Antibiotics can lower the amount of flora in the large intestine. This can use "bad" pathogenic bacteria to manifest causing infections. Reducing the number of flora can lower the amount of metabolites and carbohydrates are taken up by the body. The function of the flora to maintain a balance of hormones and carbohydrates in your body. They also fend off harmful bacteria and produce essential vitamins. With flora, humans can not survive. Antibiotics have adverse effects on the flora in the large intestine.