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© 2018 Steven Foster

A garlic monograph for the home

Latin Name: Allium sativum

Common Name: garlic

This garlic monograph provides basic information about garlic—common names, usefulness and safety, and resources for more information.


Garlic Basics

  • Garlic is the edible bulb from a plant in the lily family. It was traditionally used for health purposes by people in many parts of the world, including the Egyptians, Greeks, Romans, Chinese, Japanese, and Native Americans.
  • Currently, garlic is used as a dietary supplement for many purposes, including high blood cholesterol, high blood pressure, and the common cold, as well as in attempts to prevent cancer and other diseases.
  • Fresh garlic, garlic powder, and garlic oil are used to flavor foods. Garlic dietary supplements are sold as tablets or capsules. Garlic oil may be used topically (applied to the skin).

Garlic in Health Research

  • A great deal of research has been done on garlic, but much of it consists of small, preliminary, or low-quality studies.

Garlic Research Summary

  • There’s conflicting evidence about whether garlic lowers blood cholesterol levels. If it does, the effect is small, and low-density lipoprotein (LDL) cholesterol (the so-called “bad” cholesterol that’s linked to increased heart disease risk) may not be reduced at all.
  • Garlic may be helpful for high blood pressure, but the evidence is weak.
  • Some studies indicate that certain groups of people who eat more garlic may be less likely to develop certain cancers, such as stomach and colon cancers. However, garlic in dietary supplement form has not been shown to help reduce the risk of these cancers. The National Cancer Institute recognizes garlic as one of several vegetables with potential anticancer properties but does not recommend using garlic dietary supplements for cancer prevention.
  • There’s not enough evidence to show whether garlic is helpful for the common cold.

Garlic Safety

  • Garlic is probably safe for most people in the amounts usually eaten in foods.
  • Side effects include breath and body odor, heartburn, and upset stomach. These side effects can be more noticeable with raw garlic. Some people have allergic reactions to garlic.
  • Taking garlic may increase the risk of bleeding. If you take an anticoagulant (blood thinner) such as warfarin (Coumadin) or if you need surgery, tell your health care provider if you’re taking or planning to take garlic dietary supplements.
  • Garlic has been found to interfere with the effectiveness of some drugs, including saquinavir, a drug used to treat HIV infection.

Garlic References


PubMed Articles About Allium sativum

Source: National Center for Biotechnology Information (NCBI)[Internet]. Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information; [1988] – [cited 2018 Apr 5]. Available from:

Choudhary, PR., Jani, RD., Sharma, MS., (2018) Effect of Raw Crushed Garlic (Allium sativum L.) on Components of Metabolic Syndrome.

Metabolic syndrome consists of a group of risk factors characterized by abdominal obesity, hypertension, atherogenic dyslipidemia, hyperglycemia, and prothrombotic and proinflammatory conditions. Raw garlic homogenate has been reported to reduce serum lipid levels in animal model; however, no precise studies have been performed to evaluate the effect of raw crushed garlic (Allium sativum L.) on components of metabolic syndrome. Therefore, the present study was designed to investigate the effect of raw crushed garlic on components of metabolic syndrome. A total of 40 metabolic syndrome patients were randomly selected from the diabetic center of SP Medical College, Bikaner, Rajasthan, India. They underwent treatment with 100 mg/kg body weight raw crushed garlic 2 times a day with standard diet for 4 weeks; their anthropometric and serum biochemical variables were measured at both the beginning and the end of the study. Statistical analysis was performed using IBM SPSS version 20, and Student's paired "t" test was used to compare variables before and after treatment with garlic preparation. Raw crushed garlic significantly reduced components of metabolic syndrome including waist circumference (p < .05), systolic and diastolic blood pressure (p < .001), triglycerides (p < .01), fasting blood glucose (p < .0001) and significantly increased serum high-density lipoprotein cholesterol (p < .0001). There was no significant difference found in body mass index (p > .05) of patients with metabolic syndrome after consumption of raw crushed garlic for 4 weeks. Raw crushed garlic has beneficial effects on components of metabolic syndrome; therefore, it can be used as an accompanying remedy for prevention and treatment of patients with metabolic syndrome.

Mofrad, MD., Rahmani, J., Varkaneh, HK., Teymouri, A., Mousavi, SM., (2021) The effects of garlic supplementation on weight loss: A systematic review and meta-analysis of randomized controlled trials.

Obesity is related to increase in the incidence of morbidity and mortality. Studies have suggested anti-obesity properties of garlic; however, results are inconsistent. This systematic review and meta-analysis is done to summarize the data obtained from available randomized clinical trials on the effect of garlic supplementation on body weight, Body Mass Index (BMI), and Waist Circumference (WC). The online databases of Scopus, PubMed, Google Scholar and Cochrane library were searched until March 2018 for related publications using relevant keywords. Effect sizes of eligible studies were pooled using random-effects models. Cochran's Q-test and I index were used for assessing heterogeneity. We found 1241 records in our initial search, of which 13 randomized clinical trials (RCTs) with 15 treatment arms were included. Pooled analysis showed that garlic administration might significantly decrease WC (Weighed Mean Difference (WMD): -1.10 cm, 95% CI: -2.13, -0.07, P = 0.03, I = 0%). However, garlic intervention had no significant effect on body weight (WMD): -0.17 kg, 95% CI: -0.75 to 0.39, P = 0.54, I = 0%) and BMI (WMD: -0.17 kg/m, 95% CI: -0.52, 0.16, P = 0.30, I = 44.5%) as compared to controls. From Subgroup analysis, it was ascertained that the effect of garlic supplementation on BMI was significant in trials with duration < 12 weeks (WMD: -0.58 kg/m, 95% CI: -1.08, -0.08, I = 19.8%, P = 0.02) compared to those with higher duration (>12 weeks). The current meta-analysis results suggest that garlic supplementation seems to reduce waist circumference unlike body weight and BMI.

Sangouni, AA., Mohammad Hosseini Azar, MR., Alizadeh, M., (2020) Effect of garlic powder supplementation on hepatic steatosis, liver enzymes and lipid profile in patients with non-alcoholic fatty liver disease: a double-blind randomised controlled clinical trial.

Non-alcoholic fatty liver disease (NAFLD) includes a range of disorders from simple steatosis to non-alcoholic steatohepatitis. There is no proven drug treatment for NAFLD, and diet modification is considered part of the main line of treatment for this disease. The aim of this study was to investigate the efficacy of garlic supplementation in NAFLD patients. The effect of garlic powder supplementation on hepatic steatosis, liver enzymes and lipid profile was investigated in NAFLD patients. Ninety NAFLD patients were randomly assigned to take either a garlic powder supplement or a placebo for 12 weeks. The treatment group received four tablets of garlic daily (each tablet contained 400 mg garlic powder). The control group received four tablets of placebo (each placebo contained 400 mg starch). At the end of the study, hepatic steatosis was significantly reduced in the treatment group compared with the control group (P = 0·001). In addition, a significant decrease was seen in the serum concentration of alanine transaminase (P < 0·001), aspartate transaminase (P = 0·002), γ-glutamyltransferase (P = 0·003) as well as total cholesterol (P = 0·009), TAG (P < 0·001), HDL-cholesterol (P < 0·001) and LDL-cholesterol (P = 0·01) in the treatment group compared with the control group. No significant difference was seen between the two groups in serum concentration of alkaline phosphatase. Overall, garlic powder supplementation improved hepatic features and lipid profile among NAFLD patients.

Moosavian, SP., Arab, A., Paknahad, Z., Moradi, S., (2020) The effects of garlic supplementation on oxidative stress markers: A systematic review and meta-analysis of randomized controlled trials.

Recent studies have found that garlic supplementation can improve antioxidant status, however, there is no definitive consensus on this context. The present systematic review and meta-analysis aimed to investigate the effect of garlic supplementation on oxidative stress markers.

Panjeshahin, A., Mollahosseini, M., Panbehkar-Jouybari, M., Kaviani, M., Mirzavandi, F., Hosseinzadeh, M., (2020) Effects of garlic supplementation on liver enzymes: A systematic review and meta-analysis of randomized controlled trials.

Current evidence on the beneficial effects of garlic on liver enzymes is contradictory. Therefore, the aim of this systematic review and meta-analysis is to evaluate the effect of garlic supplementation on human liver enzymes, such as Alanine Transaminase (ALT/SGPT) and Aspartate Transaminase (AST/SGOT). To collect the required data, PubMed, Scopus, ISI Web of Science, and Google scholar databases were systematically searched from inception to June 2019. A meta-analysis was conducted using the random-effects model to evaluate the effects of garlic supplementation on ALT and AST levels. The Cochran's Q-test and inconsistency index were also used to evaluate heterogeneity among the studies. Among a total of 15,514 identified articles, six studies (containing 301 participants) met the inclusion criteria. Results of the meta-analysis showed that garlic supplementation significantly decreased AST level (Hedges' g = -0.36, 95% confidence interval [CI]: -0.72, -0.004, p = .047); whereas, it had no significant effect on ALT level (Hedges' g = -0.22, 95% CI: -0.64, 0.20, p = .310). Results showed that garlic supplementation reduced AST levels significantly; however, had no significant effect on ALT levels. Further studies are still needed to confirm the results.