It’s that time of year when quacks and grifters push flu and cold supplements that have little or no scientific support for their effectiveness. In other words, they are generally a waste of money, as they do nothing to prevent or reduce the course of the flu or cold.

The 2025-26 flu season has been particularly severe due to the emergence of the new subvariant, A(H3N2) virus subclade J.2.4.1, also known as the “H3N2 subclade K.” The best way to prevent the flu or, at a minimum, reduce the risk of hospitalization is with the flu vaccine.

This article will review some of the more popular supplements that are claimed to prevent or treat the flu or cold. Spoiler alert — don’t get your hopes up for a simple cure.

The myth of flu and cold supplements

One of the most fundamental misconceptions about cold and flu quack treatments is the “boosting the immune system” myth. The supplement pushers tend to oversimplify the immune system – they do this because the immune system is so complicated, they need to simplify it so that they can sell their worthless products.

Moreover, they try to make it seem your immune system is pathetic, weak, and useless without their expensive, miracle, magical pills.

In fact, the immune system is a huge, complex, interrelated structure that contains an almost infinite variety of biomolecules (especially antibodies), cells, tissues, and organs, generally working in efficient harmony.

Moreover, the immune system is quite resilient. If the immune system were such a weakling, we would all be dead from pathogens before we made it to our 5th year of life. And there is a reason why we make it past your 5th year of life, but I’ll get to that.

If these quacks were actually correct, humans would have died out a few hundred thousand years ago, and birds would be ruling the planet. Birds are cool (and are the only living dinosaurs), but they probably wouldn’t have invented Facebook. 

So, if someone says, “This thing is critical to boosting immunity so that you will never get the flu, cold, or COVID-19,” your first question must be, “Which of the millions of different parts of our immune system is boosted?” They rarely can answer that question.

Your second question should probably be, “Do you have peer-reviewed extraordinary evidence that supports that extraordinary claim?”

Usually, these supplement pushers never have any extraordinary or even ordinary evidence to support their claims.

Back to real science. In general, the immune system is an on/off type of network. It’s either working perfectly well, or it isn’t, and we know the precise conditions that might cause the immune system to start working less perfectly.

According to the Harvard Medical School, the University of Rochester Medical Center, and Science-Based Medicine, we can conclude that:

1. Some chronic conditions, such as stress and malnutrition (a large and long-term calorie and micronutrient deficit), can affect the performance of your immune system.
2. There are a few chronic diseases that can have an impact on the quality of the immune response, diabetes being one of the more prevalent, but there are many others.
3. Some people are born with impaired immune systems. Some may acquire an immune deficiency as a result of certain diseases (HIV/AIDS is the best known). Some medical treatments, like chemotherapy or immunosuppressive therapies, can weaken the immune system. One of the tropes of the immune system pseudoscience is that an infection weakens the immune system; in fact, the sick feeling you have from a cold or other disease can be a part of the immune response.
4. Short-term acute conditions, such as lack of rest and exercise or a poor diet, can temporarily depress the immune system, but that is usually easily reversed. 

Almost everyone, short of those with the health conditions mentioned above, has a well-functioning and highly effective immune system – there is no way to make it better. There is little evidence that a normally functioning immune system can be “boosted.” And by evidence, I mean high-quality randomized clinical or epidemiological studies published in high-quality peer-reviewed journals.

On the other hand, if you really could boost your immune system, is that even a good idea? How can you even fine-tune a “boost” without figuring out the exact amount necessary to get the desired effect?

In fact, there are reasons why we shouldn’t have a “boosted” immune system. For example, overactive immune systems are responsible for allergic conditions such as asthma and eczema. And there’s a type of runaway immune response known as a “cytokine storm” which may be responsible for the high mortality in severe flu pandemics.

Inflammation is normally a healthy response to injury or pathogen invasion, but in some autoimmune diseases, such as rheumatoid arthritis, it can be painful and debilitating.

Additionally, an overactive immune system can become misdirected and start attacking the cells of the host body. This immune system error can cause autoimmune diseases such as arthritis and Type 1 diabetes.

So, no, it really is not a good idea to boost your immune system, even if you could (and you can’t). After you ask one of the flu treatment “boosting immunity” quacks whether they actually have any evidence supporting their nonsense, you should ask how they prevent the serious consequences of a boosted immune system. 

Don’t hold your breath – the supplement pushers probably don’t really understand the immune system. 

One more thing – there is a scientifically supported method to boost your immune system. That would be a vaccine. Actually, vaccines don’t “boost” the immune system generally, it induces a very specific immune response to one antigen, like those found on the influenza virus or SARS-CoV-2.

Flu and cold supplements — top 11 myths

Although I don’t want to bore the reader by debunking every flu and cold treatment quackery on the internet, I thought I’d give you the top 11 with the published science that supports debunking. Because that’s why you’re here, to see the evidence.

Fish oil supplements

Although there is some weak evidence that fish oil may have some effect on cardiovascular health, a systematic review (the pinnacle of the hierarchy of scientific research) showed no change in immune system function as a result of fish oil supplements. 

Of course, given how complicated the immune system is, I would reject any claims that fish oil (or any supplement) has on the immune system unless it was in a large, published clinical trial.

Probiotics

Once again, this claim has some evidence supporting it, but not in the way they think. There is some research (another systematic review) that some probiotics may have some effect on the innate immune system of the gut.  

This doesn’t mean that it affects the adaptive immune system, which protects us from airborne pathogens like the flu. Or measles. 

I’m not sold on the whole gut biome claims that seem to be overhyped, but if you have excess money for these supplements, they probably won’t help treat flu or colds, but at least they won’t do much harm.

Oscillococcinum

Oscillococcinum is a homeopathic preparation, derived from Muscovy duck liver and heart (yes, you read that right), that is claimed to treat the flu. Because of the dilution, there are simply no molecules of duck guts in the homeopathic pill.

Based on this ridiculous figurative and literal quackery (get it), one would not be surprised by a Cochrane systematic review that concludes, “There is insufficient good evidence to enable robust conclusions to be made about Oscillococcinum in the prevention or treatment of influenza and influenza-like illness.”

Homeopathy is pseudoscientific quackery, and it is useless as a flu treatment.

Echinacea

Echinacea has received a substantial marketing effort, based on hype and anecdotes, supporting its use as a supplement to treat colds and flu. In fact, echinacea got its reputation based on a misinterpretation of a Native American claim — it’s the wrong plant!

As for scientific evidence, a systematic review has shown us that it has no effect as a treatment for a cold or flu.

Garlic

Unless you want to keep away from mythical vampires, this claim again lacks any supporting scientific evidence. There is no robust epidemiological or clinical evidence that garlic has any effect on preventing or treating the flu. And a systematic review found no evidence that it improved outcomes with another viral disease, the common cold.

Ginger 

Once again, there is no evidence that ginger is effective as a flu treatment.

Elderberry

A new entrant into the area of cold and flu treatment quackery is elderberry. But a review of the research on elderberry treatment finds that there is only weak and limited evidence that it affects the flu.

Let’s not fall for the argument from ignorance and claim it “may” have an effect. The evidence is unconvincing, and other than non-clinical opinion articles published in alternative medicine journals, we just don’t have robust evidence that elderberry is an effective flu treatment. 

Zinc

Zinc is heavily promoted by the company that makes Zicam, which is often used to treat colds, for which there is some limited and very weak evidence in support of its use. There is some evidence that zinc supplementation for individuals who have a deficiency, extremely rare with a modern diet, can help resistance to some strains of flu. However, for those with no zinc deficiency, excess zinc has absolutely no effect.

Furthermore, a recent review has shown that there is no beneficial effect of zinc on COVID-19 outcomes.

Vitamin D

There is an ongoing trope that we are all deficient in vitamin D, which has something to do with the immune system, according to the woomeisters.

In fact, vitamin D may be deficient in some individuals, especially during the winter. However, does that have much to do with our immunity to colds or flu?

Well, a recent meta-review found that “no association was observed between vitamin D and immunogenic response to influenza vaccination.” Another review of the literature concluded that “the survey of the literature data generates some controversies and doubts about the possible role of vitamin D in the prevention of influenza virus.”

In summary, if one is deficient in vitamin D, that is something that should be corrected, easily done with supplements. But is there any evidence that taking large doses will “boost your immune system,” making it an effective treatment for flu? There is some weak evidence, but it’s more about having appropriate levels of vitamin D rather than taking more will have more of an effect.

Vitamin C

Simply, there are no robust epidemiological or clinical trials that have ever established that vitamin C has anything beyond a statistically and clinically insignificant effect on the course or treatment of the flu. Except in cases where an individual is deficient in vitamin C, very rare in today’s world, vitamin C supplementation has no effects on much of anything.

And again, there is no evidence that vitamin C has an effect on the course and outcomes of COVID-19.

Science-based treatments for cold and flu

There are real, science-based treatments for the influenza virus. Anti-viral drugs, especially amantadine, rimantadine, zanamivir (Relenza), and oseltamivir (Tamiflu) are effective in reducing the course and improving outcomes from influenza. They weren’t developed by magic, but by targeting specific properties of the flu virus. This is why an antiviral against one disease may be totally ineffective against another, such as COVID-19.

Just because we do have effective, evidence-based treatments for the flu, it doesn’t mean that they are a better choice than prevention by the flu vaccine. These treatments are expensive, might have significant adverse effects for some, and must be taken almost as soon as symptoms first appear. 

In case you’re wondering, there probably never will be a vaccine for the common cold. Why? Because the cold is caused by a large number of viruses, it would be difficult for one vaccine to target them all.

Nevertheless, the flu and cold supplements industry will continue to take your money by selling you useless treatments that will do nothing for the flu or colds. And to remind everyone, the flu is not some trivial disease; it is deadly.

The 2024-2025 flu season in the USA was classified as a high-severity season, with significant impacts on public health. Here are the key statistics:

• Estimated Deaths: Approximately 27,000 to 130,000 deaths were attributed to influenza during this season.
• Hospitalizations: Approximately 610,000 to 1.3 million hospitalizations, indicating a substantial burden on healthcare systems.
• Symptomatic Illnesses: There were an estimated 47-82 million symptomatic illnesses reported, highlighting the widespread impact of the flu virus

Worldwide, it kills between 290,000 and 650,000 people annually. Ironically, these numbers have dropped significantly because of mitigation efforts for the much more deadly COVID-19.

Summary of flu and cold supplements

After this long review of the evidence surrounding claims about all of the flu and cold supplements, we can come to one conclusion — they don’t work. They are really a waste of money.

If you catch a cold or flu, these supplements will just be a waste of money.

Citations

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