5 supplements that may make IBS worse

By Elizabeth Pratt | Fact-checked by Davi Sherman
Published April 24, 2025

Key Takeaways

Industry Buzz

  • “[The] problem of probiotics is [that] the[y] are not controlled by any agency.” — Ashkan Farhadi, MD

When it comes to irritable bowel syndrome (IBS), not all supplements are created equal. While some studies suggest that certain supplements may play a role in IBS management, other supplements may make symptoms worse. []

MDLinx took a deep dive into some supplements that may not benefit individuals with IBS—or that might just be a waste of money.

Cheap probiotics

Research suggests that some probiotics might be beneficial for individuals with IBS, while others may not make a difference. []

“[The] problem of probiotics is [that] the[y] are not controlled by any agency. Basically, whatever [manufacturers] like to claim, they would, because that is considered a food supplement, and when it's a food they cannot verify whatever they claim is accurate," says Ashkan Farhadi, MD, a board-certified gastroenterologist and director of the Digestive Disease Center at MemorialCare Medical Group in Orange County, CA, and the author of “The Rhymes of Happiness: Weaving Science, Art and Poetry in the Pursuit of Happiness.”

For example, if a manufacturer says there's 10 billion bacteria in a probiotic, who knows if one of those bacteria are alive, and if any of those even get to the gut—even if they are alive in that capsule—no one really knows, Dr. Farhadi explains.

“We only have a few of them [probiotics] that are proven to be effective, particularly in IBS, and those are the most expensive ones. People usually go for the cheaper one, and I don't blame them, because [they’re] really pricey,” Dr. Farhadi adds.

Related: 5 supplements you should be taking—and when

Some fiber supplements

While some fiber supplements might be beneficial for people with IBS, certain supplements may worsen IBS symptoms. []

Some fiber supplements are highly fermented and may cause pain, discomfort, bloating, diarrhea, and excessive gas. This can occur in patients with and without IBS.

For patients with IBS, fiber supplements that have high FODMAP content may not be suitable. High-FODMAP fiber supplements include wheat bran, fructooligosaccharides, and inulin-based products.

Calcium

While calcium supplements can benefit bone health, they can cause gastrointestinal (GI) upset in some individuals. [] Calcium supplements can cause constipation, gas, and bloating in some people.

Iron

People with iron deficiency may need to take iron supplements. When taken at high doses, especially on an empty stomach, these supplements can cause a variety of GI symptoms. []

These symptoms include constipation, nausea, abdominal pain, diarrhea, and vomiting.

The daily upper limit for iron from all sources—food, supplements, and drinks—is 45 milligrams for adults.  

Vitamin C

The majority of people in the United States get enough vitamin C through their diet. But vitamin C supplements are available, and they can cause GI symptoms if taken at high doses. []

Too much vitamin C can cause stomach cramps, nausea, and diarrhea.

The daily upper limits for vitamin C from all sources—supplements, food, and drinks—is 2,000 milligrams for adults.

Related: 4 longevity supplements that actually do more harm than good
Share with emailShare to FacebookShare to LinkedInShare to Twitter
ADVERTISEMENT