The Powerful Defense of Allicin in Garlic Plants

Allicin - Dr. Axe

Plants may seem defenseless when it comes to warding off pests, rodents and other predators, but they in fact have a secret weapon: pungent smells and tastes in the form of phytochemicals, which sometimes are toxic to small creatures when ingested. Allicin, produced inside raw garlic cloves, is an example of a compound that has these effects.

Not only does it offer protection to garlic plants themselves, but allicin benefits humans in a variety of ways too. For example, studies have found that whether from eating garlic or taking allicin supplements, allicin can help treat infections, support cardiovascular function and more.

What Is Allicin?

Allicin is defined as an organosulfur compound that is obtained from garlic. Garlic cloves (Allium sativum), a species in the Alliaceae plant family, actually produce more allicin via enzymatic reactions when the plant is attacked or injured.

This compound is formed after the enzyme alliinase converts alliin to allicin.

Allicin supplements are more accurately referred to as “garlic pills,” since they contain a number of active compounds. Allicin is responsible for the signature smell and taste of garlic.

Compounds created by allicin are considered to be very volatile. They give off hydrogen sulfide, the reason they are so pungent.

How is allicin extracted from garlic? Purified allicin is actually not sold commercially because it is not very stable.

In terms of its bioavailability, allicin is considered to be an “unstable” compound because it’s only present in fresh, unheated garlic that has been cut or crushed, but not cooked. Its chemical composition changes quickly once it’s extracted and consumed as it enters the gastrointestinal tract, plus it has a very “offensive odor,” meaning few people would be willing to ingest it.

There are two main classes of organosulfur compounds found in whole garlic cloves: L-cysteine sulfoxides and γ-glutamyl-L-cysteine peptides.

Allicin breaks down to form a variety of organosulfur compounds, which are associated with protective effects. These include diallyl trisulfide (DATS), diallyl disulfide (DADS) and diallyl sulfide (DAS).

Diallyl trisulfade is more stable than allicin, so it’s used in supplements and medications for purposes such as treating bacterial, fungal and parasitic infections.


According to the Phytochemicals website, garlic contains many sulfur compounds and phytochemicals, the three most important being alliin, methiin and S-allylcysteine. Together these have been shown to have therapeutic effects, including antibacterial, antifungal, hypolipidemic, antioxidant, anticancer effects and more.

Several different types of garlic supplements are now available. Levels of organosulfur compounds that these supplements provide depends on how they were produced.

Because it has a broad range of biological activities and breaks down to form other organosulfur compounds, allicin uses include:

  • Fighting infections, due to its antimicrobial activity
  • Protecting heart health, for example due to its cholesterol- and blood pressure-lowering effects
  • Potentially helping to protect against cancer formation
  • Protecting the brain from oxidative stress
  • Warding off insects and microorganisms

Best Way to Obtain It

The very best way to obtain allicin is from eating fresh garlic that has been crushed or sliced. Fresh, uncooked garlic should be crushed, sliced, or chewed to maximize allicin production.

Heating garlic has been shown to reduce its antioxidant, antibacterial and vascular protective effects, since it changes the chemical composition of sulfur compounds. Some studies have found that during one minute in the microwave or 45 minutes in the oven, a significant amount has been lost, including almost all anticancer activity.

Microwaving garlic is not recommended. However, if cooking garlic it’s best to keep the cloves whole and to either roast, acid mince, pickle, grill or boil the garlic to help retain its nutrients.

Allowing crushed garlic to stand for 10 minutes before being cooked may help increase levels and some biological activity. However, it’s debatable how well this compound can withstand its journey through the gastrointestinal tract once eaten.

Are there any other allicin foods aside from garlic? Yes, it’s also found in onions nutrition and other species in the family Alliaceae, to a lesser extent. However, garlic is the single best source.

While it has many health-promoting characteristics, studies have not found black garlic to provide higher amounts of allicin than other types of garlic. However, eating all types of garlic is still beneficial and encouraged, since the many benefits of garlic extend beyond allicin — such as providing flavonoids, steroid saponins, organoselenium compounds and allixin.

Health Benefits

1. Possesses Antioxidant Activity

Research studies have demonstrated that allicin has antioxidant properties that can help significantly reduce oxidative stress. This means it may help protect against cellular damage, brain damage and many other age-related conditions.

2. Supports Cardiovascular Health

What are the benefits of allicin for heart health? Overall, scientific studies have provided conflicting results.

While a number of studies have found that garlic pills can have cholesterol-lowering properties, others have not found such effects.

It’s believed that the way garlic is prepared, and how allicin and other compounds are extracted, may explain this. S-allylcysteine on the other hand is bioavailable and has the ability to lower cholesterol, since it acts as an antioxidant and anti-inflammatory agent.

That said, there’s some evidence that allicin and garlic supplements can have hypolipidemic, antiplatelet and pro-circulatory effects. They may help improve cardiovascular function by lowering blood pressure, protecting against atherosclerosis (hardening of the arteries), and by reducing inflammation, lipoprotein modification and uptake of LDL “bad cholesterol.”

A 2013 meta-analysis found that garlic preparations significantly lowered total cholesterol and low-density lipoprotein (LDL)-cholesterol compared to placebo among adults with elevated cholesterol.

3. Has Natural Antibacterial Effects

Can allicin kill bacteria? There’s evidence that this phytochemical can inhibit bacteria, viruses and growth of yeasts, such as candida.

A 2014 study published in the journal Molecules states, “allicin can inhibit the proliferation of both bacteria and fungi, or kill cells outright, including antibiotic-resistant strains like methicillin-resistant Staphylococcus aureus (MRSA).”

The antimicrobial effect of allicin is due to its reaction with various enzymes, including thiol groups. Some research shows it can be used to promote ulcer healing and fight against various pathogens, such as Helicobacter pyloriS. aureausE. coli and others.

Although some women have reported using garlic cloves internally to help treat vaginal yeast infections, this is not recommended by most OBGYNs or health care providers.

4. Demonstrates Anticancer and Chemopreventive Activities

In vitro studies have shown that allicin extract is capable of inducing cell death and inhibiting cancerous cell proliferation. It’s been found to fight against the invasion and metastasis of human colon carcinoma cells.

Regularly eating garlic is associated with a reduced risk of prostate, colon and stomach cancer, according to some studies, but it’s unclear how much of a role allicin may play. Due to its low stability and poor bioavailability, more research is needed to determine how pure allicin can be used to help prevent or treat cancer.

Risks and Side Effects

What are the side effects of allicin? Garlic supplements are generally safe and well-tolerated, but some side effects are still possible.

The most common complaint after taking garlic tablets or oil is increased breath and body odor. Some also experience gastrointestinal symptoms, such as heartburn, abdominal pain, belching, nausea, vomiting, flatulence, constipation and diarrhea.

To prevent side effects, it’s best to take garlic supplements with food.

Higher doses (2,400–7,200 milligrams of garlic extract) may interact with medications including Warfarin, however moderate doses are safe to combine with most drugs.

In rare cases, uncontrolled bleeding has occurred, which is a serious condition that requires immediate attention.

Garlic may also trigger allergic responses and worsened asthma symptoms and symptoms of contact dermatitis in some people. Reactions to garlic supplements are most likely if someone is allergic to garlic itself.

Supplement Types

Experts consider the minimum effective dose for raw garlic to be a single clove, eaten with meals two or three times a day.

Consumption of raw garlic should not exceed 25 grams daily, which may potentially be toxic. This equates to about 6 large garlic cloves.

Pure allicin supplements or extracts are not sold commercially, but rather garlic supplements are. These contain a larger variety of compounds.

Different types of garlic supplements are available, including:

  • dehydrated garlic powder
  • garlic oil
  • garlic oil macerate
  • aged garlic extract

It’s still not entirely clear how the absorption and metabolism of allicin and allicin-derived compounds works, but studies show that garlic supplements can be beneficial for a variety of purposes, likely because of the interaction of different phytonutrients found in garlic.

Aged garlic extract is the only water-based garlic supplement, which makes it more bioavailable than most other forms. Aged garlic is also a popular form of garlic to use for supplementation since it does not have a strong garlic scent.

Garlic oil, while effective as a supplement, can potentially be toxic in high doses.

According to Oregon State University, “Although powdered garlic supplements do not actually contain allicin, the manufacturer may provide a value for the ‘allicin potential’ or ‘allicin yield’ of a supplement on the label.”

Alliinase is inactivated by the acidic pH of the stomach, so garlic tablets are usually enteric-coated to keep them from dissolving before they reach the small intestine. One study found that, unexpectedly, enteric coated tablets actually didn’t provide more bioavailable compounds compared to those that were not coated.


How much allicin should you take daily?

While dosage recommendations vary depending on someone’s health, the most commonly used doses (such as for supporting cardiovascular health) range from of 600 to 1,200 milligrams per day of garlic powder, usually divided into multiple doses. This should equate to about 3.6 to 5.4 mg/day of potential allicin.

Sometimes up to 2,400 mg/per day may be taken.  This amount can typically safely be taken for up to 24 weeks.

Below are other dosage recommendations based on supplement type:

  • 2 to 5 grams/day of garlic oil
  • 300 to 1,000 mg/day of garlic extract (as solid material)
  • 2,400 mg/day of aged garlic extract (liquid)


  • What is allicin? It’s a phytonutrient found in garlic cloves that has antioxidant, antibacterial and antifungal effects.
  • It’s one reason why eating garlic is linked to widespread health benefits, like cardiovascular health, better cognition, resistance to infection and other anti-aging effects,
  • The amount of allicin found in garlic quickly decreases after it’s heated and consumed, therefore it’s described as an unstable compound. However, allicin breaks down to form other beneficial compounds that are more stable.
  • Garlic/allicin benefits have been found to include fighting cancer, protecting cardiovascular health, lowering oxidative stress and inflammatory reactions, protecting the brain, and naturally fighting infections.
  • While garlic/allicin side effects are usually not serious, when supplementing with these compounds it’s possible to experience bad breath and body odor, GI issues, and rarely uncontrollable bleeding or allergic reactions.

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