I've taken a prescription probiotic, "Flora Q". It didn't help my constipation, but I felt better. Before the Flora Q, my legs & arms felt like jelly, & I was tired all the time. I feel more sickly without hte Flor Q. I had attended a screening for a Phase II clinical trial for Mitemcinal Fumarate, (for IBS-C), in February. The coordinator gave me the breath test for bacteria in my small intestine, & it indicated that I had none, (even though I'm severely constipated). When she called the doctor at the pharmaceutical company, (who was supervising the trial), he told her that a probiotic is more potent than an antibiotic. He said I would have to be off the probiotic for 3 months to be considered again for the trial. The irony is that the screening questions had a lot of questions about taking antibiotics recently, & no questions about probiotics. So, Flora Q does wipe out the bacteria in your smaill intestine.