It’s that time of year when dozens of common cold treatments are all over the place. On TV advertisements. On displays in your pharmacy. Once again, it’s time to take a look at these lotions and potions to determine which work and which are complete pseudoscientific nonsense.
There are literally a dozen or more homeopathic, herbal, and other unproven concoctions to prevent or treat the common cold, caused by rhinovirus. These common cold treatments are a significant part of the estimated global US$278 billion supplement and nutraceutical industry.
These alternative medicine – so named because there is no scientific evidence supporting their efficacy, let alone safety – products make claims that are so wonderful, many people take them. Then they themselves tell their friends how fast they got rid of their cold. Or that their cold wasn’t as bad after taking the supplement.
Essentially, the whole industry is mostly based on anecdotes, untested claims and the placebo effect. Colds are self-limiting infections, meaning an infection generally lasts some random amount of time, with most people recovering within 7-10 days.
We’re going to review some of the most well-known common cold treatments (there isn’t enough time to review them all), along with what real science says about them in high quality systematic reviews in peer-reviewed, high impact medical journals. This article will review all of the common cold treatments that seem to be out there. Spoiler alert – most don’t work.
One major problem is that the determination of the length and severity of the course of the common cold is entirely subjective. Since the disease is rather mild with few serious complications, it’s hard to determine when it exactly stopped and started, and how bad it was. So, positive results, if they exist, should be treated with a high degree of skepticism.
Echinacea products have not here been shown to provide benefits for treating colds, although, it is possible there is a weak benefit from some Echinacea products: the results of individual prophylaxis trials consistently show positive (if non-significant) trends, although potential effects are of questionable clinical relevance.
The authors make an important point that bears repeating – “questionable clinical relevance.” Evidence (or better yet science) based medicine not only demands high quality research to support a clinical decision, but that the evidence must show some clinical relevance.
If echinacea shows just a 10% lower risk of a cold, and really doesn’t shorten the length of the disease, is it worth the cost and slight adverse effects from the supplement? And the lower risk appears to be, from a statistical point of view, barely significant. At such a low level of benefit, it’s entirely possible that we’re observing a placebo effect, which really has no meaning in medicine. It means it failed.
In another study, in the very high-impact in the New England Journal of Medicine, the researchers concluded:
The results of this study indicate that extracts of E. angustifolia root, either alone or in combination, do not have clinically significant effects on infection with a rhinovirus or on the clinical illness that results from it.
So, once again, we have research published in high quality journals that show that there is no evidence that Echinacea have any important effect on the common cold. Of course, I’ve heard dozens of anecdotal comments along the line of “my wife’s brother’s barber’s cousin” got over the cold after taking it. Well, that’s an anecdote, and, repeat after me, anecdotes don’t equal data.
One more thing – does Echinacea have a plausible biological effect on the immune system, which is a highly complex interaction of cells, organs, proteins, factors, complements and dozens of other components. The immune system has evolved over a billion years to do what it does well – attack and destroy infections. How can Echinacea make the immune system attack rhinovirus any better than it does now? One of the biggest myths of the alternative medicine industry is that it can “boost” the immune system. It can’t.
Amusingly, Echinacea’s modern-day use as a cold remedy dates to the 1960’s when a Swiss herbal supplement maker who, during a trip to South Dakota in the 1960s, was erroneously told echinacea was used for cold prevention by Native American tribes who lived in the area. They did no such thing. In other words, its current use wasn’t even based on a myth or some legend, but on a mistake.
The history of using vitamin C to treat the common cold traces back to Linus Pauling‘s 1970 book, Vitamin C and the Common Cold. That book set off a huge run on vitamin C, which became the go-to supplement for those who wanted to prevent or treat colds. A few years later, Pauling updated the book to claim that it also was good for the flu.
Even back then there was criticism of the science behind it, which continues to today. And now we have real scientific evidence that should make you quite skeptical of Pauling’s claims. As common cold treatments go, vitamin C is not supported by much evidence.
According to a systematic review in the Cochrane Reviews,
The failure of vitamin C supplementation to reduce the incidence of colds in the general population indicates that routine vitamin C supplementation is not justified, yet vitamin C may be useful for people exposed to brief periods of severe physical exercise. Regular supplementation trials have shown that vitamin C reduces the duration of colds, but this was not replicated in the few therapeutic trials that have been carried out.
Admittedly, the researchers did find some evidence, never in the form of a double blind or randomized clinical trial, that vitamin C may reduce the length of a cold. Additionally, they found that high performance athletes may benefit from vitamin C to prevent colds, but even there, the evidence was not one would consider to be clinically significant.
However, given the low cost of vitamin C, it probably does no harm to try it. We should all be aware that there is absolutely no evidence that it has a prophylactic effect or it will reduce the severity of the cold. Downing a handful of vitamin C every day probably will do nothing for you, unless you’re suffering from some serious vitamin C deficiency, but it probably won’t harm you either. Besides, some vitamin C supplements taste awfully good.
Oscillococcinum is a homeopathic preparation, derived from duck liver and heart (yes, you read that right), that is claimed to treat the flu. Although, the focus of this article is common cold treatments, a lot of people take this for colds, and of course, a lot of people conflate colds and flus.
Typical of many homeopathic potions, it is diluted to 200C, which means that the original substance is diluted 1 part in 100 parts of water, repeated 200 times. I’ll do the math for you – this means that there is one molecule of duck guts for every 10^55 cubic light years of water. Yes, you read that right, the odds are there isn’t a single molecule of duck guts in any oscillococinum pill you swallow.
Now, your typical woo-pushing homeopath will make a nonsense claim that water “remembers” that duck gut molecule, an effect called “water memory.” In other words, that 10^55 cubic light years of water remember the duck guts molecules. Even if that were true, and it isn’t, precisely how are duck guts related to the common cold?
It is simply implausible for us to believe that water has a “memory,” because if it did exist, we’d have to make wholesale changes to the basic principles of chemistry and quantum mechanics. Hey, science is open to overturning it’s basic principles, but there must be evidence. Extraordinary claims demand extraordinary evidence, and the evidence that “water memory” exists doesn’t qualify as evidence at all, extraordinary or otherwise.
And there isn’t any logical explanation of any possible mechanism that would allow one to conclude that duck offal has an effect on viruses. 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.” And given the lack of plausible physiological effects, don’t expect good evidence to appear out of nowhere.
According to another systematic review from Cochrane (yes, Cochrane is the world leader in systematic reviews),
There is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating the common cold. A single trial suggested that garlic may prevent occurrences of the common cold but more studies are needed to validate this finding. Claims of effectiveness appear to rely largely on poor-quality evidence.
Please don’t fall for the Argument from Ignorance logical fallacy, that is, since we can’t prove that garlic doesn’t work, that it could work. Those who are making the claim for garlic’s efficacy need to provide evidence, and according to this systemic review, they haven’t. And one poor quality trial does not qualify as evidence.
The evidence about zinc and colds are a bit more nuanced. In the opinion of a recent Cochrane review,
Zinc administered within 24 hours of onset of symptoms reduces the duration of common cold symptoms in healthy people but some caution is needed due to the heterogeneity of the data. Regarding prophylactic zinc supplementation, currently no firm recommendation can be made because of insufficient data.
That seems rather positive, except for a tiny problem. The Cochrane article was “withdrawn.” So this article is off the table as far as being positive or negative evidence.
This leads to an important point – although I have stated many times that Cochrane reviews can be an “authority” in science based medicine, I have found that sometimes they make ridiculous conclusions based on weak evidence. As I always recommend, you need to review the data, and in this case, they used only 5 small studies to come to the positive parts of the recommendation. And that’s just not a very good systematic review.
A review of Cochrane’s review (yes that happens) stated that “we are concerned that the potential threats of such biases in the review have not been considered carefully enough. We therefore feel that readers should be cautious in their interpretation of the evidence presented in owing to the possible threat of reporting and publication biases on the results of their Cochrane review.”
In another review of studies, that included only 199 patients, which examined zinc prophylaxis to prevent the common cold, the authors concluded that:
While the optimal composition of zinc lozenges and the best frequency of their administration should be further investigated, given the current evidence of efficacy, common cold patients may be encouraged to try zinc lozenges for treating their colds.
So right now, we have evidence that seems to be somewhat equivocal. There is only weak evidence supporting a small decrease in the average length of the cold. That seems like it would be worth it, since it couldn’t hurt, right?
Unfortunately, “the FDA has received more than 130 reports of loss of sense of smell associated with the use of these three Zicam products. In these reports, many people who experienced a loss of smell said the condition occurred with the first dose; others reported a loss of the sense of smell after multiple uses of the products.”
In other words, zinc has some possibly very weak efficacy, yet may destroy your sense of smell, especially in the intranasal form. That’s a bad benefit to risk ratio, especially since your sense of smell is critical for everything from determining if your food has gone bad to being warned of a natural gas leak. Given the very real and very dangerous risks, why would anyone take a potion that has limited evidence of efficacy?
The most important issue is that there is a total lack of large double blinded clinical trials that could better establish whether zinc has any effect. The research to date is at best, suggestive but far from conclusive.
But oral supplementation of zinc is useful, since a zinc deficiency (extremely rare for those who eat a balanced diet) can lead to immune system issues. But don’t think that more zinc boosts your immune system, simply that not having the proper level can be problematic.
Chinese medicinal herbs
Once again, let’s turn to a summary from Cochrane, which didn’t lend much credence to the efficacy of these products
The risk of bias was so high that the evidence did not support using any Chinese herbal preparation(s) for the common cold. Well-designed clinical trials are required.
So, nothing there.
Airborne is one of those supplements advertised on TV during the cold and flu season. Go to just about any pharmacy or grocery store, and there will be a rather prominent display somewhere, usually at checkout.
It is a dietary supplement that contains herbal extracts, amino acids, antioxidants, electrolytes, synthetic vitamins, and other ingredients that is heavily marketed to “support immune health.” As I’ve written, “supporting or boosting the immune system” is just not possible, except in very rare cases of chronic illnesses, chronic malnutrition, or medical treatments that might suppress the immune system. The immune system is very powerful and extraordinarily complex, and there simply isn’t a quick and easy way to make it work better (other than vaccinations, of course).
Just so you know, the US Federal Trade Commission, fined the manufacturer of Airborne for US$7 million for deceptive advertising, stating that “there is no competent and reliable scientific evidence to support the claims made by the defendants that Airborne tablets can prevent or reduce the risk of colds, sickness, or infection; protect against or help fight germs; reduce the severity or duration of a cold; and protect against colds, sickness, or infection in crowded places such as airplanes, offices, or schools.” So there you go, buyer beware.
Common cold treatments – real science
The common cold tends to resolve itself without external help, but there really isn’t much you can do to make your immune system attack that cold faster.
So what do you do about colds? The CDC makes the best recommendations for treating the common cold:
- Stay at home while you are sick
- Avoid close contact with others, such as hugging, kissing, or shaking hands
- Move away from people before coughing or sneezing
- Cough and sneeze into a tissue then throw it away, or cough and sneeze into your upper shirt sleeve, completely covering your mouth and nose
- Wash your hands after coughing, sneezing, or blowing your nose
- Disinfect frequently touched surfaces, and objects such as toys and doorknobs
Sure, if you want to buy some vitamin C, zinc or something else, it’s probably not going to harm you (stay away from nasal zinc). But don’t count on them to actually be useful common cold treatments. The evidence for these common cold treatments tell us that the efficacy ranges from inconclusive to absolutely useless.
Editor’s note: This article is a substantial update of an article originally published in October 2013. It includes updates to peer reviewed research, new information about some supplements, and other changes.
- Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013 Jan 31;1:CD000980. doi: 10.1002/14651858.CD000980.pub4. Review. PubMed PMID: 23440782.
- Hemilä H, Petrus EJ, Fitzgerald JT, Prasad A. Zinc acetate lozenges for treating the common cold: an individual patient data meta-analysis. Br J Clin Pharmacol. 2016 Nov;82(5):1393-1398. doi: 10.1111/bcp.13057. PubMed PMID: 27378206; PubMed Central PMCID: PMC5061795.
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- Mathie RT, Frye J, Fisher P. Homeopathic Oscillococcinum® for preventing and treating influenza and influenza-like illness.Cochrane Database Syst Rev. 2015 Jan 28;1:CD001957. doi: 10.1002/14651858.CD001957.pub6. Review. PubMed PMID: 25629583.
- Peters JL, Moreno SG, Phillips B, Sutton AJ. Are we sure about the evidence for zinc in prophylaxis of the common cold? Expert Rev Respir Med. 2012 Feb;6(1):15-6; author reply 17-8. doi: 10.1586/ers.11.84. PubMed PMID: 22283573.
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- Singh M, Das RR. WITHDRAWN: Zinc for the common cold. Cochrane Database Syst Rev. 2015 Apr 30;(4):CD001364. doi: 10.1002/14651858.CD001364.pub5. Review. PubMed PMID: 25924708.
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