At my first M and M as a medical student, I heard the story of a patient who had received antibiotics for an upper respiratory tract infection.

CNN: More is not always better in medicine

In CIC clinical trials, the most common side effect were diarrhea (16% vs 5% placebo), abdominal pain (7% vs 6%), flatulence (6% vs 5%), upper respiratory tract infection (5% vs 4%), sinusitis (3% vs 2%) and abdominal distension (3% vs 2%).

FORBES: FDA Approves New Drug For Irritable Bowel Disorder (Update)