Garlic compounds and their health effects reviewed
What it found
Garlic and its sulfur compounds have been tested for many health effects, mostly in lab and animal studies, with some human trials on cholesterol, blood sugar and blood pressure.
The authors say garlic can cause stomach upset at high doses and may interact with some medicines.
What they found
Studies in people
Cholesterol and blood pressure
In human trials, garlic at doses of 300 to 600 mg per day for 12 weeks to 12 months lowered total cholesterol, triglycerides, and LDL, and raised HDL. Garlic also significantly decreased systolic and diastolic blood pressure in some studies.
Animal and lab studies
Antibacterial and antifungal effects
In lab tests, garlic extracts and allicin inhibited many bacteria and fungi, including antibiotic-resistant strains like MRSA. The effect varied with the type of extract, and some extracts showed no antibacterial effect.
Anticancer activity
In lab tests, allicin and other garlic compounds killed cancer cells, prevented their growth, and induced apoptosis. In rats, garlic powders reduced DNA damage in the liver caused by a carcinogen by 35%.
Studies in people and animals
Blood sugar in diabetes
A clinical study in people with type 2 diabetes and high lipids found that 900 mg per day of garlic pills decreased cholesterol, serum lipids, and fasting blood sugar. In diabetic mice and rabbits, garlic extracts lowered blood sugar by affecting insulin secretion.
Side effects and dosing
The generally recommended daily doses for elderly are 4 g of raw garlic, 7.2 g of aged garlic extract, or one dried garlic powder tablet two to three times per day. High doses can cause gastric agitation, and in rats, doses of 250 to 1000 mg/kg per day led to liver and lung deformities.
Other findings
Sulfur compounds in garlic
Garlic bulbs contain hundreds of phytochemicals, with sulfur compounds making up about 82% of the total garlic sulfur content. Allicin is the most biologically active sulfur compound and gives garlic its smell and taste.
What the authors conclude
“Thus, proper consideration should be taken when using garlic as a medicine for the treatment of different diseases.”
Also in their conclusions
- They conclude that garlic extracts and isolated compounds have several biological properties including anticarcinogenic, antioxidant, antidiabetic, renoprotective, anti-atherosclerotic, antibacterial, antifungal, antiprotozoal, and antihypertensive activities.
- They advise that proper consideration should be taken when using garlic as a medicine for the treatment of different diseases.
- They note that allicin can induce gastric agitation especially if administered in high doses, and that garlic affects the pharmacokinetics of antiretroviral drugs and anticoagulants.
How it was done
The authors wanted to gather the available scientific information on garlic's traditional uses, chemical makeup, how it moves through the body, and its pharmacological activities.
They reviewed published studies on garlic extracts and isolated compounds, including lab tests, animal experiments, and human trials. Human trials included people with diabetes, high cholesterol, and heart disease, using doses like 300 mg, 600 mg, or 900 mg of garlic per day for up to 12 months.
What it can’t tell you
- Many of the findings come from lab tests or animal studies, so they cannot show what happens in people.
- The human trials often used different garlic preparations and doses, so results are not consistent across all studies.
- This review cannot prove that garlic causes any health outcome, only that studies have found associations or effects.
Who paid
- Conflicts
- The authors declare no conflict of interest.
- Authors work at
- Obihiro University of Agriculture and Veterinary Medicine, Japan; Damanhour University, Egypt; Zagazig University, Egypt
The paper
- Title
- Chemical Constituents and Pharmacological Activities of Garlic ( Allium sativum L.): A Review
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- El-Saber Batiha G, Magdy Beshbishy A, G Wasef L, et al (2020). Chemical Constituents and Pharmacological Activities of Garlic ( Allium sativum L.): A Review. Nutrients. doi:10.3390/nu12030872Free full textPubMed 32213941DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error