In every person there are billions of microorganisms that keep your gut (intestines) working properly. Some medicines, certain diseases, travel and stress can cause an upset in the balance of microorganisms in your body. Florastor® helps maintain the balance in your intestines and is safe to take with other medicines.† What is Florastor®? Florastor® is a probiotic made of live freeze dried yeast cells of the species Saccharomyces boulardii. The cells are put into capsules and sealed. Each capsule of Florastor® has 250 mg of S. boulardii in it.