The Herb Research Foundation: Herb Information Greenpaper


Doctors and nutritionists have long known that zinc is needed by the human body for optimal well-being, especially for maintaining a healthy immune system. Now, promising scientific research demonstrates that zinc offers an effective treatment for the common cold. In fact, studies show that zinc can cut the duration of cold symptoms by about half. Although zinc may not work for everyone, thousands of Americans have come to rely on zinc lozenges to speed recovery during cold and flu season.

Primary uses of Zinc


Zinc is recognized as an essential mineral for maintaining a healthy immune system and a variety of other important body processes. These include protein synthesis and cell growth, tissue growth and repair, enzymatic reactions, and the proper function of hormones such as insulin and sex and growth hormones. Zinc is necessary for the prevention of infections, wound healing, sexual development and function (especially for males), bone growth, and the senses of vision, taste, and smell. Zinc also helps the body utilize vitamins, such as E and A.

The adult US RDA for zinc -- the amount recommended by researchers for maintaining health -- is 12 mg a day for women and 15 mg a day for men. Although zinc is found in many different foods, low levels may be seen in people with certain health conditions and in those with poor diets, such as some elderly people. Some signs of zinc deficiency are frequent infections, slow wound healing, lack of appetite, loss of senses of taste or smell, skin problems, and impotence. Good food sources of zinc include fish, oysters, whole grains, legumes, nuts, and seeds, especially pumpkin seeds.

Health Benefits of Zinc

In addition to the immune-boosting and cold-fighting properties of zinc, research has revealed that it has antioxidant properties. Antioxidants are believed to help the body maintain its defenses against cell damage that is implicated in aging as well as cancer and other serious diseases. Zinc has also shown potential in the treatment of disorders such as prostatitis (inflammation of the prostate gland) and recurrent herpes infections.

Perhaps most interesting for the millions who get colds each year is the discovery that zinc is an effective treatment for the common cold. In a number of clinical studies, zinc (in the form of zinc gluconate) significantly shortened the length of time people suffered from cold symptoms, including headache, congestion, runny nose, sore throat, coughing, and hoarseness. Laboratory studies (in vitro) show that zinc interferes with the reproduction of viruses known to cause colds, such as rhinoviruses and herpes simplex viruses. On the other hand, some clinical studies have reported that zinc is ineffective in treating symptoms of the common cold.

State of Knowledge

Clinical (human) research
Laboratory research
History of use / Traditional use
Safety record
International acceptance

Stars indicate level of knowledge on a scale from 0 - 5

Research Findings

A number of well-controlled clinical trials support the use of zinc lozenges for the treatment of colds. These studies were placebo-controlled and double-blind, meaning that the zinc lozenges were tested for effectiveness against an inactive substance (placebo) and that neither the researchers nor the study participants knew who received which substance until the end of the study. Listed below are a number of clinical studies that demonstrated the effectiveness of zinc against colds as well as two that showed it is ineffective.

Specific Studies:

Clinical Study: In a placebo-controlled study involving 100 volunteers, cold symptoms lasted only 4.4 days for people taking 13.3 mg of zinc every two hours, as compared to 7.6 days for those taking placebo (Mossad, et al. 1996)

Clinical Study: Results of this double-blind, placebo-controlled study showed that 86% of 37 people who took zinc tablets reported that their cold symptoms were gone in seven days, compared to only 46% of the 28 people who took placebo. The dosage of zinc was 23 mg every two hours (Eby, et al. 1984).

Clinical Study: In 35 people who began treatment with zinc lozenges one day after cold symptoms began, the duration of symptoms was 4.3 days, as compared to 9.2 days for the 38 who took placebo. Zinc dosage was 23.7 mg taken at two hour intervals (Godfrey, et al. 1992).

Clinical study: Results of two studies involving a total of 77 people showed that zinc gluconate lozenges were ineffective in reducing the duration or severity of cold symptoms (Farr, et al. 1987).

Results of human studies: Significantly reduces the duration of symptoms of the common cold. Anecdotal reports as well as the results of one study suggest that the sooner the zinc treatment is started, the sooner cold symptoms improve.

Laboratory Study: Inhibits the reproduction of viruses known to cause colds.


At recommended dosages, zinc is generally well tolerated by most people. The most common side effects reported in the clinical trials using zinc lozenges for colds were unpleasant taste, minor mouth irritation, and gastrointestinal upset such as nausea and/or vomiting.

Using Zinc

Zinc is most commonly available in the form of tablets and lozenges. In tablet form, zinc may be supplied alone or in combination with other supplements as part of a multivitamin or multimineral formula. Most zinc supplements combine pure (or elemental) zinc with another compound. Examples include zinc acetate, zinc gluconate, and zinc picolinate.

Important Note:

Taking more than 100 mg a day of zinc for extended periods of time could result in problems such as depressed immune function and imbalances in levels of copper. The use of high doses of zinc for longer than seven days at a time is not recommended.

This page and all contents are © 1997 by The Herb Research Foundation, Boulder, CO, USA.