5 Tips: Natural Products for the Flu and Colds: What Does the Science Say?

It’s that time of year again—cold and flu season. Each year, approximately 5 to 20 percent of Americans come down with the flu. Although most recover without incident, flu-related complications typically lead to at least 200,000 hospitalizations and between 12,000 and 60,000 deaths each year. Colds generally do not cause serious complications, but they are among the leading reasons for visiting a doctor and for missing school or work.

Some people try natural products such as herbs or vitamins and minerals to prevent or treat these illnesses. But do they really work? What does the science say?

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.

There is currently no strong scientific evidence that any natural product is useful against the flu.
Zinc taken orally (by mouth) may help to treat colds, but it can cause side effects and interact with medicines. Zinc is available in two forms—oral zinc (e.g., lozenges, tablets, syrup) and intranasal zinc (e.g., swabs and gels). A 2015 analysis of clinical trials found that oral zinc helps to reduce the length of colds when taken within 24 hours after symptoms start. Intranasal zinc has been linked to a severe side effect (irreversible loss of the sense of smell) and should not be used.

A note about safety: Oral zinc can cause nausea and other gastrointestinal symptoms. Long-term use of zinc, especially in high doses, can cause problems such as copper deficiency. Zinc may interact with drugs, including antibiotics and penicillamine (a drug used to treat rheumatoid arthritis).
Vitamin C does not prevent colds and only slightly reduces their length and severity. A 2013 review of scientific literature found that taking vitamin C regularly did not reduce the likelihood of getting a cold but was linked to small improvements in cold symptoms. In studies in which people took vitamin C only after they got a cold, vitamin C did not improve their symptoms.

A note about safety: Vitamin C is generally considered safe; however, high doses can cause digestive disturbances such as diarrhea and nausea.
Echinacea has not been proven to help prevent or treat colds. Echinacea is an herbal supplement that some people use to treat or prevent colds. Echinacea products vary widely, containing different species, parts, and preparations of the echinacea plant. Reviews of research have found limited evidence that some echinacea preparations may be useful for treating colds in adults, while other preparations did not seem to be helpful. In addition, echinacea has not been shown to reduce the number of colds that adults catch. Only a small amount of research on echinacea has been done in children, and the results of that research are inconsistent.

A note about safety: 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 probiotic supplements may help to prevent colds is weak, and little is known about their long-term safety. Probiotics are a type of “good bacteria,” similar to the microorganisms found in the body, and may be beneficial to health. Probiotics are available as dietary supplements and yogurts, as well as other products such as suppositories and creams. Although a 2015 analysis of research 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.

A note about safety: Little is known about the effects of taking probiotics for long periods of time. Most people may be able to 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 side effects. Probiotics should not be used by people with serious underlying health problems except with close monitoring by a health care provider.