[♩INTRO].

Throwing up is actually the worst, but at least your body has a good reason for it most of the time, like if you’ve eaten bad seafood or something. But nausea and vomiting are also common side effects of severe pain, whether it’s from a migraine or getting punched really hard, and that seems much less logical.

Like, why would a raging migraine in your head make your body want to empty your stomach? Well, there’s a chance you can blame it on our old friend adrenaline. There’s lot of anecdotal evidence for the link between pain and vomiting, but purposely hurting people badly enough to make them blow chunks for a study is kind of ethically sketchy.

So research on this usually follows surgery patients people who will likely be in pain anyway, and at predictable times. In these studies, patients experienced both pain and nausea after their procedures. And the researchers found that when only the pain was treated, the nausea tended to disappear, too.

At least, the vast majority of the time. That strongly suggested the pain was the source of the queasiness in these cases, not something else about the surgery, like anesthesia. Since pain is so complex, both in terms of where you feel it and how strong it is, it’s difficult for scientists to pin down exactly what mechanism links pain and vomiting.

But they do have some promising ideas, one of which involves hormones like adrenaline. Adrenaline is the stuff that gets your heart pounding before a first date or a big race, and it’s also released when you’re in pain. That’s probably because pain is a sign that something is clearly going wrong.

So by speeding up your breathing and heart rate, adrenaline can prepare your body to escape a potential threat. As part of that preparation, the hormone activates a bunch of receptors throughout your body, including one type called alpha-adrenergic receptors, which might be specifically responsible for the pain-induced vomiting. This hasn’t been directly tested in humans, but in some animals, activation of these receptors can cause neurons to fire in a brain region called the area postrema, a tiny spot in your brainstem more commonly known as the vomiting center.

And like the name suggests, it triggers the numerous systems that lead to revisiting your lunch. So when you’re in a ton of pain, that flood of adrenaline could activate a bunch of these alpha receptors, and therefore your vomiting center. And then it’s hello, toilet.

Then again, the answer could be more complicated. See, while vomiting itself has some pretty clear-cut mechanisms, the causes of nausea are still poorly understood. Studying it is really tough because unlike pain, nausea is more than just a physical signal.

It’s a full-on physical, psychological, and even emotional experience, and that makes it hard to test in animals. It’s not like you can just ask a rat how queasy they’re feeling. So, it’s possible that pain mostly leads to nausea, and that sickly feeling is what makes you throw up, rather than pain directly leading to vomiting.

To learn more, scientists will need to find some way to research this process in humans. But since they can’t just go around punching people until they throw up… first they’ll need to find a safe way to do it. In the meantime, thanks for asking, and thanks to all of our patrons on Patreon who voted to have this question answered!

Hopefully all this talk about vomit didn’t make you too queasy. If you have a science question for us, or want to get access to other cool rewards like exclusive blooper reels while supporting this show, you can go to patreon.com/scishow. [♩OUTRO].