National Center for Complementary and Integrative Health (NCCIH)

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The Flu, the Common Cold, and Complementary Health Approaches

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The flu (influenza) and the common cold are diseases of the respiratory tract, which includes the nose, throat, breathing passages, and lungs. The two diseases have some symptoms in common, and both are caused by viruses. However, they are different conditions, and the flu is more dangerous. Colds generally do not cause serious complications, such as pneumonia, or lead to hospitalization; the flu sometimes does.

Each year, an estimated 5 to 20 percent of Americans come down with the flu. The number of deaths from the flu and its complications varies from year to year, ranging from a low of 3,000 to a high of 49,000 deaths annually. Vaccination is the best protection against getting the flu.

The common cold is among the leading reasons for visiting a doctor and for missing school or work. More than 200 different viruses can cause colds.

Some people use complementary health approaches for the flu or colds. This fact sheet summarizes what the science says about some of these approaches and suggests sources for additional information. If you are considering using a complementary health approach for the flu or a cold, this information can help you talk to your health care provider about it.


Key Points

  • Vaccination is the best protection against getting the flu.
  • Complementary health approaches for the flu. There is no conclusive evidence that any complementary health approach is useful for the flu.
  • Complementary health approaches for colds. There is scientific evidence about several complementary health approaches for colds. Zinc taken orally (by mouth) may reduce the length and severity of a cold. For most people, taking vitamin C supplements on a regular basis only slightly reduces the length and severity of colds and does not reduce the number of colds that they catch. Despite much research, echinacea has not been proven to prevent colds or relieve their symptoms. There is weak evidence that probiotics might help to prevent colds.
  • Keep in mind that “natural” does not always mean “safe”; some complementary health products derived from natural sources may interact with medications (prescription or over-the-counter) or other natural products, some may have side effects on their own, and some may be unsafe for people with specific medical problems.
  • Intranasal (taken through the nose) zinc products for colds can cause a long-lasting, possibly permanent, loss of the sense of smell.
  • People can get infections if they use neti pots or other nasal rinsing devices improperly. The U.S. Food and Drug Administration (FDA) has information on how to use these devices safely.
  • Tell all your health care providers about any complementary health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.


Complementary Health Approaches and the Flu

About the Flu

The flu is a respiratory infection caused by a number of viruses. Symptoms come on suddenly and are worse than those of colds; they may include body or muscle aches, chills, and fever, as well as cold-like symptoms such as cough and sore throat. The flu can cause serious complications, especially in very young children, elderly people, pregnant women, and people with chronic medical problems, such as asthma, diabetes, or heart disease. Although everyday steps to prevent the spread of germs—such as frequent hand washing and avoiding contact with sick people—can help to prevent the spread of flu, annual flu vaccination is the single best method of prevention.

See the following resources for more information about the flu:

Use of Complementary Health Approaches for the Flu

According to the 2007 National Health Interview Survey (NHIS), which included a comprehensive survey on the use of complementary health approaches by Americans, the flu was among the 15 most common reasons for using complementary health approaches among children but was not among the most common reasons among adults.

Protecting Yourself and Your Family Against the Flu

Annual vaccination is the best protection against getting the flu. Starting in 2010, the Federal Government’s Centers for Disease Control and Prevention has recommended annual flu vaccination for all people aged 6 months and older.

What the Science Says About Complementary Health Approaches for the Flu

Although a few studies suggest a potential role for some complementary health approaches, there is no strong scientific evidence that any complementary approach is useful against the flu. Examples of approaches that have been studied for the flu include:

  • Chinese herbal medicines
  • Dehydroepiandrosterone (DHEA)
  • Echinacea
  • Elderberry
  • Green tea
  • N-acetylcysteine (NAC)
  • North American ginseng
  • Oscillococcinum
  • Pomegranate extract
  • Vitamin C
  • Vitamin D.


Complementary Health Approaches and the Common Cold

About the Common Cold

Cold symptoms usually begin 2 or 3 days after you are infected with a cold virus and last 2 to 14 days. Because you can get a cold by inhaling cold viruses or by touching your eyes or nose after you touch surfaces with cold viruses on them, washing your hands and staying away from people who have colds can help you stay healthy.

See the following resources for more information on colds:

Use of Complementary Health Approaches for Colds

According to the 2007 NHIS, colds were the eighth most common reason for using complementary health approaches among adults and the third most common among children.

What the Science Says About Complementary Health Approaches for Colds

About Scientific Evidence on Complementary Health Approaches

Scientific evidence on complementary health approaches includes results from laboratory research as well as clinical trials (studies in people). It provides information on whether an approach is helpful and safe. Scientific journals publish study results, as well as review articles that evaluate the evidence as it accumulates; fact sheets from the National Center for Complementary and Integrative Health (NCCIH)—like this one—base information about research findings primarily on the most rigorous review articles, known as systematic reviews and meta-analyses.

  • Zinc has been used for colds in oral forms (such as lozenges, tablets, or syrup) and intranasal forms (such as swabs or gels). Oral zinc may help to treat colds, but it can cause side effects and interact with medicines. Intranasal zinc has been linked to a severe side effect and should not be used.
    • A 2011 systematic review of 15 clinical trials of oral zinc, involving more than 1,300 people, concluded that zinc helps to reduce the length and severity of the common cold in healthy people when taken within 24 hours after symptoms start. The review also concluded that zinc, taken at low doses for at least 5 months, reduced the number of colds in children. The review did not make a general recommendation for using zinc because different studies used different amounts and forms of zinc. The dose, formulation, and length of use that would be most helpful for colds while producing the fewest side effects have not yet been established.
    • Oral zinc can cause nausea and other gastrointestinal symptoms. Long-term use of zinc, especially in high doses, can cause copper deficiency and may increase the risk of urinary tract problems, reduce immune function, and cause other side effects. Zinc may interact with drugs, including antibiotics and penicillamine (a drug used to treat rheumatoid arthritis).
    • The intranasal use of zinc can cause anosmia (loss of the sense of smell), which may be long-lasting or permanent. In 2009, the FDA warned consumers to stop using several intranasal zinc products marketed as cold remedies because they had been linked to cases of anosmia.
  • For most people, vitamin C does not prevent colds and only slightly reduces their length and severity. Vitamin C is generally considered safe except when taken in high doses.
    • A 2010 systematic review of results from 29 clinical trials involving more than 11,000 people found that taking vitamin C regularly (at least 0.2 grams per day) did not reduce the likelihood of getting a cold but was associated with modest reductions in the length and severity of cold symptoms. However, in five trials in people who were exposed to extreme physical stress (marathon runners, skiers, and soldiers training in subarctic conditions), taking vitamin C cut the number of colds in half. In studies in which people took vitamin C only when they had a cold, the vitamin did not consistently decrease the length or severity of their colds.
    • Vitamin C is generally considered safe; however, high doses can cause digestive disturbances such as diarrhea, nausea, and abdominal cramps.
  • Echinacea has not been proven to help prevent or treat colds. It usually does not cause side effects, but allergic reactions and rashes have been reported.
    • Echinacea products vary widely, containing different echinacea species, plant parts, and preparations. The many clinical trials of echinacea for colds have also varied widely, in terms of products studied, research methods, and study results.
    • Overall, the scientific evidence on echinacea for colds is inconclusive. There is limited evidence that some echinacea preparations might reduce the length or severity of colds in adults, but other preparations did not seem to be helpful. Four NCCIH-funded clinical trials indicated that echinacea did not reduce the length or severity of cold symptoms. In addition, echinacea has not been shown to reduce the number of colds that adults catch. The effects of echinacea in children are uncertain; only a small amount of research has been done in children, and the results of that research are inconsistent. 
    • Few side effects have been reported in clinical trials of echinacea; however, some people may have allergic reactions. In one large clinical trial in children, those who took echinacea had an increased risk of developing rashes.
  • The evidence that probiotics may help to prevent colds is weak, and little is known about their long-term safety.
    • Although a 2011 systematic review of 10 clinical trials involving more than 3,000 people indicated that probiotics might help to prevent upper respiratory tract infections, such as the common cold, the evidence is weak and the results have limitations.
    • As pointed out in a 2011 Agency for Healthcare Research and Quality assessment of the safety of probiotics, little is known about the effects of taking probiotics for long periods of time. It appears that most people can use probiotics without experiencing any side effects—or with only mild gastrointestinal side effects such as gas—but there have been some case reports of serious adverse effects, and the risk of serious side effects may be greater in people with underlying health conditions. Probiotics should not be used by people with serious underlying health problems except with close monitoring by a health care provider. Research on the safety of probiotics is ongoing.

Current evidence does not support recommending certain complementary health approaches that have been investigated for colds, such as:

  • Andrographis (Andrographis paniculata)
  • Astragalus (Astragalus membranaceus)
  • Chinese herbal medicines
  • Elderberry (Sambucus nigra)
  • Garlic (Allium sativum)
  • Green tea
  • Guided imagery
  • Honey
  • Hydrotherapy
  • Nasal irrigation
  • North American ginseng (Panax quinquefolius)
  • Stress management
  • Vitamin E.


Using Neti Pots and Other Nasal Rinsing Devices Safely

Some people use a neti pot or other device to rinse their nasal passages with water when they have a cold. Using these devices improperly can put you at risk of getting a serious infection. The FDA has information on how to use nasal rinsing devices safely.

NCCIH-Funded Research

NCCIH-supported researchers are conducting a variety of studies relevant to the flu and colds. Topics of recent research include:

  • The safety and effectiveness of probiotics and synbiotics (a combination of probiotics and prebiotics) as possible complementary treatments for added immune protection of flu vaccine
  • Meditation and exercise for preventing acute respiratory infection
  • How psychosocial factors, such as the quantity and quality of social relationships, influence the likelihood of catching colds
  • The effects of echinacea on the immune system.


If You Are Considering a Complementary Health Approach for the Flu or Colds

  • Do not use any complementary health approach as a substitute for vaccination against the flu.
  • Do not use unproven therapies to replace conventional medical care or to postpone seeing a health care provider about any medical problem.
  • If you take medications, have serious underlying health problems, or are pregnant or nursing a child, or if you are considering giving a child a dietary supplement or other complementary health product, it is especially important to consult your (or your child’s) health care provider. To learn more, see the NCCIH fact sheet Using Dietary Supplements Wisely.
  • Tell all your health care providers about any complementary health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.


For More Information

NCCIH Clearinghouse

The NCCIH Clearinghouse provides information on NCCIH and complementary and integrative health approaches, including publications and searches of Federal databases of scientific and medical literature. The Clearinghouse does not provide medical advice, treatment recommendations, or referrals to practitioners.

Toll-free in the U.S.: 
TTY (for deaf and hard-of-hearing callers): 

National Institute of Allergy and Infectious Diseases (NIAID)

NIAID conducts and supports research to study the causes of allergic, immunologic, and infectious diseases, and to develop better means of preventing, diagnosing, and treating these illnesses.

Toll-free in the U.S.: 

Managed by the U.S. Department of Health and Human Services, provides comprehensive government-wide information on seasonal, H1N1 (swine), H5N1 (bird), and pandemic influenza for the general public, health professionals, and others.


A service of the National Library of Medicine (NLM), PubMed® contains publication information and (in most cases) brief summaries of articles from scientific and medical journals.


To provide resources that help answer health questions, MedlinePlus (a service of the National Library of Medicine) brings together authoritative information from the National Institutes of Health as well as other Government agencies and health-related organizations.

Information on the common cold
Information on flu


Key References



NCCIH thanks Linda Duffy, Ph.D.; Wendy Weber, N.D., Ph.D., M.P.H.; and John (Jack) Killen, Jr., M.D., NCCIH, for their contributions to the 2012 update of this publication, and Bruce Barrett, M.D., Ph.D., University of Wisconsin Department of Medicine; Sheldon Cohen, Ph.D., Carnegie Mellon University; and Ronald B. Turner, M.D., University of Virginia School of Medicine for their assistance in the development of the original publication.

This publication is not copyrighted and is in the public domain. Duplication is encouraged.

NCCIH has provided this material for your information. It is not intended to substitute for the medical expertise and advice of your primary health care provider. We encourage you to discuss any decisions about treatment or care with your health care provider. The mention of any product, service, or therapy is not an endorsement by NCCIH.

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NCCIH Pub No.: 
Date Created: 
January 2010
Last Updated: 
April 2013