intervention is before-bed rather than next-morning. Here's why: most of the acetaldehyde processing, cytokine release, and ADH disruption happens overnight while you're asleep and can't do anything about it. Supporting your body during this window — with DHM to aid acetaldehyde metabolism, B vitamins to replace what was depleted, milk thistle for liver support, and L-theanine for sleep quality — addresses all four causes proactively.
By morning, the damage is already done. Prevention during the overnight window is fundamentally more effective than trying to treat symptoms after they've fully developed.