Consumers have gone crazy for probiotics.

They get them through food (such as yogurt), beverages and dietary supplements.

According to the National Institutes of Health, preliminary evidence exists that some probiotics may help prevent diarrhea caused by infections or antibiotics, and may help ease symptoms of irritable bowel syndrome, but those beneficial effects have not yet been demonstrated conclusively. Scientists still don’t know which probiotics are helpful, or how much someone would need to take in order to benefit from them.

Dr. Andreas Stefan, chief of the Division of Gastroenterology at Maine Medical Center, agrees with that assessment. For some conditions, probiotics have been shown to be effective, he said, “but they’re pretty particular.”

“I do suggest probiotics for some folks, and I do prescribe them in some instances with good data to support it, but that data is iffy in most things,” Stefan said.

Stefan points out that products containing probiotics can be expensive, so consumers must decide whether they’re worth the money when there is no guarantee they will work. “They may or may not help,” he said. “They typically don’t hurt.”