Colds and flus are NOT cured by antibiotics.
Antibiotics - colds and flu
Antibiotics can destroy normal ("healthy") bacteria that live in your body. This can result in symptoms such as nausea, diarrhea, and vaginal yeast infections.
The overuse of antibiotics has played a role in the rise in drug-resistant bacterial infections. Taking antibiotics also poses a risk of allergic reaction, so they should not be taken when there is no possible benefit.
Anon JB. Upper Respiratory Infections. American Journal of Medicine. April 2010;123(4):suppl 1.
Lindell A, Kelsberg G, Safranek S. Antibiotics for viral upper respiratory tractinfections in children. Am Fam Physician. 2011;83(6):747-752.