Ask a Scientist: Can I Take PrEP and Fiber at the Same Time?

A question that needs answers!

A few weeks ago Twitter was set on fire (as it often is). The reason was simple: pop star Troye Sivan had uploaded a photo to Instagram featuring various pills he takes, presumably every morning. Someone had reposted the photo to Twitter after identifying one of the pills was for PrEP and three of the others were fiber supplements. And the masses were discoursing: should you or should you not take your fiber at the same time as your PrEP pill?

The official recommendations seemed to be consistent: you should space the ingestion of fiber and your PrEP out by at least two hours. Some even suggested taking one at night and the other in the morning. But a vocal group pushed back, saying that most of it was an urban legend. As they told it, there is no recorded evidence of PrEP failure that has been connected to fiber intake and the guideline is out of an overabundance of caution.

The result calls for something uber-specific: gay science.

"[This issue] just goes to show the importance of diversity in science and medicine because it’s a very specific question," PhD candidate in pharmacology Kyle Planck tells Out. "When someone was designing clinical trials for PrEP, they probably weren't thinking we need to make sure we look at fiber. But that’s something that we know as members of the queer community: the percentage of gay men who take fiber supplementation is probably much higher than in the average population."

So, he devised a way to get a little information of his own.

What We Know

As in most cases, this is a case of everyone being a little bit right. The reality is there is currently a general guideline to space out intake of fiber and almost all medications or supplements because there are recorded instances of fiber impacting absorption. This has been seen in some heart medications in particular. As a result, there is a general recommendation to avoid even the possibility.

"In theory, something about the drug molecules and the fiber molecules associating together and binding each other could happen which would keep the drugs from being available for absorption," Planck (pictured here) says. "Or there's like a physical explanation where because fiber forms a gelatinous mass, that could, in theory, trap things within it, whether it's particles of a pill or on a smaller molecular level, like things could get caught in it."

And while in theory that could happen with PrEP medication, there is no evidence that this has ever happened nor any studies on its possibilities with PrEP. So Planck took it upon himself to make an attempt at getting some sort of initial, unofficial data.

What Was the Experiment?

In order to get some data about whether fiber could cause PrEP failure when taken together, Planck attempted to recreate the environment of the stomach and small intestines in a lab. Taking a liter of acidic water that mirrored the pH levels of the stomach, he heat it to body temperature and set it in a device for it to churn, replicating the stomach.

He then conducted the experiment, dropping in fiber and Truvada pills for PrEP both together and separately, allowing them to dissolve for an hour and a half, and then neutralizing the acid with sodium benoxinate, which the body does in the small intestine. (For a control, he also conducted the experiment with digoxin, a heart medication that has been known to have interactions with fiber that impact absorption.)

After neutralizing, Planck separated the solid gelatinous mass made by the fiber from the liquids that would have been absorbed into the bloodstream and then used a mass spectrometer to determine what molecules were present in the samples.

What Were the Results of the Experiment?

"To be honest, I was shocked," Planck, whose doctoral work often deals with drug solubility. "Before doing this I was in the camp that we probably shouldn’t take them at the same time. But when I ran the numbers, the average drug amount was the same. It was pretty clear that there wasn’t really a difference, and if there was it was negligible."

He tweeted the study in detail on Twitter where he initially came to prominence after discussing his own experience with monkeypox and speaking out on efforts to fight the outbreak.

So What's the Verdict? Should I Take PrEP With Fiber?

Well, it’s still complicated. While Planck’s results were promising, they were one experiment in a lab setting. ("I was not trying to use up my monthly supply of Truvada," he says.) It was also only done with Truvada, and not generic options like Descovy. And even though he didn’t see any difference in this experiment, that’s not conclusive evidence that there is no interaction between PrEP and fiber.

“As a scientist, I really like to follow the science and follow the evidence, and while I’m very proud of the experiment that I did, I would say the quality of the experiment is pretty weak just because it was only done once and it was not done in people," he says. "It’s clear from my experiment that fiber does not bind the drugs that compose PrEP, but whether or not that is the most important dynamic for it being absorbed in your body is still an open question. In the absence of any trials done in humans, waiting two hours is probably what I would do personally."