Antibiotics are drugs that kill bacteria. They are effective against bacteria only and have no effect on viruses. Therefore, antibiotics will not cure the common cold, flu, or any other viral illness. Unless you have a bacterial infection, it's best to avoid the possible adverse effects of antibiotics, which may include:

• Side effects, including allergic reactions. Common side effects of antibiotics include nausea, diarrhea, and increased sensitivity to sunlight. Most side effects are mild, but some, especially allergic reactions, can be severe. A severe allergic reaction usually causes shortness of breath and can be life-threatening. If you have any unexpected reaction to an antibiotic, tell your health professional before another antibiotic is prescribed.
• Secondary infections. Antibiotics kill most of the bacteria in your body that are sensitive to them, including the bacteria that help your body. Antibiotics can destroy the bacterial balance in your body, leading to stomach upset, diarrhea, vaginal infections, or other problems.
• Bacterial resistance. When antibiotics are used too often, bacteria change so that the antibiotics are no longer effective against them. This makes bacterial infections more difficult to treat.

When you and your health professional have decided that an antibiotic is necessary, carefully follow the instructions for taking the prescription.

• Take the whole dose for as many days as prescribed, unless you have unexpected side effects (in which case, call your health professional). Antibiotics kill off many bacteria quite quickly, so you may feel better in a few days. However, if you stop taking the antibiotic too soon, the weaker bacteria will have been eliminated, but the stronger ones may survive and multiply.
• Be sure you understand any special instructions for taking the medication. The instructions should be printed on the label, but double-check with your doctor and pharmacist.
• Store antibiotics in a cool, dry place. Check carefully to see if they need refrigeration.
• Never give an antibiotic prescribed for one person to someone else.
• Do not save leftover antibiotics, and do not take an antibiotic prescribed for another illness without a health professional's approval.