Is capsaicin actually passed in feces or urine?

[grude]

Old joke about eating something spicy and then experiencing a burn when defecating, I’ve also heard people claiming this and even when urinating.

Is this actually a thing? I have never experienced anything like this, and I’ve eaten some extremely spicy things.

[WhyNot]

Yes, a small amount of it (exact number unknown) is not metabolized and will end up in the urine or feces. So if, like me, you don’t eat a whole lot of capsaicin at once, you’ll probably never feel it burning when you eliminate. If you’re the kind of guy who’s doing shots of Burning Ass Hot Sauce, there’s likely to be enough capsaicin at the exit to feel it. So it’s dose dependent.

Sciencey stuff:

IV. Capsaicin Metabolism
Capsaicin metabolism after oral administration is believed to be similar in the human, rat, and canine microsome. When capsaicin and dihydrocapsaicin reaches the liver, a major part is metabolized; however, the proportion that undergoes metabolism is unclear. In vitro experiments show that the amount of capsaicin and dihydrocapsaicin is greatly reduced after incubation with liver homogenates (Donnerer et al., 1990; Chanda et al., 2008). In situ experiments in rats have shown that the intestinal elimination rate of capsaicin and dihydrocapsaicin is approximately equal to the concentration of radioactivity in mesenteric venous blood, indicating that presumably no metabolism take place in the gut lumen (Kawada et al., 1984).

An in vitro human investigation with hepatic microsomes and S9 fractions (used to investigate involvement of phase 2 metabolisms), showed that capsaicin was rapidly metabolized, producing three major metabolites, 16-hydroxycapsaicin, 17-hydroxycapsaicin, and 16,17-hydroxycapsaicin, whereas vanillin was a minor metabolite (Chanda et al., 2008). Moreover, Chanda et al. (2008) established a model to elucidate the metabolism of capsaicin at various concentrations physiologically equivalent to those obtained after oral ingestion of pepper fruits. They showed that capsaicin metabolism was less extensive at a concentration of 10 μM than at 1 μM (more than 50% direct inhibition of CYP1A2, CYP2C9, and CYP2C19), and the authors suggest therefore that the rate of metabolism is saturable. Although many enzymes may play some role in hepatic drug metabolism, cytochrome P450 (P450) enzymes are quantitatively the most important, and many drug-drug interactions result from the alteration (increase or decrease) in the activities of these enzymes. At the much lower plasma capsaicin concentrations occurring after topical administration, such as via the 8% patch, direct inhibition of any P450 enzyme has not been shown. Because inhibition of CYP2E1 is thought to prevent the metabolic activation of several carcinogens, and because capsaicin is believed to possess anticancer properties, it has been widely inferred that capsaicin is a CYP2E1 inhibitor. This implication, however, appears in only one publication (Reilly and Yost, 2006). There is no information on the ability of any of these compounds to modulate P450 activity and, to the best of our knowledge, the actions of the metabolites 16-hydroxycapsaicin and 17-hydroxycapsaicin are not known.

In vitro studies of capsaicin in human skin have shown slow biotransformation, and most capsaicin remains unchanged; only a small fraction is metabolized to vanillylamine and vanillyl acid (Chanda et al., 2008). This suggests that cytochrome P450 enzymes participate minimally in capsaicin transformation in skin compared with their key role in hepatic metabolism.

Go to:
V. Capsaicin Elimination
Animal studies have shown that capsaicin is eliminated mainly by the kidneys, with a small untransformed proportion excreted in the feces and urine (Leelahuta et al., 1983; Kawada et al., 1984; Surh et al., 1995). It is excreted in both free form and glucuronide form. In vivo animal studies have shown that after 48 h, only a small amount (<10%) of an administered dose was found in feces (Leelahuta et al., 1983; Kawada et al., 1984).

Unravelling the Mystery of Capsaicin: A Tool to Understand and Treat Pain - PMC

[Patty_O_Furniture]

Capsaisin is about 80% absorbed in the duodenum, jejunum and ileum. From there it’s metabolized and its irritant properties neutralized. What remains in the intestine either passes through with no discernible problem, or if there is still a large amount, may cause an inflammatory response in the small intestine. As a response, the intestine steps on the accelerator to get the irritant out asap. The result may be a loose stool or diarrhea. How much of a burn the victim feels ‘down there’ is variable, depending on the dose and speed of evacuation.

[grude]

Thanks to Whynot and Patty, I wonder why it wouldn’t cause a burning sensation along the entire urethra though.

[Patty_O_Furniture]

Thread from 2010: http://boards.straightdope.com/sdmb/archive/index.php/t-558036.html

In that thread the good doctor mentions “capsaicin-induced urethritis”, although Google doesn’t find much on that, so maybe it was a joke.

[Colibri]

@grude

Thanks to Whynot and Patty, I wonder why it wouldn’t cause a burning sensation along the entire urethra though.

This is just speculation, but perhaps the urethra doesn’t have the heat receptors that capsaicin acts on.

Note that while it may cause irritation in the digestive system, it generally doesn’t produce a burning sensation when it’s in the intestines, possibly because of the same reason.

[jz78817]

@Colibri

This is just speculation, but perhaps the urethra doesn’t have the heat receptors that capsaicin acts on.

AFAIK capsaicin is an irritant to almost all mammalian soft tissues. it’s also hydrophobic/lipophilic so I wouldn’t expect any more than trivial urinary excretion of it.

Note that while it may cause irritation in the digestive system, it generally doesn’t produce a burning sensation when it’s in the intestines, possibly because of the same reason.

I’ve experienced that irritation many times, but it’s more of an “OMG I have to crap right now” followed by what I affectionately call “the ring of fire.”

[Folly]

‘Wolf ass’ as a good friend of mine called it back in college.

“Ahhhhhwooooooooooooooooooooooooooooooooooooo…”

[bump]

@Patty_O_Furniture

Capsaisin is about 80% absorbed in the duodenum, jejunum and ileum. From there it’s metabolized and its irritant properties neutralized. What remains in the intestine either passes through with no discernible problem, or if there is still a large amount, may cause an inflammatory response in the small intestine. As a response, the intestine steps on the accelerator to get the irritant out asap. The result may be a loose stool or diarrhea. How much of a burn the victim feels ‘down there’ is variable, depending on the dose and speed of evacuation.

Sounds about right… and with your location as Bangkok, Thailand, you probably agree!

Some of my most uncomfortable and violent… “events” have been the morning after a lot of Thai food, specifically red curry. Indian food will sometimes get me too. Mexican/Tex-Mex, not so much.

[Patty_O_Furniture]

I can take a little heat in the food, but not much. Luckily most meals are made upon ordering here, so I can specify how many chilis I want in my food. Usually it’s a half of a chili for me. I notice some Thai people take three to five or more in their dish. Yikes!

[What_the]

I eat enough hot stuff to experience it during #2 all the time…never ever noticed it re #1 though.

[trmptgn]

@grude

Thanks to Whynot and Patty, I wonder why it wouldn’t cause a burning sensation along the entire urethra though.

As someone who enjoys diced ghost peppers in my food, I can assure you that it sometimes does - at least at the part you’d expect to feel it at. This is generally only if I really over-do the heat, though. It happens more often with the hot sauces since it is hard to judge how many drops will do the trick without going over. The feeling really freaked me out the first time it happened (after a hot wing competition that some ill advised friends challenged me to).