Berberine is the main alkaloid found in barberry. Research published in the Journal of Infectious Disease (1987 May;155(5):979-984) looked at its efficacy of berberine in treating diarrhea caused by bacteria. The subjects were 165 patients suffering from diarrhea caused by either Escherichia coli or Vibrio cholera. They were randomly divided into two groups. One group received a single dose 400 mg of berberine sulfate; the other group acted as a control. For patients with diarrhea caused by Escherichia coli there was significant reduction in the amount of stool produced in the test group when compared to the controls. After 24 hours, 42% of the berberine group stopped having diarrhea, as compared to 20% of the controls.

For the patients with diarrhea caused by Vibrio cholera, the group receiving the berberine had a reduction in stool volume. However, patients with cholera who received 1200mg of berberine sulfate plus tetracycline did not have significant reduction in stool output compared with patients who received tetracycline alone.