Diagnosis: The Cold Hard Truth

The common cold and flu have everyone searching for elixirs. Here's the lowdown on five popular remedies:

AHCC

What is it?

Active Hexose Correlated Compound is a nutritional supplement derived from mushrooms.

Efficacy

In a 2006 study, it boosted natural killer cell activity and reduced the severity of flu in mice.

Side effects

A minority of users may experience nausea, diarrhea, headache, or fatigue.

Airborne

What is it?

A popular herbal health concoction. Its claim that it prevents and treats colds and flus came under attack, resulting in a $23.3 million settlement.

Efficacy

No peer-reviewed studies have demonstrated its effectiveness.

Side effects

The high concentrations of vitamins C and A may be dangerous for pregnant women.

Echinacea

What is it?

Echinacea, or the purple coneflower, is a perennial plant long used in herbal medicines.

Efficacy

There's some evidence it decreases the severity of colds if used just as a cold is coming on.

Side effects

Some allergy risks and possible interference with drugs that treat asthma and diabetes.

Vitamin C

What is it?

Perhaps the best-known essential nutrient. Its medicinal properties, however, are controversial.

Efficacy

A 2007 meta-analysis concludes that it has no effect on illness.

Side effects

High doses may lead to indigestion, diarrhea, stomach inflammation, or even kidney stones.

Zinc

What is it?

An essential trace element sold as a cold remedy in the form of lozenges, nasal sprays, and gels.

Efficacy

Mixed results. One meta-analysis found it to be ineffective, but doses and preparations vary.

Side effects

Bad taste and mouth irritation. More rarely: nausea, diarrhea, anemia, or even damage to one's sense of smell.