Can antibiotics change the color of your stool to a dark brown?

Yes: About one third of the solid matter in stool is dead bacteria. Also, the actions of bacteria on bilirubin influences the color of stool. We have trillions of bacteria in our intestines and antibiotics kill many of these bacteria, influencing the color of our stool. I advise taking probiotic supplements both during and after taking antibiotics to restore our normal intestinal flora.