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Garlic Side Effects: Keep These 8 Potential Side Effects in Mind !

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garlic side effects

The fact is that garlic offers a variety of scientifically-proven health benefits. And, those who are aware of these health benefits use garlic not only to add flavour to their meals but also to improve their health.

However, like everything garlic, too, has its pros and cons. In this article, we will discuss the potential side effects of garlic.

As the National Institutes of Health states; garlic is probably safe for most people, especially when eaten in foods and in moderation (1).

Nevertheless, in some cases, garlic may cause certain side effects, particularly when eaten raw and in excess amounts (1).


8 Potential Side Effects of Garlic

As mentioned above, garlic consumption is safe for most people. However, a specific drug you may be using, a certain medical condition you suffer from or a specific allergy you have can make you susceptible to experiencing some side effects of garlic.

In this section, we will look at the 8 potential side effects of garlic. Keep reading to find out these potential side effects.


1- Bad Breath

Although garlic-caused bad breath is not a health concern, it can be embarrassing in social interactions and may impact your social relationships.

Almost all of us know that garlic causes bad breath. Yet, what many of us don’t know is that garlic can also cause bad body odour (2), (3).

Dena Champion -Registered Dietitian Or Nutrition Professional Specialist- explains how garlic affects the body and mouth odour.

According to Champion: when the body breaks down garlic, sulfur-like compounds are produced. These compounds manifest themselves with the breath. They can also react with sweat thus changing the body odour (2).

Summary; garlic has the ability to affect both your breath and body odour.


2-  Heartburn

Doctors ( in general ) classify garlic as one of the potential heartburn-trigger foods. Therefore, if you have acid reflux, you should know that garlic intake may trigger heartburn in you.

However, it doesn’t necessarily mean that garlic will CERTAINLY trigger heartburn in you. Because a certain food that triggers heartburn in someone may not cause the same problem for another.

According to medical experts, garlic can trigger acid reflux in 2 ways. Garlic can either relax the oesophagal sphincter or increase stomach acid (4).

It is important to note: raw garlic can be more harmful than cooked one when it comes to heartburn (5).

Studies tell us that onions as well, which is a close relative to garlic, can trigger acid reflux (6).

Summary: more major and comprehensive studies are necessary to better understand this side effect of garlic. If you have GERD, avoiding garlic seems to be a wise decision. If you experience heartburn occasionally, then monitor your symptoms after eating garlic. In this way, you can find out whether garlic is a heartburn trigger for your body.


3-  Diarrhea or Gas

Garlic can bring about some gastrointestinal problems such as diarrhoea and gas. This is because garlic is high in FODMAP (7).

FODMAP (fructans) are fermentable complex carbohydrates. That means they are difficult to digest (8).

As garlic is high in FODMAP, it can potentially cause gas, bloating, diarrhoea, etc. However, these given digestive problems tend to occur when garlic is consumed in excess.

According to Healthline garlic also contain insoluble fibre, hence, may cause diarrhoea (9).

Summary: avoid eating too much raw garlic at once to avoid digestive issues away.


4-  Blood Thinning

Garlic is one of the natural blood-thinning foods. While it can be beneficial for those who have a blood-clotting problem, it may increase the risk of bleeding in some people.

Many people with blood-clotting problem use prescribed blood-thinning drugs to avoid potential complications.

Scientific studies and medical experts suggest that consuming garlic with a blood-thinning drug such as warfarin can cause harmful interactions (10), (11), (12).

As such medical experts recommend that those who use thinners (medication) should talk to their health care providers about garlic consumption (13).

Additionally, garlic may affect some patients during and after surgery due to the blood-thinning effect (13).

Summary: in light of the above-given information; it is best to talk to your health care provider about eating garlic if you have either scheduled surgery or if you use a blood-thinning drug.


5-  Asthma and Garlic

Under normal circumstances, garlic doesn’t trigger asthma attacks. On the contrary, there are studies that suggest garlic may ease asthma symptoms (14).

However, the thing can be the total opposite if you are allergic to garlic, although this allergy is quite rare.

According to Healthline; consuming garlic, or even breathing the dust from garlic can cause an asthma attack if you are allergic to garlic. And, the symptom can get worse if not interfered timely (15).

In another article, the author underlines that proteins in garlic can promote inflammation thus worsen asthma symptoms (16).

Summary: if you are allergic to garlic even breathing garlic may cause asthma attacks and related allergic reactions (15).


6- Skin Irritation

There is no case report associated with garlic consumption and skin irritation. Yet, applying garlic to the skin can cause burn-like damage (17).

According to Dr Lisa Maier from the University of Washington School of Medicine; a compound ( diallyl disulfide) present in garlic can irritate the skin and cause a burn or a rash (18).

In a study; researchers found that 8 patients developed contact dermatitis after applying fresh garlic bulbs onto their bare skin. Upon these findings; researchers recommend that people should avoid applying garlic directly to their skin as it may cause contact dermatitis and skin rashes (19).

Summary: The message is clear! Direct application of garlic to the skin can cause skin problems.


7- Liver Damage

Hearing that garlic may be harmful to the liver can be perplexing, given its proven health benefits.

At first, it is important to note that this potential side effect of garlic is not conclusive and can only be true when garlic is consumed in excessive amounts.

In a study, researchers concluded that due to the high antioxidant presence of garlic, garlic intake in high doses  can be toxic to the heart, liver and kidney (20)

In another study on rats; researchers concluded that garlic with high doses can potentially cause liver damage (21).

Summary; if you consume garlic in high doses you may damage your liver. What is the safe amount then? You can find the recommended daily garlic intake below.


8- Headaches

Here is another potential side effect of garlic. It is claimed that garlic can trigger headaches in some individuals.

Cleveland Clinic compiled a list of foods that can potentially trigger headaches. Garlic along with onion is on this list. Nevertheless, as Cleveland Clinic noted: this list was prepared based-on patient self-reports, not from scientific studies (22).

This list indicates that some people consider garlic a headache trigger.

In the meantime, a study published in the Journal of Pain Research suggests that ” heaty” foods one of which is garlic, may trigger migraines as well as tension headaches (23).

Summary; more conclusive studies are necessary to understand this potential side effect of garlic. If you often get headaches following garlic consumption, it might be a trigger for you. If this is the case, work with your doctor.


Safe Amount of Garlic to Avoid Side Effects

By now, we have looked at 8 potential side effects of garlic. While doing it we have realised that many of these potential side effects occur due to excess garlic consumption. This brings us to the question that ” what is the safe amount of daily garlic consumption?

According to the American Academy of Family Physicians consuming;

One or two cloves of raw garlic per day

¤ One 300-mg dried garlic powder tablet two to three times per day,

*   7.2 g of aged garlic extract per day

are ( general ) recommended dosages for adults.

According to WebMD: “Garlic is POSSIBLY SAFE when taken by children in doses of up to 300 mg three times daily for up to 8 weeks “.


Is it Safe to Eat Garlic on an Empty Stomach?

Eating garlic, especially raw garlic, on an empty stomach may cause some problems in some people.

Eating garlic on an empty stomach is not recommended for those who have the following conditions;

1- Acid reflux/GERD

2- Low Blood Pressure ( hypotension)

3- Diarrhoea

If you are to consume garlic on an empty stomach, at least eat it with water.


Tarkan is an experienced health writer ( currently more than 600 articles ) and also the founder of this website namely His expertise in health stems from in-depth medical research and knowledge which he obtained over the course of many years.

Tarkan enjoys sharing factual knowledge on health, psychology and nutrition. He always aims to deliver evidence-based recommendations, provide links to related scientific studies.

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