You've just woken up, dragged yourself into the kitchen and made your morning coffee. After a few quick sips, bam, it's poo time.
This reaction is extremely common, and many people welcome the effects of coffee to aid their morning toilet trip. But why exactly does coffee make us poop?
According to Dr Paul Bertrand, senior lecturer and researcher into gut and neurosciences at RMIT, there are a few possible reasons.
"Coffee has obviously got caffeine in it, so that's probably one of the main culprits, as caffeine is well known to get the bowels moving. Caffeine has a direct effect on the bowels," Bertrand told The Huffington Post Australia.
This is because caffeine can activate the movement, or "relaxing", of the colonic muscles and, as a result, cause bowel movements.
According to Bertrand, another reason why coffee can make you poop is because coffee is a stimulant.
When you have coffee you can get quite 'wired' and jittery, and being in that sort of mood can make you quite anxious. It's a bit like public speaking -- when you feel anxious this can loosen your bowels because it starts producing the stress hormone in the bowels, which causes it to get very unhappy.
"Coffee can have direct effects to make the bowel have more motility (so the muscles loosen a lot more quickly), but it can also make you quite anxious," Bertrand said.
Some people may also metabolise caffeine differently, meaning the effects of coffee -- including diarrohea and anxiety symptoms -- can linger around longer compared to other people.
Another lesser known reason why coffee can induce pooping -- particularly looser stools -- could be an intolerance to lactose from the milk in your morning latte or cappuccino.
"People could also be lactose intolerant. Everybody eventually will be lactose intolerant, as the ability to digest lactose decreases with age," Bertrand told HuffPost Australia.
"In Asian populations, the ability to digest lactose is nearly almost gone by the age of two, but most Western Europeans can digest it into their 60s and 70s. So, as you get older, that giant latte might actually cause upset in that way."
This onset of lactose intolerance can be gradual and slow, so if you notice looser bowels more frequently after a milky coffee, it might be a good idea to see a medical professional.
Gut problems such as irritable bowel syndrome may also be at play for looser stools.
"People can have a lot of little gut problems that come and go, and these could account for some of these things," Bertrand said.
A final reason for why we may poo after drinking coffee is that it's simply the body's morning reaction to get rid of waste from the day before.
"The final reason is a basic physiological fact, which is when you wake up in the morning, you've been asleep and your gut has been fasting all night. If there's some poop loaded up and ready to go, there's a signal that is sent down to your colon to say, 'Hey, there's more food coming, you need to empty yourself out and get ready,'" Bertrand told HuffPost Australia.
"We used to call it the 'make room' reflex but it's called the gastrocolic reflex."
If you're a big coffee drinker and have ever stopped drinking it suddenly, apart from nasty headaches, you may have also experienced a lack of needing to poo. Don't worry -- your bowels should get back into the swing of things soon.
"It might throw things off a little bit, but over time the digestive system would get used to no coffee," Bertrand said.