A Beginner’s Guide to Cold & Flu Supplements

Last year, WebMD reported that Americans spent more than $1.5 billion on cold and flu supplements—and that the growth of this market segment is outpacing traditional over-the-counter drugs by more than two-fold.

If you’re thinking about joining the ranks and handing over your money for a cold and flue supplement this season, we’ll take a science-backed look at what works and what doesn’t, potential risks and side effects, and what factors to keep in mind when buying.

Let’s dive right in.

Are Cold & Flu Supplements ‘Effective’?

Looking at the situation from a high-level perspective, the National Center for Complementary and Integrative Health (NCCIH) reports: “There is currently no strong scientific evidence that any natural product is useful against the flu.”

So, if you’re looking to maximize your defenses, they emphasize, “vaccination is the best protection.”

Robert T. Schooley, head of the infectious-diseases division at the University of California at San Diego, mirrors this sentiment when stating, “Nothing except a flu shot prevents the flu, and no dietary supplements can prevent or treat it.” He also adds “there is scant evidence that supplements can prevent or treat colds.’’

But during our years of research, we’ve learned that the topic of dietary supplements is incredibly nuanced. This is due in no small part to the fact that, except for a handful of specifications regarding the claims manufacturers are allowed make, these products are almost wholly unregulated by the Food and Drug Administration (FDA).

Even the term itself can reference anything from a vitamin, a mineral, and an herb, to a botanical, amino acid, or concentrate—or any combination thereof.

And as we’ll discuss in a moment, this nuance and ambiguity also extend to the quality of clinical studies supporting the effectiveness of supplements, whether for addressing colds, the flu, or other conditions.

For example, some might not be peer-reviewed or double-blind; some might have too small a sample size; some could have inherent design flaws that influence their findings; some might be funded directly by supplement manufacturers—the list could go on. 

Weaving these factors together, rarely is an ingredient classified simply as ‘effective’ or ‘ineffective’ by sites like the Natural Medicines Database, WebMD, and Examine.com. Instead, it’s often a gradation based on thousands of variables.

So, while natural ingredients—whether on their own or in combination—might not directly affect the viruses that cause colds and flu like vaccines, there is some clinical evidence they might be able to help address some of the symptoms caused by these illnesses.

With this important caveat in mind, let’s zoom in and take a look at some of the most commonly used supplement ingredients for fighting cold and flu symptoms, as well as their overall level of clinical support. 

Evaluating Common Ingredients Found in Cold & Flu Supplements

Here, we’ve provided a quick-reference chart looking at high-level clinical support for popular supplement ingredients. Further down, you’ll find a more in-depth discussion of the nuances.

Common Cold & Flu Supplement Ingredients Overall Clinical Support
Buckwheat Honey A couple of studies. May reduce cough frequency and improve sleep quality for children with the common cold.
Elderberry A small number of low-quality studies show it may reduce cold and flu symptoms.
Echinacea Several professional reviews of the available clinical evidence report statistically insignificant benefits.
Garlic Insufficient evidence, although chewing garlic can work as a natural expectorant and decongestant.
Geranium Extract Some trials show it may address bronchitis and acute sinusitis symptoms, but evidence quality is low or very low.
Ginseng Eight studies indicate taking 100-200mg daily for 3-4 months may reduce the likelihood of getting a respiratory tract infection from cold or flu, or from getting a second infection in the same season.
Glutamine What little evidence there is indicates it may work best for those who compete in long-distance ultras.
Homeopathic Remedies No good quality evidence for their effectiveness in treating any health condition.
Fish Oil (Omega-3) Limited evidence regarding efficacy for cold and flu symptoms.
Pelargonium sidoides Preliminary evidence indicates it may improve symptoms of acute bronchitis, as well as reduce cold severity and duration.
Probiotics Insufficient research related to cold and flu symptoms.
Pycnogenol One study showing it may decrease symptoms of cold and shorten its course.
Turmeric No clinical support for addressing cold and flu symptoms.
Vitamin C Limited evidence; some positive and some neutral. If it works at all, it’s considered a proactive approach and doesn’t work once you’ve fallen ill.
Vitamin D Plays an important role in immune function, but limited clinical evidence that it can address cold and flu symptoms in otherwise healthy individuals.
Willow Bark Contains salicin, which may relieve aches and pains about as well as OTC aspirin.
Zinc If started within 24 hours of symptoms and taken continuously for two weeks, oral zinc lozenges may reduce the duration of common cold. Routine supplementation is not recommended.

Buckwheat Honey

According to the NCCIH, a couple of small children’s studies have looked at the impact of buckwheat honey on common cold symptoms, finding that it’s “superior to placebo for reducing the frequency of cough, reducing cough, and improving quality of sleep for children with the common cold."


The University of Maryland Medical Center indicates that elderberry is one of many fruits and vegetables that contain high levels of antioxidants, which have been shown to play a role in fighting free radical damage and maintaining good overall health.

And in some clinical trials, Examine.com reports that it’s been shown to potentially reduce cold and flu symptoms. But due to the small number of studies, in addition to the low methodological quality used in some of them, they report, “both the efficacy and safety of elderberry are still in doubt.”


The NCCIH tells us that several reviews (including one from Cochrane) of randomized controlled trials indicate that Echinacea’s “overall evidence for clinically relevant treatment effects is weak” when it comes to cold and flu symptoms. 

Examine.com adds that daily Echinacea “might reduce the risk and duration of upper respiratory infections” caused by cold and flu, although “examining the trials reveals a positive but statistically insignificant trend.” 


The NCCIH states that because “only a few clinical trials have been conducted examining the effects of garlic supplements on the common cold,” a “recent Cochrane review concluded that there is insufficient clinical trial evidence” for its ability to prevent or treat it.

Addressing specific claims, SuperFoodly writes there’s insufficient data that garlic can act as an antiviral, although chewing it might act as a natural expectorant and decongestant.

Geranium Extract

There is some evidence that geranium extract “may be helpful in relieving symptoms of acute bronchitis, acute sinusitis, and the common cold in children and adults,” the NCCIH reports.

However, a 2013 Cochrane review of 10 randomized clinical trials (only eight of which were of sufficient quality for inclusion) found “the quality of the evidence low or very low for all major outcomes, as there were few studies per disease entity, and all were from the same investigator (the manufacturer) and performed in the same region (Ukraine and Russia).”


Writing for Rodale Wellness, Mark Moyad, MD, MPH, often recommends that his patients take 100-200 mg of ginseng per day “for prevention during cold and flu season,” since “it’s been studied against a placebo in at least five different clinical trials. In them, it reduced the number of colds by 25 percent (not that impressive, but not that bad) and the duration of colds or acute respiratory infections by as much as six days (very impressive).”

With this said, WebMD lists American ginseng as possibly effective for addressing cold and flu-related respiratory tract infections but explains that achieving this effect might require taking it twice daily for three to four months.

They also note that some evidence indicates ginseng may reduce the chances of getting repeat colds in the same season, but it may not do so for the first cold of the season. 

Finally, they report that taking Panax (Asian) ginseng might reduce the chances of contracting a cold or the flu, but it doesn’t appear to reduce flu symptoms or illness length.


Examine.com reports that glutamine’s ability to support immune function during illness is well known, although “its effects on the common cold are not well understood.” Neither WebMD nor the Natural Medicines Database indicated its effectiveness for cold or flu, though.

Based on the preliminary evidence, Examine.com notes, “supplementation is more likely to benefit people who participate in prolonged cardiovascular exercise, such as ultra-marathons.”

Homeopathic Remedies

The HighYa team has written extensively on the topic of homeopathy, from its basics to common theories about how it works.

During this time, we’ve learned that as recently as 2015, Australia’s National Health and Medical Research Council performed a systematic review of more than 1,800 studies and found there’s “no good quality evidence to support the claim that homeopathy is effective in treating health conditions”—including cold and flu symptoms.

Fish Oil (Omega-3)

We’ve learned in the past that omega-3 supplementation can provide a variety of benefits; from reducing triglycerides, cholesterol, and the risk of heart disease, to addressing rheumatoid arthritis and high blood pressure.

And although the flu and common cold are caused by viral infection, Prevention reports “Omega 3s increase the activity of phagocytes—cells that fight flu by eating up bacteria—according to a study by Britain's Institute of Human Nutrition and School of Medicine. Other research shows that omega-3s increase airflow and protect lungs from colds and respiratory infections.”

» RELATED: Best Omega-3 Supplements Buying Guide

Pelargonium Sidoides

Mark Moyad, MD, writes that there are two randomized trials indicating that taking 1.5 ml of this species of South African geranium three times per day for ten days can improve symptoms of acute bronchitis, which he says is usually caused by a virus.

Specifically, it seems to work “better for nasal congestion and drainage, sneezing, sore and scratchy throat, hoarseness, and headache than for fever, cough, and muscle aches.”

With these nuances in mind, Examine.com summarizes it “seems to reduce the duration and severity of colds, but the evidence is still preliminary.”


Like omega-3s, we’ve learned there’s ever-mounting clinical support for the ability for probiotic supplements to provide a variety of benefits, including improved digestion, reduced bloating and gassiness, and relieving symptoms of diarrhea and irritable bowel disease (to name just a few).

Although the NCCIH indicates several controlled trials have been conducted on various strains at different dosages, there’s “currently not enough research … to determine whether probiotics may prevent colds.”

However, Examine.com points out that “probiotics might help prevent infections of the upper respiratory tract, but the evidence is still too weak to recommend their use.”


Searching the National Institutes of Health’s PubMed, we encountered one Italian study from 2014 indicating that pycnogenol (a trademarked product derived from pine bark that may improve blood flow) could also help “decrease symptoms of cold and shorten its course, also preventing some complications.”


You’ll often find turmeric promoted as a traditional approach to fighting cold and flu symptoms, although across sites like WebMD, the Natural Medicines Database, Examine.com, and NIH’s PubMed, we didn’t encounter any clinical evidence supporting its efficacy.

Vitamin C

Based on a 2013 Cochrane review, 29 trials involving 11,306 participants found the “regular ingestion of vitamin C had no effect on common cold incidence in the ordinary population.”

However, they balance this by noting that “based on 31 study comparisons with 9745 common cold episodes,” regular supplementation “had a modest but consistent effect in reducing the duration of common cold symptoms.”

The NCCIH summarizes this as, “for most people, vitamin C does not prevent colds and only slightly reduces their length and severity.”

Here’s Examine.com’s take: Based on the available evidence, “Vitamin C can reduce the duration of colds (and even help ward them off, if you're an athlete), but only if you've regularly been supplementing. If you start when you're sick, it's too late."

Vitamin D

There’s evidence indicating a strong link between vitamin D deficiency and reduced immune function, although Mark Moyad, MD, emphasizes that “If you have normal or near-normal levels, vitamin D won't help you fight off viruses.”

With this in mind, Examine.com reports “Large systematic reviews have found that supplementation can help prevent upper respiratory infections.”

Willow Bark

According to WebMD, willow bark contains a chemical called salicin, which sometimes works as well as over-the-counter pain reliever aspirin. As such, it might help address aches and pains commonly experienced by cold and flu sufferers.

However, there’s no reported clinical evidence for any directly related cold and flu symptom benefits.


The NCCIH tells us that zinc’s effects on the common cold have been studied in “several randomized controlled trials, systematic reviews, and meta-analyses,” finding that oral lozenges “may reduce the duration of the common cold, when started within 24 hours and taken for a time period of less than 2 weeks.”

Examine.com reemphasizes the importance of taking these lozenges “throughout the day, starting from the very first symptoms of a cold” to reduce the illness’s duration. However, they point out that you “should not exceed 100 mg of zinc per day for a week,” and WebMD indicates that “routine zinc supplementation is not recommended without the advice of a healthcare professional.”

Are there any other potential concerns, side effects, or interactions caused by common ingredients found in cold and flu supplements?  

Potential Side Effects Related to Cold & Flu Supplement Ingredients

Writing for WebMD, R. Morgan Griffin states: “Experts agree that popular natural cold and flu remedies seem to be safe for the average person. That's important when dealing with unproven treatments. As long as there's little risk in trying a supplement, the evidence of a benefit doesn't need to be quite so strong.”

Even the NCCIH points out that, if these ingredients cause any side effects at all, they likely won’t be worse than mild, temporary nausea and other gastrointestinal symptoms.

» RELATED: Can Dietary Supplements and Vitamins Cause Dangerous Side Effects?

With this said, many of these same sites indicate that the likelihood of side effects from vitamin C increases when taken in high doses (more than 2,000 mg per day).

And despite the clinical evidence indicating certain probiotic strains can provide a variety of digestive benefits, we’re told that little is known about their long-term safety.

The NCCIH warns that “honey should not be used in children younger than one year of age because of the risk of botulism,” while Examine.com tells us that Echinacea can interact with some immunosuppressive medications.

What to Look for When Buying a Cold & Flu Supplement

While there are always nuances when it comes to examining clinical evidence related to ingredients, buying a dietary supplement is much more straightforward. This is because the same general guidelines apply, regardless of the manufacturer’s advertising claims.

For example, you’ll want to focus on companies who:

  • Offer competitive pricing (there’s no indication that paying more for any of these ingredients will improve the impact on cold and flu symptoms).
  • Provide a complete list of ingredients, including dosages, with no proprietary blends.
  • Support their claims with peer-reviewed, double-blind, placebo-controlled clinical studies.
  • Offer robust refund policies (at least 30 days), with realistic S&H charges and no restocking fees.
  • Feature mostly positive online customer feedback. Remember, if you frequently encounter the same complaint(s), this could be an indication you’ll experience much of the same.

Taking everything we’ve discussed here, what’s the bottom line about buying a cold or flu supplement? 

The Bottom Line

Whether or not you should purchase a cold and flu supplement largely comes down to your expectations.

In other words, if you’re expecting any of these ingredients to provide fool-proof protection from falling ill this season, there doesn’t seem to be enough reported clinical evidence to support this.

However, if you’re looking for a little extra boost this season, sites like the Natural Medicines Database, Examine.com, and WebMD, as well as organizations like Cochrane and the National Center for Complementary and Integrative Health, indicate that ingredients like buckwheat honey, garlic, ginseng, Pelargonium sidoides, vitamins C and D, and zinc may provide some relief from cold and flu symptoms.

As always, though, be sure to discuss the situation with your healthcare provider before handing over any of your hard-earned money, who can help you make a more informed decision—and avoid potential side effects and interactions—based on your diagnosis.

In the meantime, Examine.com recommends that outside of purchasing a supplement, other options for keeping yourself healthy during cold and flu season include eating a nutrient-rich diet, getting plenty of sleep, managing stress, avoiding others who are sick, and always making sure to wash your hands before touching your face.

» READ NEXT: Before Buying a Dietary Supplement, Follow These Steps to Understand Its Claims

Derek Lakin

With more than a decade of experience as a copywriter, Derek takes a detail-oriented, step-by-step approach to help you shop smarter. Whether it’s nutritional supplements or new scams, he believes an informed consumer is a happy customer.