How do hangovers work?


what is the science behind it? how can you get symptoms of sickness without actually being sick? why does your body respond that way?

In: Biology

A lot of the symptoms are caused by the dehydration. Alcohol is a diuretic. It causes your body to remove fluids from your blood through your renal system, which includes the kidneys, ureters, and bladder, at a much quicker rate than other liquids

Alcohol is poisonous. Filling your body with poison is generally not a good thing, so your liver has evolved to be able to convert that poisonous alcohol into harmless acetic acid (which can even be further broken down into carbon dioxide, releasing some useful energy in the process – this is why alcohol has calories). Unfortunately, there’s an intermediate step here. Alcohol cannot be directly converted to acetic acid, it first has to be converted into something called acetaldehyde, which is *way* more poisonous than alcohol is.

The steps your body goes through after drinking alcohol depends on the quantity of alcohol and acetaldehyde in your blood. When you’re drinking, you have a lot of alcohol and not much acetaldehyde, so you get to experience the stuff alcohol does – the fun of your brain not working properly. During a hangover, most of that alcohol is now acetaldehyde, so alcohol is no longer inhibiting your brain’s ability to tell itself not to do stuff (including not to feel pain), and instead you get a whole bunch of acetaldehyde toxicity, combined with the pains of dehydration, sleep deprivation and a range of other things that all individually suck and are all going on at the same time.


Here is a great snippet of an NPR segment about homeostasis.

“When we do something that’s pleasurable, for example, when I eat a piece of chocolate, then my pleasure-pain balance tilts just a little bit to the side of pleasure, and I experience release of dopamine in my brain’s reward pathway. But one of the governing principles regulating this balance is that it wants to remain level, which is what neuroscientists call homeostasis. It doesn’t want to be deviated for very long, either to the side of pleasure or pain – so that when I eat a piece of chocolate, immediately, what my brain will do is adapt to the presence of that pleasurable stimulus by tipping my balance in equal and opposite amount to the side of pain. And that’s the after effects or the comedown or, in my case, that moment of wanting a second piece of chocolate. Now, if I wait long enough, that feeling passes, and homeostasis is restored.”

Another snippet from that same interview:

“So the way that I think about it or visualize it in my brain is that after I have a pleasurable experience – like, I have a piece of chocolate – then these little gremlins hop on the pain side of my balance to bring the balance level again. But the gremlins really like it on the balance. So they don’t get off. Again, they stay on until my balance is tipped an equal and opposite amount to the side of pain. And again, that’s the aftereffect or the hangover or the comedown. Now, with waiting, the gremlins hop off, and balance is restored, but the gremlins never entirely go away. They’re sort of left in our brain. They’re the neuroadaptation gremlins, which means that if I do eat a second piece of chocolate, my gremlins are ready to go, right? I Don’t need to create them. They hop right on the balance. And in fact, they tip that balance harder and longer to the side of pain. So what that means is, with repeated exposure to any pleasurable experience, the initial stimulus of pleasure gets weaker and shorter, and the aftereffect of pain gets stronger and longer, which means that over time, I need more and more of the initial stimulus to get the same effect. And this is what’s called tolerance, needing more of the drug to get the same effect or finding that over time, the same dose of the drug has less of an impact.”

>how can you get symptoms of sickness without actually being sick

By “sickness” do you mean infected with some virus or bacteria, like having a flu? Not every “sickness” requires being infected with something. If you don’t drink enough water and get dehydrated, you get the symptoms of that (headache etc) and I’d say that *is* a form of “being sick”. If you ingest poison, that can make you sick too.

BTW, a hangover is those two things I just described! It’s the physical after-effects of drinking too much of a toxic substance, plus very likely being dehydrated at the same time.

>why does your body respond that way

Because you’re literally poisoning it. Your liver does a good job of not letting the alcohol itself build up, but what it turns the alcohol into is also somewhat toxic. Between damage by the alcohol itself and its byproducts, you can’t drink too much poison and get off completely scott-free.