Used medicinally by Native Americans, goldenseal has an active compound called berberine, which has demonstrated powerful antimicrobial action in lab studies (though it's not easily absorbed). University of Illinois researchers found that goldenseal inhibits the growth of H. pylori, the bacterium behind most ulcers. Other studies indicate its value in treating giardiasis and infectious diarrhea. Goldenseal causes no significant side effects, though long-term use can be expensive. Many herbalists recommend it only for symptoms of persistent intestinal distress. Take 2 to 4 mL tincture or 0.3 to 1 mL fluid extract.