‘Poop Pills’ Show Promise for Severe Peanut Allergy, Early Research Shows

• A preliminary study found that “poop pills” — oral fecal microbiome transplantation (FMT) — increased tolerance to peanuts in some adults with a peanut allergy.
• Researchers found similar results in mice, with a certain type of gut bacteria playing a key role.
• While the findings are promising for future trials, it’s too soon to recommend FMT as a treatment for peanut allergy.

A small clinical trial suggests that fecal microbiome transplantation (FMT), or “poop pills,” may increase peanut tolerance in adults with peanut allergies.

The research, published on August 5 in Science Translational Medicine, investigated whether receiving a fecal transplant from a healthy donor could reduce the severity of peanut allergy.

Some participants found that their tolerance to peanuts increased. In an animal model, researchers found that mice receiving FMT from the human participants were also protected against the allergy.

“This landmark study was the first to demonstrate that a microbiome-based therapy may improve food allergy in people while also revealing how gut bacteria, their metabolites, and the immune system work together to influence treatment response,” said study author Rima Rachid, MD, in a news release.

Increase in peanut tolerance in nearly half of participants

Among the study’s 15 participants, 6 experienced increased tolerance to peanuts.

There were two stages to the human trial. In the first stage, 10 individuals received frozen FMT from donors with healthy gut microbiomes. They took 36 pills in either 1 or 2 days. Four months later, 3 in 10 people experienced an increased tolerance to peanuts.

The second stage involved five participants who had taken antibiotics before receiving FMT. The study found that 3 in 5 individuals had an increased peanut tolerance.

Among those who experienced increased tolerance, FMT increased the number of immune cells called RORγt+ regulatory T cells, which help regulate the immune system.

“The first aim of the study was to evaluate for safety in the food allergic population, and none of the patients had serious adverse events,” Rachid told Healthline.

“One of the secondary aims of the study was to evaluate if FMT could increase the threshold dose that patients react to, given the promising data we found in mice. It was very encouraging to see that some patients tolerate more peanut protein following a single dose of FMT,” Rachid said.

Mohammad Bakhtiar, MD, PhD, a general practitioner and clinical lead at Medical Express Clinic, wasn’t involved in the study but shared his thoughts on the findings.

“The gut microbiome already has a major effect on many parts of human physiology so food allergy sitting in that list makes sense,” Bakhtiar told Healthline.

“What this study cannot do is tell us how well it works in the real world; 15 people is a start, but it’s not something that can necessarily apply across populations. Six improved, but nine did not. It is still a tiny, open-label phase 1 study. I would treat it as an early signal, not a change in practice,” he said.

Gut bacteria may play a role in peanut tolerance

Following the trial, researchers sampled the microbiomes of participants with increased peanut tolerance and transplanted them into mice. The mice were then protected against the allergy due to the increased RORγt+ regulatory T cells.

The authors noted that the protection offered by FMT was associated with increased bile acid metabolites in both humans and mice.

The authors noted an increase in bile acid metabolites in both humans and mice.

When the researchers removed bile salt hydrolase, an important enzyme in bile acid metabolism, from the Bacteroides bacteria in mice, they found that the increased peanut tolerance was removed.

These findings in mice suggest that bile salt hydrolase produced by Bacteroides bacteria may help reduce peanut allergy. However, this part of the study was not conducted in humans.

Are ‘poop pills’ the future of peanut allergy treatment?

Current peanut allergy treatments include immunotherapy and biologics. Some people with a peanut allergy also need to carry an epinephrine auto-injector device in case of severe allergic reaction or anaphylaxis.

While the study’s findings show promise, FMT cannot yet be recommended as a treatment for allergies.

Rachid discussed the potential next steps for the research. “We would like to administer a more purified form of FMT, called MTT (microbiota transplantation therapy), that has less than 1% nonmicrobial fecal material,” she said.

“MTT can be stored in a home fridge. We would like to evaluate its effect after prolonged administration, to see if patients can tolerate higher doses, and evaluate if efficacy is more prolonged. It is critical to receive funding to support future trials to advance the microbiome therapeutics in food allergy. With adequate funding support, and if the effect is proven in future trials, it’s possible we might see clinical applications in 10 to 15 years,” Rachid continued.

Bakhtiar agreed that microbiome treatment for peanut allergies could be possible in 10 years, “if the larger trials hold up.”

“You still need bigger studies, a clearer idea of who responds, a safer and more standardized product than whole-stool capsules, and evidence that the protection lasts. What people should do now remains unchanged: strict avoidance, an emergency plan, and specialist allergy care. If a defined bacterial or metabolite treatment comes out of this, that is when the conversation changes,” Bakhtiar said.