Proposed Web Version

The Flu, the Common Cold, and
Complementary Health Practices
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.
© BananaStock/Thinkstock

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.
To prevent or treat these illnesses, some people turn to
complementary health practices. This fact sheet summarizes “what
the science says” about some of these practices and suggests
sources for additional information. If you are considering using a
complementary health practice 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 practices for the flu. There is no
conclusive evidence that any complementary health practice is
useful for the flu.

•

Complementary health practices for colds. There is scientific
evidence about several complementary health practices 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 overthe-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.

•

Tell all your health care providers about any complementary health practices 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 Practices 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:
•
•
•

Flu.gov, the Federal Government’s one-stop online resource on the flu
The MedlinePlus page on the flu, from the National Library of Medicine
(www.nlm.nih.gov/medlineplus/flu.html)
Understanding Flu, from the National Institute of Allergy and Infectious Diseases
(www.niaid.nih.gov/topics/Flu/understandingFlu/Pages/default.aspx).

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

2

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 Practices for the Flu
Although a few studies suggest a potential role for some complementary therapies, there is no
strong scientific evidence that any complementary health practice is useful against the flu.
Examples of complementary health practices 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 Practices 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:
•
•

The MedlinePlus page on colds (www.nlm.nih.gov/medlineplus/commoncold.html)
Understanding the Common Cold, from the National Institute of Allergy and Infectious
Diseases (www.niaid.nih.gov/topics/commonCold/Pages/default.aspx).

Use of Complementary Health Practices for Colds
According to the 2007 NHIS, colds were the eighth most common reason for using
complementary health practices among adults and the third most common among children.

3

What the Science Says About Complementary Health Practices for Colds
•

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.
o

o

o

•

About Scientific Evidence on
Complementary Health Practices
Scientific evidence on
complementary health practices
includes results from laboratory
research (e.g., animal studies) as
well as clinical trials (studies in
people). It provides information on
whether a practice 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 Alternative Medicine (NCCAM)—
like this one—base information
about research findings primarily on
the most rigorous review articles,
known as systematic reviews and
meta-analyses.

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 U.S. Food and Drug Administration 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.
o

o

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.

4

•

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.
o

o

o

•

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 NCCAM-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.
o

o

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 practices
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.
5

NCCAM-Funded Research
NCCAM-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 Practice for the Flu or Colds
•

Do not use any complementary health practice as a substitute for vaccination against the flu.

•

Do not use unproven therapies as a replacement for conventional medical care or as a
reason 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 NCCAM fact sheet Using Dietary Supplements
Wisely at nccam.nih.gov/health/supplements/wiseuse.htm.

•

Tell all your health care providers about any complementary health practices you use. Give
them a full picture of what you do to manage your health. This will help ensure
coordinated and safe care. For tips about talking with your health care providers about
complementary and alternative medicine, see NCCAM’s Time to Talk campaign at
nccam.nih.gov/timetotalk/.

Selected References
Barrett B, Brown R, Rakel D, et al. Echinacea for treating the common cold: a randomized trial. Annals of Internal
Medicine. 2010;153(12):769-777.
Bukutu C, Le C, Vohra S. Complementary, holistic, and integrative medicine: the common cold. Pediatrics in Review.
2008;29(12):e66-e71.
Chen XY, Wu T, Liu GJ, et al. Chinese medicinal herbs for influenza. Cochrane Database of Systematic Reviews.
2007;(4):CD004559 [edited 2010]. Accessed at http://www.thecochranelibrary.com on December 12, 2011.
Davidson TM, Smith WM. The Bradford Hill criteria and zinc-induced anosmia: a causality analysis. Archives of
Otolaryngology—Head & Neck Surgery. 2010;136(7):673-676.
Eccles R, Weber O, eds. Common Cold. Basel, Switzerland: Birkhäuser; 2009.
Guo R, Pittler MH, Ernst E. Complementary medicine for treating or preventing influenza or influenza-like illness.
American Journal of Medicine. 2007;120(11):923-929.

6

Hao Q, Lu Z, Dong BR, et al. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database of
Systematic Reviews. 2011;(9):CD006895. Accessed at http://www.thecochranelibrary.com on January 3, 2012.
Hemilä H, Chalker E, Douglas B. Vitamin C for preventing and treating the common cold. Cochrane Database of
Systematic Reviews. 2007;(3):CD000980 [edited 2010]. Accessed at http://www.thecochranelibrary.com on
December 12, 2011.
Hempel S, Newberry S, Ruelaz A, et al. Safety of Probiotics to Reduce Risk and Prevent or Treat Disease. Evidence
Report/Technology Assessment no. 200. Agency for Healthcare Research and Quality Web site. Accessed at
http://www.ahrq.gov/clinic/tp/probiotictp.htm on January 27, 2012.
Kassel JC, King D, Spurling GKP. Saline nasal irrigation for acute upper respiratory tract infections. Cochrane Database of
Systematic Reviews. 2010;(3):CD006821. Accessed at http://www.thecochranelibrary.com on December 11, 2011.
Linde K, Barrett B, Bauer R, et al. Echinacea for preventing and treating the common cold. Cochrane Database of
Systematic Reviews. 2006;(1):CD000530 [edited 2009]. Accessed at http://www.thecochranelibrary.com on
December 12, 2011.
Lissiman E, Bhasale AL, Cohen M. Garlic for the common cold. Cochrane Database of Systematic Reviews.
2009;(3):CD006206. Accessed at http://www.thecochranelibrary.com on December 12, 2011.
Office of Dietary Supplements. Dietary Supplement Fact Sheet: Zinc. Office of Dietary Supplements Web site. Accessed at
http://ods.od.nih.gov/factsheets/Zinc-HealthProfessional on December 1, 2011.
Public health advisory: loss of sense of smell with intranasal cold remedies containing zinc. June 16, 2009. U.S. Food
and Drug Administration Web site. Accessed at www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafety
InformationforPatientsandProviders/DrugSafetyInformationforHeathcareProfessionals/PublicHealthAdvisories/
ucm166059.htm on January 7, 2012.
Roxas M, Jurenka J. Colds and influenza: a review of diagnosis and conventional, botanical, and nutritional
considerations. Alternative Medicine Review. 2007;12(1):25-48.
Schoop R, Klein P, Suter A, et al. Echinacea in the prevention of induced rhinovirus colds: a meta-analysis. Clinical
Therapeutics. 2006;28(2):174-183.
Shah SA, Sander S, White CM, et al. Evaluation of echinacea for the prevention and treatment of the common cold: a
meta-analysis. Lancet Infectious Diseases. 2007;7(7):473-480.
Singh M, Das RR. Zinc for the common cold. Cochrane Database of Systematic Reviews. 2011;(2):CD001364. Accessed at
http://www.thecochranelibrary.com on December 12, 2011.
Woelkart K, Linde K, Bauer R. Echinacea for preventing and treating the common cold. Planta Medica. 2008;74(6):633-637.
Yamshchikov AV, Desai NS, Blumberg HM, et al. Vitamin D for treatment and prevention of infectious diseases: a
systematic review of randomized controlled trials. Endocrine Practice. 2009;15(5):438-449.
Zhang X, Wu T, Zhang J, et al. Chinese medicinal herbs for the common cold. Cochrane Database of Systematic Reviews.
2007;(1):CD004782 [edited 2010]. Accessed at http://www.thecochranelibrary.com on December 12, 2011.

7

For More Information
NCCAM Clearinghouse
The NCCAM Clearinghouse provides information on NCCAM and complementary health
practices, 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.: 1-888-644-6226
TTY (for deaf and hard-of-hearing callers): 1-866-464-3615
Web site: nccam.nih.gov
E-mail: [email protected]

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.
Web site: www.niaid.nih.gov/
Toll-free in the U.S.: 1-866-284-4107

Flu.gov
Managed by the U.S. Department of Health and Human Services, Flu.gov provides
comprehensive Government-wide information on seasonal, H1N1 (swine), H5N1 (bird), and
pandemic influenza for the general public, health professionals, and others.
Web site: www.flu.gov

PubMed®
A service of the National Library of Medicine, PubMed contains publication information and (in
most cases) brief summaries of articles from scientific and medical journals.
Web site: www.ncbi.nlm.nih.gov/sites/entrez

MedlinePlus
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.
Web site: www.medlineplus.gov
Information on the common cold: www.nlm.nih.gov/medlineplus/commoncold.html
Information on flu: www.nlm.nih.gov/medlineplus/flu.html

8

Acknowledgements
NCCAM thanks Linda Duffy, Ph.D.; Wendy Weber, N.D., Ph.D., M.P.H.; and Jack Killen, M.D.,
NCCAM, 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.
NCCAM 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 NCCAM.
National Institutes of Health
♦♦♦
U.S. Department of Health and Human Services

9

D444
Created January 2010
Updated February 2012