Who wins that (internal) fight?

Only one way to find out!

There are better than I, tho username checks out

A heart attack, I would presume. Depending on what the substances target and how, blood vessels along the colon might experience a rapid switch between widening and constraint, leading to a very unpleasant event.

But I'm no doctor, so I can be wrong about it quite easily.

Based on my experience of having diarrhoea and constipation, it will be really difficult to begin but once you clear the "plug" it'll be runny and come out quickly. I don't know if this is exactly how those things work so that might be more extreme than the result you'd actually get.

Your butthole takes a screenshot

Like a roller-coaster?

Also do you use an iPhone?

Stool hardener? That's a really colloquial thing, there's not a class of meds you'll run into that gets called that. Tbh, I'm moderately confident it's a very recent AI created term, because that's the only references to the term I could find, and I looked.

Only actual products I found were for dogs.

So, I gotta make assumptions here. Caveat: not a doctor, and this ain't for a grade. That means I'm not going into niggling detail for pedants. This is layman level shit that serves as an overview. So, I'll make fun of anyone trying to treat it otherwise.

First, that it has to be a medication, not a diet program. Second that it has to be a med that's targeted to bowel issues. That means that even if it isn't the primary user of the medication, it is at least prescribed or sold for that purpose rather that it being an untargeted sise effect that in turn needs to be countered.

Which leaves a fairly limited range of options. Luckily, they have very similar functionality. Not exactly the same, but close enough for a casual thought experiment as opposed to passing a test on pharmaceuticals.

So, with that in mind, the key thing they do is alter bowel motility. They do it differently, but that's what makes it so that more water is pulled out of the waste, thus "hardening" it.

Laxatives, however, tend to do exactly the opposite. Again, they do it in a wide array of ways, but the ones that meet the criteria of being used to make your bowels move do it by increasing motility.

Laxative vs "hardener" or anti-diarheal.

Essentially, you'll have a slower moving but messy poop in most cases. You are also likely to have cramping that may be painful.

As the bowel slows down via the action of drugs, the bowels have more time to pull water out. If the laxative only increases bowel motility, it comes down to which effect is stronger. You'll either have slightly firmer stools, or slightly looser.

However, some laxatives either also, or only, function by changing the stool directly rather than targeting the bowel. That's stuff that adds fats or sugars or types of fiber or whatever. Those will do little to speed up the bowel, if anything, when a medication is targeting the bowel to slow it down. Most of the time, that's going to result in relatively smooth and easy bowel movements. It can lead to constipation though.

That being said, if you're chugging mineral oil, ain't nothing going to stop it from spraying out because there's no water to remove. You'll have a greasy and likely painful anal explosion. Most of the sugar based laxatives are going to leave things fairly firm, but oils? Hooooo boy! I've had to dodge mineral oil poo sprays before, and it oughta come with a gold medal and a wheaties endorsement because you gotta be fast.

Something like a senakot, which irritates the bowel as opposed to stimulating it less directly, that's where you run into the immovable object vs irresistible force concept. Most of the time, it will take a higher dose of something otc to counter a normal dose of senekot (spelling? I can never fucking remember, and don't care enough to look it up). So if you take one immodium and one senekot, expect a painful, crampy bowel movement that manages to be chunky rather than outright watery the way senna often makes it. Which is still less explosive than oil laxatives in my experience.

I guess the summation is "it depends".

Ngl, i sorta co-opted it from something i heard passively with Family Guy in the background

Nothing wrong with that :)

You shit bricks i suppose. Nothing like a bit of medical uncertainty to ruin your day.