Some clinical trials have had disappointing results, but some people with diseases are willing to try to parasitic worms as an alternative treatment.

Thousands of people are intentionally exposing themselves to parasitic worms to treat inflammatory bowel disease, hay fever, and other ailments.

And some of them report that it’s working.

A growing body of research suggests that parasitic worms, also known as helminths, may be useful for treating a variety of autoimmune and allergic conditions.

But to date, the Food and Drug Administration (FDA) has approved no helminths for use in humans in the United States.

Without FDA approval, doctors are unable to provide helminths to patients here.

So, some people are resorting to self-treatment instead, obtaining the worms from places in other countries.

In a study published in 2015, investigators estimated that 6,000 to 7,000 people around the world were self-treating with helminths.

“The modern history of self-treatment goes back to about 2005, when a guy named Joel Weinstock determined that a particular helminth would resolve inflammatory bowel disease for many patients who were not responding to medication,” William Parker, PhD, co-author of the study and director of the Immune Dysfunction and Evolutionary Mismatch Laboratory at Duke University, told Healthline.

“But it became apparent, I think, to many people that it was going to take a long time for helminths to make it through the traditional pathway,” he added. “So within a couple of years, we had two companies selling helminths to people wanting to try it.”

Now, at least five companies around the world sell one or more species of helminths for therapeutic use.

Many of their clients learn about helminth therapy through social media and other community networks.

“This phenomenon is like any kind of social phenomenon,” Parker said. “You have some pioneering individuals who’ve read about it in a scientific paper and go out and try it. If they have a good experience, then more people will try it, and more, and more.”

Critics argue that helminth therapy is dangerous and can cause symptoms of parasitic infection, but some people believe it’s worth the risk.

For some people, helminth therapy offers hope when conventional treatments have failed.

“There will be differing views about this, as to whether it’s a good thing or a bad thing. But I guess if you’re not getting benefits from anything else, I can understand why people would want to do this,” William Harnett, PhD, a professor at the Strathclyde Institute of Pharmacy and Biomedical Sciences, told Healthline.

“I think in many cases, these are people who haven’t gotten any real benefit for their condition from conventional medicine, and so they’re keen to try anything that might be an alternative therapy. And in some cases, they do seem to be getting benefits from that,” he continued.

Four species of helminth are currently available for commercial sale. They are human hookworm, human whipworm, porcine whipworm, and rat tapeworm.

Human hookworm and human whipworm are species of roundworm that can survive and multiply in the human digestive tract.

They can mature to adulthood, live for one to two years, and produce many eggs inside human intestines.

In contrast, porcine whipworm and rat tapeworm typically don’t survive to adulthood in humans.

This means that people who self-treat with porcine whipworm and rat tapeworm have to take regular doses to maintain a population in their system.

On the upside, those species are less likely to multiply out of control and produce symptoms of infection.

“The porcine whipworm and the rat tapeworm are the two that don’t live in people for very long, so you have to keep taking those over and over again,” Parker explained. “But those are the most popular ones, I think because they have less adverse side effects than the other worms, which do live inside people.”

In their 2015 study, Parker and his colleagues found that self-treaters were more likely to report benefits from helminth therapy than adverse side effects.

“What we see is a ratio of very good response to very bad response of probably about 25 or 30 to 1,” Parker said.

When adverse side effects were reported, they included fatigue, skin rashes, and mild to severe gastrointestinal problems.

People who experience severe side effects can remove helminths from their bodies using antihelminthic drugs.

While helminth therapy might strike some people as a fad, it’s not without scientific basis.

“The idea is that humans have evolved with parasitic worms, and during the course of this evolution, the parasitic worms have had an effect on the human immune system,” Harnett told Healthline.

Modern technologies and lifestyles have contributed to the depletion of the human biome, including the loss of helminths from many human bodies.

This loss of internal biodiversity may have contributed to the rise of allergic and autoimmune conditions in developed countries.

In animal studies involving mice, investigators have found that exposure to helminths provides protective effects against many of those diseases, such as inflammatory bowel disease, multiple sclerosis, and asthma.

“Almost any worm species that has been tested, in almost any animal model of immunity, autoimmunity, or allergy, has given positive data,” Harnett said.

Despite these findings, helminth therapy is unlikely to go mainstream any time soon.

In a profit-driven system where drug companies provide much of the funding for human clinical trials, it’s challenging to obtain much-needed financial support.

“Our current system of drug development is based around pharmaceuticals,” Parker said. “It holds great promise for profits if you get a drug through that system, but if you’re looking at a naturally occurring worm, there’s not a lot of intellectual property. Who’s going to spend millions of dollars getting that tested, when there’s no giant pot of gold at the end of the rainbow?”

As a result of regulatory and financial hurdles, few human clinical trials have been conducted.

Among those that have, the findings have been disappointing.

“There was a lot of early promise, but the situation in human clinical trials hasn’t been as successful,” Harnett said.

“They’ve found that humans seem to tolerate the worms, at least in the numbers employed in the clinical trials, pretty well,” he continued. “So there doesn’t seem to be a safety issue, but there are issues of efficacy.”

Parker attributed some of those issues to the technical challenges of formulating helminths for clinical trials.

Parker does remain hopeful for the future of helminth therapy.

“I think eventually, we’ll understand that helminths are just a normal part of the ecosystem of our body. And eventually, I think it’s going to go beyond just a therapy. I think it’ll be a kind of probiotic that people will be using just to maintain health.”

Rather than treatment with live worms, some believe the future of helminth therapy lies in helminth-derived molecules and synthetic analogues.

Harnett’s research suggests that some molecules derived from the secretions and excretions of helminths provide similar protective effects as live worms.

In the meantime, people who are interested in trying helminth therapy should thoroughly research the potential benefits and risks, Parker advised.

If they decide to self-treat, they should do so under the supervision of a doctor, even if that doctor is unable or unwilling to recommend helminth therapy.