Influenza, or "flu," is a caused by a virus infecting the respiratory system (nose, throat, bronchial tubes, lungs). Flu symptoms are usually more severe than those of the common cold and are more likely to affect other parts of your body. Flu also tends to come on suddenly, while colds can take a while to develop. Flu is very contagious, spreading easily from one person to the next. Most people with healthy immune systems will get over the flu within two weeks, but young children, senior adults, and people with chronic illnesses are more likely to develop complications such as pneumonia. About 35,000 people die of flu each year in the United States.

There are three types of flu viruses: A, B, and C. Type A viruses are the ones responsible for periodic pandemics (worldwide epidemics, such as the one in 1918 that killed as many as 50 million people worldwide). The avian or bird flu is a type A flu virus.

The best way to protect yourself from the flu is to get an annual vaccine (flu shot).

• Fever that comes on suddenly (usually above 101 degrees Fahrenheit)
• Chills and sweats
• Headache
• Muscle or body aches
• Fatigue
• Dry cough
• Sore throat
• Sneezing, runny nose, stuffy nose
• Loss of appetite
• Nausea, vomiting, or diarrhea, especially in children

Influenza is caused by viruses that are spread through the air by sneezes and coughs, or by touching a surface a person with the flu has touched and transmitting the virus to your mouth or nose. Some flu viruses cause a very mild illness, or none at all. Others cause serious, widespread illness.

Since there are many types of influenza virus, and because they change over time, a new flu vaccine is offered every fall. Getting vaccinated before the flu season starts reduces your chances of getting the flu, and helps you recover faster if you do get it. You should not take the vaccine if you have an allergy to eggs, because the viruses for the vaccines are grown in chick embryos. See Risk Factors for list of people who should get the vaccine every year.

Infants and young children, as well as senior adults, are considered at highest risk of complications from flu. Other risks include:

• Having a chronic illness, such as heart disease
• Having a weakened immune system, from medications or HIV
• Pregnant women
• People who work in health care
• People who work in childcare
• Residents of nursing homes

If you are at risk for complications, you should get an annual flu shot (see Prevention).

Your doctor will probably be able to diagnose flu from a physical exam and a description of your symptoms. He or she may take a chest x-ray if there is concern about complications such as pneumonia.

The best way to prevent the flu is by getting a flu shot. Annual flu shots are recommended if you:

• Are 50 or older
• Have chronic heart, lung, or kidney disease
• Live in an institution (such as a nursing home)
• Have a weakened immune system
• Have sickle cell anemia

You should not receive the vaccine if you are allergic to eggs.

You can also cut your risk of flu by washing your hands frequently during flu season.

Bed rest and drinking plenty of fluids are usually enough to treat flu. Mild over-the-counter pain relievers and fever reducers (such as acetaminophen or Tylenol, and ibuprofen or Advil), can help relieve fever and muscle aches. If you are at high risk for complications (see Risk Factors), then your doctor may prescribe antiviral medications (drugs that fight the virus). They must be started within 2 days to be effective. Certain herbs, supplements, and homeopathic remedies may help some of your symptoms.

Lifestyle

• Drink lots of fluids.
• Rest to restore your energy and avoid complications like pneumonia.
• Eat a diet rich in fresh fruits and vegetables. These foods provide lots of antioxidants (substances that may help boost your immune system), especially vitamins A and C.
• Exercising regularly may cut your risk of flu and help your body respond better to a flu shot.
• Minimize stress and your reaction to stress. Consider yoga, tai chi, or other forms of relaxation on an ongoing basis. Stress can put you at increased risk for viruses like influenza.

Medications

• Pain and fever reducers — include ibuprofen (Advil, Motrin) and acetaminophen (Tylenol) for fever reduction and relief of minor aches and pain. Children under 18 should not take aspirin due to the risk of a rare but serious illness called Reye's syndrome.
• Decongestants — help open your nasal passages so you can breathe easier. If decongestant nasal sprays or drops are used for more than 3 days, however, they can cause rebound congestion. Decongestants are often combined in cold and flu medicines with antihistamines, cough suppressants, and pain relievers. People with heart disease, high blood pressure, diabetes, or glaucoma should not take decongestants. Popular brands of decongestants include Sudafed, Afrin, and Neo-Synephrine.

• Cough medicines — cough suppressants (for a dry cough) or expectorants (for a wet, productive cough that brings up mucous) are available over the counter and by prescription.

• Antiviral medications — Several antiviral medications have been approved by the Food and Drug Administration (FDA) to treat flu, although a number of flu viruses have developed resistance to some of the medications. In addition, using these medications may help contribute to other strains of flu becoming resistant. These drugs must be started within 48 hours of becoming sick to be effective. Medications include:

  • Oseltamivir (Tamiflu): The FDA requires Tamiflu to carry a warning that people who have the flu, especially children, may be at increased risk of confusion and injuring themselves after taking Tamiflu.
  • Zanamavir (Relenza)
  • Amantadine (Symmetrel): Recently, most flu viruses in the U.S. have been resistant to Symmetrel
  • Rimantadine (Flumadine): Recently, most flu viruses in the U.S. have been resistant to Flumadine

Nutrition and Dietary Supplements

Because supplements may have side effects or interact with medications, you should take them only under the supervision of a knowledgeable health care provider. Be sure to talk to your doctor about any supplements you are taking or considering taking.

• Warm liquids — Chicken soup and warm liquids (broth, tea) can help soothe a sore throat and loosen mucus, which in turn helps ease congestion from the flu.
• Probiotics (Lactobacillus) — So-called “good” bacteria or probiotics help prevent infections in the intestines, and there is preliminary evidence that they might help prevent colds, too, although they have not been studied for the flu. One study found that children in daycare centers who drank milk fortified with Lactobacillus had fewer and less severe colds. Several studies that examined probiotics combined with vitamins and minerals also found a reduction in the number of colds caught by adults, although it’s not possible to say whether the vitamins, minerals, or probiotics were most responsible for the benefit.
• Zinc — Your body needs zinc for its immune system to function properly, so it has long been thought that zinc could help protect against catching a cold or flu. But the evidence has been decidedly mixed, with some studies finding a benefit from zinc lozenges and others showing no effect. Recently, a review of studies that compared zinc to placebo found that most of them had flaws that made any positive results unreliable. Only 4 studies were deemed reliable, and 3 found no benefit from zinc lozenges. The remaining positive study suggested that zinc nasal sprays might help reduce nasal stuffiness. If you do decide to try zinc lozenges for a cold, remember that getting too much zinc (more than 50 mg per day over a long period of time) can be dangerous.
• Spirulina — In test tubes, spirulina seems to be able to stop some flu viruses from reproducing. It isn't known whether it will have the same effect in humans, however.

Herbs

The use of herbs is a time honored approach to strengthening the body and treating disease. Herbs, however, can trigger side effects and can interact with other herbs, supplements, or medications. For these reasons, you should take herbs care, under the supervision of a health care practitioner. Before giving any herbs to a child to treat the flu, talk to your pediatrician.

• Andrographis (Andrographic paniculata) — One study found that andrographis, an herb used in Ayurvedic medicine, combined with eleuthero or Siberian ginseng (Eleutherococcus senticosus) in a formula called Kan Jang, helped reduce symptoms and shorten the duration of the flu. More studies are needed to say for sure whether it is effective.
• Echinacea (Echinacea purpurea, 300 mg 3 times per day) — Although evidence on whether echinacea works to prevent or treat colds and flu has gone back and forth, recent evidence is encouraging. An analysis of 14 scientific studies found that people who took Echinacea reduced their risk of getting a cold by 58% and reduced the duration of a cold by an average of a day and a half. However, many of the studies used Echinacea in combination with another herb or vitamin, so it’s impossible to say which one was responsible for the benefit. The analysis looked at colds, not flu, so the evidence may be more mixed as to whether Echinacea can help prevent flu. Echinacea should not be used by women who are pregnant or breastfeeding, or by anyone taking drugs that suppress the immune system (such as corticosteroids or methotrexate).
• Garlic (Allium sativum) — Some studies suggest taking garlic may help reduce your risk of getting an upper respiratory infection, such as a cold or flu. More studies are needed to tell whether garlic has any true benefit for flu, however. Because garlic can increase the risk of bleeding, people who take anticoagulants (blood thinners, such as aspirin or warfarin) should not take garlic. Women who are pregnant or breastfeeding should talk to their doctor before taking garlic supplements.
• Elder or elderberry (Sambucus nigra) — By lessening congestion and possibly increasing perspiration, elder may help reduce the symptoms of colds and flu. One study suggested that using a standardized elderberry extract, Sambucol™, could shorten the duration of flu by about 3 days. Sambucol™ also contains other herbs plus vitamin C, so it isn’t known whether elder by itself would have the same effect. Pregnant and breastfeeding women should not take elder.
• Eucalyptus (Eucalyptus globulus) — Eucalyptus is used in many remedies to treat cold and flu symptoms, particularly cough. It can be found in many lozenges, cough syrups, and vapor baths throughout the United States and Europe. Fresh leaves can be used in teas and gargles to soothe sore throats. Ointments containing eucalyptus leaves are also applied to the nose and chest to relieve congestion and loosen phlegm.
• Goldenseal (Hydrastis canadensis) — Goldenseal is often combined with echinacea in herbal cold and flu remedies, although scientific evidence that it works is lacking. Women who are pregnant or breastfeeding should talk to their doctor before taking goldenseal.
• Licorice (Glycyrrhiza glabra) — Licorice root is a traditional treatment for sore throat, although scientific evidence is lacking. Licorice interacts with a number of medications, so ask your doctor before taking it. People with high blood pressure or heart disease, women who are pregnant or breastfeeding, and those who take anticoagulants (blood thinners) should not take licorice.
• Marshmallow (Althea officinalis) — Although there isn’t any scientific evidence that it works, marshmallow has been used traditionally to treat sore throat and cough.
• Peppermint (Mentha x piperita) — Like eucalyptus, peppermint is widely used to treat cold and flu symptoms. Its main active agent, menthol, is a good decongestant. Menthol also thins mucus and works as an expectorant, meaning that it helps loosen and break up phlegm. It is soothing and calming for sore throats and dry coughs as well.
• Slippery elm (Ulmus fulva) — Slippery elm may help ease a sore throat and has been used traditionally for this purpose, although scientific evidence is lacking.

Homeopathy

Although very few studies have examined the effectiveness of specific homeopathic therapies, professional homeopaths may consider the following remedies for the treatment of the flu based on their knowledge and experience. Before prescribing a remedy, homeopaths take into account a person's constitutional type. A constitutional type is defined as a person's physical, emotional, and psychological makeup. An experienced homeopath assesses all of these factors when determining the most appropriate treatment for each individual.

• A combination remedy including Aconite, Gelsemium, Eucalyptus, Ipecacuanha, Phosphorus, Bryonia, and Eupatorium perfoliatum
• A mixture of Anas barbarice hepatis and Cordis extractum
• Gelsemium — for chills, weakness, lack of energy, fever, and headaches in the back and top of the head; this is one of the most common homeopathic remedies for the flu
• Eupatorium perfoliatum — for deep aches, sneezing, and coughing
• Nux vomica — for violent vomiting, irritability, dry cough, chills, and a stuffy nose that develops into a watery, irritating discharge

Warnings and Precautions

If you are in any of the high risk groups described in the Risk Factors section, be sure to call your doctor at the earliest signs of flu symptoms. The sooner you are treated, the less likely you are to develop complications.

Prognosis and Complications

Most healthy people get over the flu in within 2 weeks. For those at high risk, certain serious, even life threatening, complications can occur, including:

• Pneumonia (most common in children)
• Encephalitis (an infection of the brain)
• Secondary bacterial infection elsewhere in the body

Alvarez-Olmos MI. Probiotic agents and infectious diseases: a modern perspective on a traditional therapy. Clin Infect Dis. 2001;32(11):1567-1576.

Barak V, Birkenfeld S, Halperin T, Kalickman I. The effect of herbal remedies on the production of human inflammatory and anti-inflammatory cytokines. Isr Med Assoc J. 2002;4(11 Suppl):919-922.

Barak V, Halperin T, Kalickman I. The effect of Sambucol, a black elderberry-based, natural product, on the production of human cytokines: I. Inflammatory cytokines. Eur Cytokine Netw. 2001;12(2):290-296.

Barrett BP, Brown RL, Locken K, Maberry R, Bobula JA, D'Alessio D. Treatment of the common cold with unrefined Echinacea: a randomized, double-blind, placebo-controlled trial. Ann Intern Med. 2002;137:936-946.

Belongia EA, Berg R, Liu K. A randomized trial of zinc nasal spray for the treatment of upper respiratory illness in adults. Am J Med. 2001;111(2):103-108.

Blumenthal M, Goldberg A, Brinckmann J. Herbal Medicine: Expanded Commission E Monographs. Newton, MA: Integrative Medicine Communications; 2000:57-61, 233-239, 240-243, 244-248, 297-303.

Brankston G, Gitterman L, Zahir H, Lemieux C, Gardam M. Transmission of influenza A in human beings. The Lancet Infectious Diseases. 2007; 7(4):

Brinkeborn RM, Shah DV, Degenring FH. Echinaforce and other Echinacea fresh plant preparations in the treatment of the common cold. A randomized, placebo controlled, double-blind clinical trial. Phytomedicine. 1999;6(1):1-6.

Cohen S, Hamrick N, Rodriquez MS, Feldman PJ, Rabin BS, Manuck SB. Reactivity and vulnerability to stress-associated risk for upper respiratory illness. Psychosom Med. 2002;64(2):302-310.

Cummings S, Ullman D. Everybody's Guide to Homeopathic Medicines. 3rd ed. New York, NY: Penguin Putnam; 1997: 57, 69.

de Vrese M, Winkler P, Rautenberg P, Harder T, Noah C, Laue C, et al. Probiotic bacteria reduced duration and severity but not the incidence of common cold episodes in a double blind, randomized, controlled trial. Vaccine. 2006 Nov 10;24(44-46):6670-4.

Douglas RM, Chalker EB, Treacy B. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2000;(2):CD000980.

Eby GA. Zinc ion availability—the determinant of efficacy in zinc lozenge treatment of common colds. J Antimicrob Chemother. 1997;40:483-493.

Ferri: Ferri's Clinical Advisor 2009, 1st ed. Philadelphia, PA: Mosby Elsevier. 2009.

Fiore C, Eisenhut M, Krausse R, Ragazzi E, Pellati D, Armanini D, Bielenberg J. Antiviral effects of Glycyrrhiza species. Phytother Res. 2007 Sep 20; [Epub ahead of print]

Fortes C, Forastiere F, Agabiti N, et al. The effect of zinc and vitamin A supplementation on immune response in an older population. J Am Geriatr Soc. 1998;46:19–26.

Glatthaar-Saalmuller B, Sacher F, Esperester A. Antiviral activity of an extract derived from roots of Eleutherococcus senticosus. Antiviral Res. 2001;50(3):223-8.

Gruenwald J, Brendler T, Jaenicke C, et al, eds. PDR for Herbal Medicines. 2nd ed. Montvale, NJ: Medical Economics Company Inc; 2000:283-287, 477-479.

Guo R, Pittler MH, Ernst E. Complementary medicine for treating or preventing influenza or influenza-like illness. Am J Med. 2007 Nov;120(11):923-929.e3. Review.

Guralnik M, Rosenbloom RA, Petteruti MP, Lefante C. Limitations of current prophylaxis against influenza virus infection. Am J Ther. 2007 Sep-Oct;14(5):449-54. Review.

Hatakka K, Savilahti, Ponka A, et al. Effect of long term consumption of probiotic milk on infections in children attending day care centers: double-blind, randomized trial. BMJ. 2001;322(7298):1327.

Hayashi K, Hayashi T, Kojima I. A natural sulfated polysaccharide, calcium spirulan, isolated from Spirulina platensis: in vitro and ex vivo evaluation of anti-herpes simplex virus and anti-human immunodeficiency virus activities. AIDS Res Hum Retroviruses. 1996;12:1463–1471.

Hewson-Bower B, Drummond PD. Psychological treatment for recurrent symptoms of colds and flu in children. J Psychosom Res. 2001;51(1):369-377.

Hirt M, Nobel Sion, Barron E. Zinc nasal gel for the treatment of common cold symptoms: A double-blind, placebo-controlled trial. ENT J. 2000;79(10):778-780, 782

Jaber R. Respiratory and allergic diseases: from upper respiratory tract infections to asthma. Prim Care. 2002;29(2):231-261.

Jackson JL, Lesho E, Peterson C. Zinc and the common cold: a meta-analysis revisited. J Nutr. 2000;130(5S Suppl):1512S-1515S.

Jonas WB, Jacobs J. Healing with Homeopathy: The Doctors' Guide. New York, NY: Warner Books; 1996: 213.

Kligler B. Echinacea. Am Fam Physician. 2003;67(1):77-80.

Kohut ML, Cooper MM, Nickolaus MS, Russell DR, Cunnick JE. Exercise and psychosocial factors modulate immunity to influenza vaccine in elderly individuals. J Gerontol A Biol Sci Med Sci. 2002;57(9):M557-M562.

Kruzel T. The Homeopathic Emergency Guide. Berkeley, Calif: North Atlantic Books; 1992:190-196.

Lindenmuth GF, Lindenmuth EB. The efficacy of echinacea compound herbal tea preparation on the severity and duration of upper respiratory and flu symptoms: a randomized, double-blind placebo-controlled study. J Altern Complement Med. 2000;6(4):327-334.

Mahady GB. Echinacea: recommendations for its use in prophylaxis and treatment of upper respiratory tract infections. Nutr Clin Care. 2001;4(4):199-208.

Mandell G, Bennett J, Dolin R. Mandell, Bennett, & Dolin: Principles and Practice of Infectious Diseases, 6th ed. Philadelphia, PA: Elsevier, Inc. 2005.

McElroy BH, Miller SP. Effectiveness of zinc gluconate glycine lozenges against the common cold in school-aged subjects: a retrospective chart review. Am J Ther. 2002;9(6):472-475.

Melchart D, Linde K, Fischer P, Kaesmayr J. Echinacea for preventing and treating the common cold. [Review]. Cochrane Database Syst Rev. 2000;(2):CD000530.

Melchart D, Walther E, Linde K, Brandmeier R, Lersch, C. Echinacea root extracts for the prevention of upper respiratory tract infections: a double-blind, placebo-controlled randomized trial. Arch Fam Med. 1998;7:541-545.

Prasad AS, Fitzgerald JT, Bao B, Beck FW, Chandrasekar PH. Duration of symptoms and plasma cytokine levels in patients with the common cold treated with zinc acetate. A randomized, double-blind, placebo-controlled trial. Ann Intern Med. 2000;133(4):245-252.

Reid MR, Mackinnon LT, Drummond PD. The effects of stress management on symptoms of upper respiratory tract infection, secretory immunoglobulin A, and mood in young adults. J Psycosom Res. 2001;51(6):721-728.

Rotblatt M, Ziment I. Evidence-Based Herbal Medicine. Philadelphia, PA: Hanley & Belfus, Inc; 2002:166-169, 221-225, 252-258, 369-371.

Rothberg M, Haessler S, Brown R. Complications of Viral Influenza. The American Journal of Medicine. 2008; 121(4).

Roettger B. Homeopathy as an effective treatment for colds and flus. Nutr Sci News Mag. August 1995.

Roxas M, Jurenka J. Colds and influenza: a review of diagnosis and conventional, botanical, and nutritional considerations. Altern Med Rev. 2007 Mar;12(1):25-48. Review.

Scaglione F, Cattaneo G, Alessandria M, Cogo R. Efficacy and safety of the standardized ginseng extract G115 for potentiating vaccination against common cold and/or influenza syndrome. Drugs Exp Clin Res. 1996;22:65-72.

Schulz V, Hansel R, Tyler V. Rational Phytotherapy: A Physicians' Guide to Herbal Medicine. 3rd ed. Berlin, Germany: Springer; 1998:150.

Shah SA, Sander S, White CM, Rinaldi M, Coleman CI. Evaluation of echinacea for the prevention and treatment of the common cold: a meta-analysis. Lancet Infect Dis. 2007 Jul;7(7):473-80. Review. Erratum in: Lancet Infect Dis. 2007 Sep;7(9):580.

Takkouche B, Regueira-Mendez C, Garcia-Closas R, Figueiras A, Gestal-Otero JJ. Intake of vitamin C and zinc and risk of common cold: a cohort study. Epidemiology. 2002;13(1):38-44.

Turner RB. Ineffectiveness of intranasal zinc gluconate for prevention of experimental rhinovirus colds. Clin Infect Dis. 2001;33(11):1865-1870.

Turner RB, Riker DK, Gangemi JD. Ineffectiveness of Echinacea for prevention of experimental rhinovirus colds. Antimicrob Agents Chemother. 2000;44:1708-1709.

Ullman D. Homeopathic Medicine for Children and Infants. New York, NY: Penguin Putnam; 1992: 107.

Ullman D. The Consumer's Guide to Homeopathy. New York, NY: Penguin Putnam; 1995: 229.

Van Straten M, Josling P. Preventing the common cold with a vitamin C supplement: a double-blind, placebo-controlled survey. Adv Ther. 2002;19(3):151-159.

Zakay-Rones Z, Varsano N, Zlotnik M, et al. Inhibition of several strains of influenza virus in vitro and reduction of symptoms by an elderberry extract (Sambucus nigra L.) during an outbreak of influenza B Panama. J Altern Complement Med. 1995;1(4):361-369.