Can You Take PrEP With Fibre?

Update from Dr George (2026): play it safe and keep them apart

Since I first wrote this, I've kept digging, and I want to be straight with you. The experiment below is a clever home lab test, not a formal study in real bodies. It checked whether PrEP still dissolves when fibre is in the mix. It didn't measure the drug levels in anyone's blood, which is the thing that actually protects you.

There's also a mechanism worth respecting. Part of PrEP is absorbed high up in the gut, early in the small bowel, so a thick fibre gel passing through at the same time could still get in the way. We can't rule that out yet.

So here's my current advice: don't take PrEP, or any medication you rely on to stay safe, at the same time as Metamucil or other fibre. Separate them by at least 4 hours. Tablet in the morning, fibre at night, or the other way around. The rest of this page is still worth a read. Just read it through that lens.

For many gay men, a daily regime of PrEP and fibre supplements like Metamucil(tm) has kept us ready for sex without worry.

There has been a long-standing question about whether taking your Truvada, or generic PrEP tablets, at the same time may lead to decreased drug absorption. Reduced absorption could mean a drop in its protection against HIV infection.
The concern was, if the tablet is caught in the middle of the fibre clump, the medicine may not dissolve and be absorbed.

Until this month, it has never been explored with a formal study.

Please welcome to the stage the fantastic science explorer Kyle Anthony who has created an experiment to tackle this question.

Long story short, Kyle replicated the stomach conditions in the lab. He ran two experiments where he dissolved generic PrEP tablets in a water solution compared to a solution of water and a standard dose of fibre tablets.

After mixing for 90 minutes, the average time food sits in the stomach, he tested the liquid for levels of the two drugs in PrEP - Tenofovir and Emtricitabine.

His study showed the drug levels were the same for water and water plus fibre conditions.

To be sure his study was accurate, he did the same test with a drug known to have absorption problems with fibre, Digoxin. This test version did show a drop in the drug levels.

The Digoxin check is clever. It shows the setup can pick up a fibre interaction when one exists, so the test isn’t flying blind. But a jar on a bench still isn’t a human gut, and measuring whether a drug dissolves isn’t the same as measuring how much of it makes it into your bloodstream.

And that’s the heart of it. This is interesting, curiosity-driven research. It is not a formal scientific study. When the drug in question is one you rely on to stay HIV negative, “probably fine” isn’t the bar we work to. The same goes for any medication that matters. Before anyone can safely say fibre and PrEP can share the same glass of water, we need proper research in real people, measuring the actual drug levels in their blood over time. That research hasn’t been done yet. Until it has, I’m not willing to assume.

So what does this mean? To quote Kyle:

“Taking PrEP and fibre together probably doesn’t affect the absorption of PrEP into the bloodstream because the presence of fibre does not affect the PrEP’s solubility.”

He does add a level of caution to this:

” If it were me, I’d probably avoid taking fibre and any medication at the same time since we don’t know if a fibre interaction exists for most meds. But it’s likely not an issue if you currently take PrEP and fibre together.”

If you’ve been taking PrEP and fibre together up to now, don’t panic. It probably hasn’t wrecked your protection. But from here on, separate them, for the reasons I set out up top.

I would add, as has Kyle, that: If you are taking a drug that is vital to staying alive, I recommend separating the fibre and the tablet by at least 4 hours.

I tell my patients, “Take your tablet in the morning and your fibre at night, or vice versa.”

With PrEP, when taken daily, it doesn’t matter what time you take it, so there is scope to separate taking your fibre and PrEP.

Huge kudos to Kyle for tackling a question the rest of us were only wondering about. Grassroots curiosity like this is exactly what should prompt a proper study. I recommend following his work! @KylePlankton

Stay safe, team!

Dr George Forgan-Smith

TL;DR? A home experiment suggests fibre may not block PrEP’s absorption, but it wasn’t a study in real bodies, so we can’t be sure. Until we know, keep your PrEP and your fibre at least 4 hours apart.

This information is general in nature and not a substitute for personalised medical advice. Speak to your doctor or pharmacist about your specific medicines and how to take them.

— Dr George Forgan-Smith, GP, practising in Sydney and Melbourne