Patients who are over-prescribed antibiotics may develop drug resistance that lasts up to a year. This puts both them and the larger population at risk.
The more antibiotics are prescribed for coughs and flu-like illnesses, the more bacteria become resistant in a vicious cycle.
According to Reuters:
"Medical experts say overuse of antibiotics in Europe, the United States and other wealthy regions is building widespread resistance in and threatening vital medical treatments from hip replacements and cancer therapies, to intensive care."