Antibiotics are the keystone of contemporary medicine, but their overuse can generate unwanted side effects, HealthLine reports.

The U.S. Centers for Disease Control and Prevention (CDC) isn’t historically known for using pessimistic language, but lately they’ve been sounding the alarms about the consequences of overusing antibiotics.

CDC director Tom Frieden has warned of “nightmare bacteria,” those that have evolved defenses against modern antibiotics. This leads to strains that can cause fatal infections.

1. Antibiotics Increase Fatal Diarrhea Cases in Children

Because the majority of common colds are viral, using antibiotics to treat them does nothing to stop the infection and can create unwanted side effects.

A new CDC study shows that children given antibiotics for routine upper respiratory infections are more susceptible to aggressive antibiotic-resistant strains of the bacteria that can cause severe diarrhea and is responsible for 250,000 infections in hospitalized patients and 14,000 deaths every year among children and adults.

2. Antibiotics Can Upset Sensitive Gut Flora

Your intestines contain around 100 trillion bacteria of various strains. While some can be deadly, there’s a natural balance in the gut that can be thrown out of whack by antibiotics. These helpful bacteria, known as gut flora, support immunity and proper digestion.

Aggressive antibiotics, while helpful if you have a serious infection, can wipe out many good gut bacteria while leaving those immune to antibiotics to flourish. 

3. Antibiotics Are Increasing Cases of Untreatable Gonorrhea

CDC is aggressively tracking cases of antibiotic-resistant gonorrhea. This untreatable gonorrhea not only causes pain but also has been linked to pelvic inflammatory disease, ectopic pregnancy, tubal infertility, and neonatal eye infections, among other conditions.