It's official: Antibiotics do more harm than good for people with common colds.

That's true even if you have what doctors call "purulent rhinitis" -- what kids call "green snot."

Antibiotics are great for bacterial infections. Unfortunately, viruses cause nearly all colds. Viruses don't mind if you take antibiotics, but your body does. Diarrhea is the most common side effect.

Doctors used to give antibiotics to people with colds, hoping they would prevent bacteria from infecting people when they were already ill. But that doesn't really work, according to an exhaustive review of the medical literature.

"Antibiotics appear to have no benefit in the treatment of acute upper respiratory tract infections," write Bruce Arroll, MBChB, PhD, and Timothy Kenealy, MBChB, of the University of Auckland in New Zealand.

"The implications for practice are that prescription of antibiotics should not be given in the first instance as they will not improve the symptoms and adult patients will get adverse effects."

Read WebMD's "Understanding Common Cold -- Prevention"

What About Green Snot?

Arroll and Kenealy note that antibiotics can help some people with purulent rhinitis/green snot. But the odds are against it. The chance antibiotics might help is somewhere between 4 to 1 and 8 to 1.

Even if you think the intestinal side effects are worth that chance, another factor makes it a bad bet. That fact: Overuse of antibiotics breeds drug-resistant super germs. That means there may come a day when antibiotics don't work -- not just for colds but for deadly illnesses.

So what does help?

"Patients will get a quicker fix if they take decongestants such as Sudafed," Arroll says in a news release.

What about chest colds? Antibiotics don't help there, either -- even if you're coughing up ugly green phlegm.

Read WebMD's "Time, Not Antibiotics, Best Rx for Chest Cold"

By Daniel J. DeNoon, reviewed by Michael W. Smith, MD

SOURCES: Arroll, B. and Kenealy, T. The Cochrane Library, 2005. News release, Health Behavior News Service.