The most adverse effect of antibiotic overuse is antibiotic resistance. This means bacteria become resistant to the effects of antibiotics, resulting in bacterial infections that cannot be cured by the same antibiotic. According to the United States Centers for Disease Control and Prevention (CDC), antibiotic resistance is one of the most serious public health threats the world faces.
Antibiotics effectively treat bacterial infections, but are of no use against viral infections such as those that cause colds. When patients take antibiotics for the wrong diseases, it can result in antibiotic-resistant bacteria that require stronger and often more expensive drugs to treat. Eventually, the rise of these "super bacteria" can result in fatal infections that cannot be treated by any known antibiotic. Antibiotics also target all kinds of bacteria, resulting in the death of useful bacteria in the stomach.
The CDC recommends avoiding antibiotics when possible. When a doctor prescribes an antibiotic, ensure that doses are not skipped. The use of specific antibiotics instead of broad-spectrum types can also reduce the development of antibiotic-resistant bacteria, but may require additional time as a culture test is necessary. For example, the use of drops for an ear infection targets the bacteria responsible for the infection and does not affect other bacteria in the body.