When you pop a pill, it begins a long and convoluted journey into your stomach, through the twisting intestines, and then into the bloodstream.
But its absorption might be hindered – so much so that it could take an hour longer for the stomach to dissolve oral medications – depending on your posture.
That's the finding of a new study from researchers at Johns Hopkins University who simulated how pills and tablets dissolve in the human stomach and are released into the upper intestine.
They found that the ideal posture for fastest absorption wasn't sitting upright, but leaning to your right.
"We were very surprised that posture had such an immense effect on the dissolution rate of a pill," says Rajat Mittal, a computer scientist studying fluid dynamics at Johns Hopkins School of Medicine.
"I never thought about whether I was doing it right or wrong, but now I'll definitely think about it every time I take a pill."
Less immediate but far more convenient than injecting medications, oral medications are absorbed into the bloodstream through the intestine. To get there, they must first pass through the stomach and the pylorus, a valve that opens and shuts during digestion.
While you might not be so concerned about how fast your body absorbs vitamin supplements, drug absorption has serious ramifications for how quickly painkillers take effect or how steadily medications stabilize blood pressure – not to mention finding the right dosage for women as opposed to men.
So Mittal and colleagues tested four postures using their computer model of a human stomach, which was based on high-resolution body scan images of a 34-year-old male.
Called StomachSim, the model simulated the fluid and biomechanics of a pill moving through the digestive tract and how fast it would be ejected from the stomach into the duodenum, the first part of the small intestine where absorption of nutrients begins.
Taking pills while leaning to or lying on the right side meant the drugs slipped into the deepest part of the computer stomach and were 'dissolved' twice as fast as pills taken sitting upright.
Lying on or leaning to the left side slowed dissolution such that it took up to five times longer to absorb pills in that position compared to an upright posture, where gravity and anatomy are on the stomach's side.
"For elderly, sedentary or bedridden people, whether they're turning to the left or to the right can have a huge impact," Mittal explains.
Previous studies have similarly found lying on the right side quickens the rate at which the stomach empties food into the intestine, and that sitting, standing or reclining to the right also accelerates the absorption of oral drugs.
To take it one step further, the researchers simulated what happens to pill absorption if someone has a condition called gastroparesis, where damaged nerves or weakened stomach muscles stop or slow the stomach from emptying itself properly.
They found that even a small reduction in the simulated digestion power of the stomach led to noticeable differences in how fast it digested and ejected a pill into the duodenum – similar to changes in posture.
"Posture itself has such a huge impact on it, it's equivalent to somebody's stomach having a very significant dysfunction as far as pill dissolution is concerned," Mittal says.
Of course, a lot happens after drugs and food pass through the stomach, into the intestines and finally the bloodstream. Let's also not forget that computer simulations are useful but very simplified models of complex processes.
How much liquid, gas and food you have in your stomach can impact digestion too, but the researchers did not model this.
"Despite these and other limitations, we have demonstrated that computational models and simulations of gastric fluid mechanics can provide useful and unique insights into the complex physiological processes that underlie drug dissolution," the team writes.
How our bodies process medicines may also be somewhat out of our control, thanks to our genes.
In a field called pharmacogenetics, studies of genes encoding enzymes tasked with breaking down compounds shed some light on why people react to the same medications in different ways – differences which can be traced all the way back to our prehistoric cousins, the Neanderthals.
So while your posture seemingly makes a big difference in how fast your body absorbs oral drugs, there's far more to the story than that.
Your best bet for making sure medicines are effective is remembering to take the pills in the first place, and as prescribed.
The study was published in Physics of Fluids.