Recent studies have revealed that the conditions of intestinal bacteria are associated with the functions in the brain. The patients with depression or autism have a deteriorated intestinal balance. During an animal study, laboratory mice that were administrated with antibiotics demonstrated an aggravated gut microbiota, and a drop of the levels of beneficial substances which were generated by intestinal bacteria. The blood concentration of corticosterone which is known as a stress hormone increased. Moreover, the deteriorated conditions in the amygdala and hippocampus in the brain were observed. It drove changes in substances responsible for neural transmission to the cerebrum resulted in causing negative impacts in their memory and ability to learn.

In light of these circumstances, the World Health Organization made calls in 2015 about the proper use of antibiotics. What we should not forget is the fact that antibiotics are absolutely necessary to save lives. If we stop demanding antibiotics without careful consideration, the speed of widespread of antibiotic-resistant bacteria will slow down. It will make antibiotics more effective when it is truly needed.