How do drugs taken orally pass on the bloodstream?


And how aren’t pills for example destroyed by our stomach acid?

In: 2

The same way nutrients from food are broken down. Food and anything else you ingest is broken down in the stomach and digestive systems, and nutrients and other substances are absorbed by the blood. There are capillaries and other vessels throughout that carry the substances to the rest of the body’s circulatory system.

This is a very simplified explanation of what happens. These things start being broken down by saliva in your mouth and continue on through the intestines. Different substances are absorbed at different points in the body.

Some pills have what’s called an enteric coating on them, which means they will survive the stomach and break down in the intestines instead.

Others will break down in the stomach and be absorbed there. The stomach acid helps break down food in order to make it ready for the body to use.

Basically, because acid doesn’t really break *everything* down, at least not quickly.

You can test this with vinegar, which is fairly close to the acidity of our stomachs. It’s a completely different acid, so the effects won’t be identical, but try dropping stuff in a small cup of straight white vinegar. I just did so with a shot glass and a couple of old pills I had lying around (because Science). The coating on one of the pills dissolved pretty quickly, but even after several minutes of stirring, the pills are still mostly there.

I poured off most of the first run of acid (since it was all cloudy with the coating from the one pill, and to “refresh” the acid–that’s another thing, you have a finite volume of stomach acid, and most of the reactions that it does to break things down also break *it* down to some degree afaik). One of the pills (blood pressure, I think) had dissolved to chalky-looking mush, but the other two (an ibuprofen and a multivitamin, I think) were still mostly intact. (incidentally, I’m writing this as I experiment, so I’m not going back to correct the “still mostly there” assertion, I hadn’t realized I was only fishing up 2 of the 3 pills). And the third pill was still *there*, it just wasn’t solid any more.

I just checked, the probably-blood pressure med also dissolves pretty quickly just in *water*. The acid sped things up, but not by a whole lot. And, again, all the molecules are still there, just in mush instead of in a pill.

So, once your stomach acid and other things (the squishing around your stomach does, the proteases, aka protein-eating enzymes, and so on) break up the pill (and your food), it’s on to your small intestine. A few things start to be absorbed directly from your stomach, by the way (like asprin), but the small intestine is where most of the magic happens.

Your small intestine is basically a long tube (unless something is Very Wrong, a good bit longer than you are tall). It’s designed to absorb things, including having special structures like circular folds, which are about what they sound like, and villi, microscopic finger-like projections, both designed to give it more surface area. All of that surface area is rich with blood vessels, so that the things you eat can get into your blood stream. A lot of special enzymes also get secreted there to break things down further, and there are a bunch of microorganisms that live there and help us digest things we can’t.

Anything that can pass through the lining of the small intestine can get into our blood from there, including oral drugs. If a drug can’t pass through our stomach and small intestine properly, then we have to take it some other way. There is a reason that insulin dependent diabetics need to inject insulin, they can’t just take an insulin pill.


Thanks to Wikipedia, and a few other random sites, for some of this information.

Same way most vitamins, minerals, sugars, and proteins do: through the small intestine. Stomach acid and churning does destroy the physical pill but doesn’t break them down into atoms. If it did, the same would happen to food and we’d starve. The stomach absorbs a little but mostly just makes it into a slurry with most of the the chemical compounds intact but easily accessible so when they pass into the intestines they can be more easily absorbed into the blood or processed by bacteria in our intestines into something we can absorb into the blood.

Anything that isn’t absorbed ends up as poop. Any excess that is absorbed and is filtered out of the blood later ends up as pee.