Before the discovery that essential symbiotic bacteria live in and on us, antibiotics were viewed largely as innocuous. As the “gut microbiome” (the microorganisms living in the intestines) becomes better understood, so too do the deleterious effects that antibiotics exert on our health. One immediate effect, as many people who have taken antibiotics know, is the “good bacteria” can be killed off in the gut.
The short-term consequence can be diarrhea. The long-term consequences are still being uncovered. 
We do know there are several possible effects of antibiotics. A study published in the journal Frontiers in Cellular and Infection Microbiology in 2020 found that antibiotic use is linked to obesity, gastrointestinal infections, inflammatory bowel disease, and even colorectal cancer. Early antibiotic exposure is also linked to “childhood asthma, allergies, and airway illnesses,” the researchers wrote.
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