But aside from the fact that you might have heard it from your mom or a friend… are you actually aware of any evidence to back this purported remedy?
Myth, scam, or legit treatment?
Before we even dive into the human clinical studies looking at cold prevention and treatment, let’s review the alleged reasons why garlic remedies are said to help.
Some of these actually have underlying science to suggest they might be valid. Others are either completely fabricated or a gross exaggeration.
1st claim: Natural antibiotic
Many nutritional websites claim you should chew a clove of garlic to stave off the common cold. Some even allege that as a natural antibiotic, it works in a manner similar to Cipro and other prescriptions for sinus infections.
They allege you should only use fresh garlic for colds, not cooked or processed powder.
Why? Because when you crush a fresh clove of garlic, a chemical reaction occurs which releases allicin, which has the purported antibiotic properties. After it is heated or time has passed, the allicin breaks down.
Some sources recommend chewing the garlic right away, while others say it should be crushed and allowed to sit for 15 minutes while the enzymatic activity takes place to create the allicin.
Conclusion: False and irrelevant
In our review of natural antibiotics, we examined all of the studies about garlic.
Most of the studies – and there are only a few – involved infections caused by H. pylori, E. coli, and Staphylococcus aureus (aka staph infections).
Does garlic have antimicrobial properties? Yes it seems to, but its potency appears weak relative to medications and some studies concluded there was actually no antimicrobial benefit.
For those studies which suggested that garlic is a natural antibiotic, they were very clear it’s no substitute for prescription treatment (1):
“it is not potent like antibiotic Impinem”
Impinem is a type of IV antibiotic. Even if garlic did work, only sinus infections and some sore throats can be caused by bacteria.
Influenza and the cold are caused by viruses, which are not bacteria. Even potent prescription antibiotics will have zero effect against the rhinovirus, which is the most common type of virus that causes colds (2).
True, many things can help soothe and temporarily relieve the side effects of a cold, like a runny nose or a scratchy throat. But as far as addressing the root cause – the virus – something would need to have antiviral activity to even have a chance of being helpful.
To be clear so there is no confusion, nothing in existence today has been proven as a cold cure.
No prescription medications exist. So called herbal remedies which are sold over the counter like Sambucol black elderberry do have some intriguing research behind them, but they remain unproven.
For the flu, there are the oral antiviral medications Tamiflu (oseltamivir) and Relenza (zanamivir). Rapivab (peramivir) is similar but is rarely used outside of hospitals since it is administered intravenously (3). Those are the only FDA approved and medically proven flu treatments.
However one major drawback is that Tamiflu can be ineffective against the flu, as well as the similar medications (called adamantanes).
Also in order to work, treatment must begin at the start of catching the flu. There are side effects which must be weighed too, versus the potential benefit.
But even with early diagnosis and treatment, there are Tamiflu resistant flu viruses. For example, the H3N2 type of influenza A and the 2009 H1N1 are resistant to adamantanes (4).
While these medications do work against the vast majority of strains, how much they help is debated. Cochrane Database of Systematic Reviews compiled results from 46 clinical trials (20 for oseltamivir and 26 for zanamivir) and said:
“We found that both drugs shorten the duration of symptoms of influenza-like illness (unconfirmed influenza or ‘the flu’) by less than a day. Oseltamivir did not affect the number of hospitalisations, based on the data…”
Shaving off less than a day is better than no improvement, but it’s hardly impressive.
Problems such as those are why there is (7):
“…a continuing need for new anti-influenza therapy using novel targets and creative strategies.”
Even though a need exists, it doesn’t mean people should be optimistic that garlic treatments can be developed to fill that void, based on today’s research.
Conclusion: Insufficient evidence
There is research which suggests that antiviral garlic properties may exist, but the evidence is limited and mostly confined to lab experiments using viruses in a Petri dish or similar.
For example, the extract was found to have an anti-viral effect on the cytomegalovirus (CMV) in research (8). A 2016 study found it had inhibitory effects on infectious bronchitis virus (IBV) in chicken embryos (9). We didn’t see any about fighting the flu in a Petri dish.
While interesting, studies like these don’t tell us anything about whether they can help thwart viruses in the human body. Nor do we even know if garlic helps dogs, cats, or any other animal pet. These experiments used test tube or similar methods, not living and breathing animals.
3rd claim: Decongestant and expectorant
It is said that raw garlic is a natural expectorant for chest congestion, as it helps loosen mucus in your throat so you can cough it up.
How to use garlic as a decongestant for a runny nose is pretty straightforward. The home remedy instructions typically involve peeling a couple of raw cloves and thoroughly chewing one at a time for a few minutes. Swallow and then repeating with another clove.
Doing so on an empty stomach is advised against. The raw cloves are known to cause heartburn, so it wouldn’t be a good idea for some people, especially right before bed!
For the chew, some recommend first mashing and mixing with lemon juice or apple cider vinegar. The problem is that both of those liquids are highly acidic and can permanently damage your teeth’s enamel when they’re not adequately diluted.
Many add honey to make the taste more palatable, which seems like a safer bet versus ACV or lemon.
Conclusion: It might help
Among the 3 claims, this one seems to be the most plausible.
Even without looking at a clinical study, you know that feeling you get when you bite into raw garlic. The intense pungent taste can instantly trigger a sinus reaction, causing your nose to run or have a sneezing attack.
Normally that side effect would be undesirable, but when you’re sick with a cold, you want relief from severe nasal congestion. You want to be unstuffed and able to sneeze!
Pseudoephedrine works great for that, but it also can cause nasty side effects for some like a rapid heartbeat, dizziness, and anxiety.
Due to cardiac conditions, some people can’t use over the counter medications like that even if they wanted to. So the appeal of a natural remedy for this symptom has widespread appeal beyond the organic and naturopathic folks.
How does garlic help a cold by acting as a decongestant? You can’t call it a proven remedy or treatment, but according to the UCLA Center for East-West Medicine, it’s the natural compounds allicin, S-Ally cysteine, and ajoene (10). Those are believed to help with the flow of mucus in the sinuses and offer anti-inflammatory benefits.
Even if it does help with a stuffy nose, keep in mind that it’s only treating a symptom of a cold or flu. It’s not doing anything to combat the root cause – the virus. Or in the case of a sinus infection – the bacteria.
As unproven herbal remedies, both white and black garlic, as well as onions, have been used for helping with congestion in the chest. Mashing up the raw cloves and mixing them with boiling water to create a steam inhalant is one common practice.
Some like to inhale the steam by making garlic tea for strep throat, which is caused by streptococcal bacteria.
Whether it’s a virus, bacteria, asthma, or allergies causing a sore throat with congestion, just plain steam from a shower helps many people. So it’s unknown what exactly – if anything – adding garlic to the steam is doing, as no studies have been done to compare and contrast.
What the clinical studies say
Okay, so you’ve heard in a nutshell the 3 main reasons why people are peddling this herb.
Now, let’s see how those compare with the clinical studies in humans for colds and other respiratory infections.
PubMed, the government database which has tens of millions of medical literature citations, is the place which will list any and all legit studies.
Doing a search under Allium sativum (the scientific name for garlic) yields over 5,000 results and of those, 214 are clinical trials.
Filtering those further for containing the word cold, you only get 7 results. Some are not even relevant, as they mention the word cold in a different context.
Rather than cherry pick which of these to cite, the most fair and balanced way is to look at all of the studies as a whole. A meta-analysis does that. It looks at multiple past studies and analyzes the results together.
As of a decade ago, what was the opinion?
UK researchers looked at all of the past clinical trials. Not only the garlic common cold studies, but also those involving the herb as a treatment for other diseases. Their conclusion was (11):
“The literature searches identified six relevant systematic reviews and meta-analysis and double-blind randomized trials (RCT) that were published subsequently. These relate to cancer, common cold, hypercholesterolemia, hypertension, peripheral arterial disease and pre-eclampsia. The evidence based on rigorous clinical trials of garlic is not convincing.”
Benefits for blood pressure and high cholesterol were basically ruled out by them, based on the research up to that point. For all other conditions – which included the common cold – they said:
“…not enough data are available for clinical recommendations.”
So by the words “not convincing” it doesn’t seem they entirely ruled out garlic for colds, but rather that there isn’t enough clinical data on the subject.
For a meta-analysis, no one is better than Cochrane Database of Systematic Reviews. They specialize in doing these.
As of the latest review, there were 8 studies they reviewed but of those, only one qualified as being objective and passing scientific scrutiny for consideration.
That study was conducted by the University of Florida and published in 2012 in the respected Clinical Nutrition journal (15). It was also registered at ClinicalTrials.gov, something which most won’t pass muster for (16).
The University of Florida Study
Rather than just look at the common cold, they combined that disease with influenza. In terms of how often people got sick and how long they were sick, both of these illnesses were lumped together in the results.
- randomized, double-blind, and placebo controlled
- 120 healthy volunteers were recruited
- 60 were given an encapsulated aged garlic extract (dosage equal to 180 mg of allicin per day)
- 60 were given a placebo version to take daily
- Both groups took these for a 12 weeks
Variables that would affect the outcome like who got a flu shot, an individual’s personal hygiene, and demographics (age and gender) were also taken into account. Anyone with a chronic illness, that was pregnant or breastfeeding, obese (BMI above 30), or had high blood pressure (140/90 or above) was not eligible to participate.
In the group taking the garlic supplements, there were 24 instances of catching a cold or flu during. In the placebo group, it was 65 instances. That means those taking garlic had 60% fewer episodes of catching a cold or the flu.
When adding up how long people were sick, the total number of days were:
- 111 sick days for garlic supplement group
- 366 sick days for placebo group
That’s nearly 70% fewer sick days for those taking garlic. As far as how long the recovery took during each episode of sickness:
- 4.63 days of illness for garlic
- 5.63 days of illness for placebo
While this is fascinating to hear, it’s important to remember this was just one study. That’s why Cochrane Database concluded:
“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.”
That’s the last clinical study on this topic, so even today that answer remains the same.
Garlic for flu is even less researched and this appears to be the only reputable study for it. However you can’t extrapolate the results and attempt to apply them to the influenza A viruses (H1N1) or (H3N2), the influenza B viruses, or the avian bird flu (H5N1). The exact breakdown of flu cases vs. colds in the study isn’t even clear, let alone what type of flu virus each person had.
In 2016 an author from the University of Florida did publish a research paper summarizing the theorized benefits of why garlic might help the immune system (17).
Titled “Aged Garlic Extract Modifies Human Immunity,” it was published in The Journal of Nutrition, which is arguably the most prestigious peer-reviewed medical journal in this field.
The scientific theory – although unproven – is that garlic extract positively affects γδ-T and natural killer (NK) cells in the body. This is because they found a higher activation of those cells in the garlic group versus those taking placebo in the trial. The author said:
“…the immune system functions well with AGE [aged garlic extract] supplementation, perhaps with less accompanying inflammation.”
The charts from left to right are γδ-T cell proliferation, serum levels of S-allyl cysteine (SAC), and glutathione levels (GSH). In all three charts, AGE = aged garlic extract capsule group.
Fighting flu with garlic?
As mentioned, no stand-alone clinical studies exist and even if you broaden your search to everything on PubMed containing the words “Allium sativum” and “flu” or “influenza” you almost get left empty handed.
Seven results to be exact. Of those, most we’ve already addressed or their text only mentions influenza in passing, in an unrelated way.
The only other thing that seems relevant was published in 2016 by researchers in India (18):
“…in order to prevent or cure viral infection, there is need to identify new inhibitors against NA [neuraminidase]. The in silico docking approaches used in this study revealed the molecular interaction of natural ligands against NA protein which may be of interest in designing new drugs from natural sources against H1N1.”
Put in plain English, what they’re saying is that Tamiflu (oseltamivir) works by inhibiting NA in flu viruses
NA is a type of protein which is “mainly responsible for initiation of viral infection and is essential for the life cycle of H1N1.”
So if you can inhibit that protein in the virus, you might be able to prevent or treat the flu.
In their laboratory research, they looked at 13 active plant compounds which they believed might inhibit NA to at least some degree.
Those isolated compounds and the sources they used for them were:
- allicin – ginger (in crushed raw garlic, the enzyme alliinase converts alliin into allicin)
- ajoene – garlic
- andrographolide – kalmegh
- baicalin – scutellaria galericulata
- carvacrol – ajwain
- eugenol – tulsi
- menthol – mantha
- theaflavin – green tea
- catechin – green tea
- courmarin – licorice
- ursolic – tulsi
- curcumin – turmeric
- tinosporon – giloy
In their molecular docking lab experiments, the researchers claimed:
“All natural ligands [the 13 compounds listed above] were reported to block influenza infection; our docking study also revealed the in silico validation for the possible mechanism of blocking. Most of the natural ligands were found to interact with H1N1 NA protein with effective binding energy…”
But remember, that’s in a lab experiment. Just because something seems to work in a test tube, that does not necessarily mean the same would happen in the human body, with all the other biological processes involved.
Even though this research was conducted almost 2 years ago, nothing new has been published on this topic.
Does garlic fight infection and kill viruses in the body? The websites reporting that garlic cures colds and helps the flu are totally exaggerating and embellishing the research. To be blunt, they’re liars.
We have gone through the studies and as you see, there really is not much. There is not proof that garlic is good for colds and coughs or influenza.
Yes, a lab experiment suggested it may be effective against the neuraminidase protein of the flu virus, but no one knows if it would do the same in the human body.
As of today, the only thing one can honestly claim is that chewing or eating the raw cloves might benefit nasal and chest congestion, but only by loosening up mucus. That’s temporarily treating a symptom or side effect of an infection. It’s not fighting the actual virus or bacteria responsible for it.
Is it possible that in the future, after a lot more clinical trials are done, that ajoene and/or allicin will be found as being beneficial? Sure, anything is possible. But right now, there is not anywhere near sufficient research to back prevention, cure, or treatment claims which some people are making.
If – and we emphasize the if word – future studies find that using garlic when sick is helpful, it most likely will not involve typical food sources.
Yes, it would be an absolute delight to be prescribed a diet of garlic bread as a cold treatment, but that will never happen.
Why? Because the compound allicin is created by an enzyme when the raw clove is crushed. It is destroyed shortly thereafter, even while it’s still raw. Heat instantly destroys it.
That means cooked foods containing this spice won’t have allicin. This fact would also nixes the idea of using garlic tea with honey, since the boiling water would destroy any allicin present.
Even if it does work, how much garlic to consume while sick would be anyone’s guess. That clinical trial involved a dosage of “aged garlic extract” which was taken in a supplement capsule 4x per day.
That equated to a 180 mg daily dose of stabilized allicin, according to the Cochrane Database commentary. Converting that to how much fresh garlic to chew or eat would be difficult, given the instability when it is fresh, due to rapid deterioration from the enzymatic reaction.
So not only is it unknown if it even works, but with only one dosage tested, no one even knows how other amounts compare, let alone chewing or swallowing garlic cloves cold and whole.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.