Garlic is a sterile crop. A genome study calls it entirely sterile and clonally propagated. So the bulbs sold today are copies grown from cloves, not from seed. The same work finds that the two groups of garlic grown in China were domesticated along independent routes.
A whole clove holds no ready-made allicin, the compound behind garlic’s smell. Allicin forms from a precursor called alliin and an enzyme called alliinase when the clove is damaged, as in crushing or chewing.
In a lab test, crushing garlic before cooking kept more of its anti-clotting activity. In a rat study, letting crushed garlic stand for 10 minutes before a short microwave blast kept its anticancer effect. No study in people shows that waiting changes health, so treat the 10 minutes as a cheap habit, not a proven trick.
Garlic is eaten by the clove, not the cup. One clove (3 g) has about 4 calories and 0.2 g of protein. It gives 2% of the Daily Value, the FDA’s daily target, for vitamin B6 and for manganese. So the research is about its sulfur compounds, not its vitamins.
Most of those studies used garlic powder tablets, aged garlic extract or other supplements, and each card below says which.
Health benefits of garlic
The top findings from 29 studies, strongest evidence first
What the stars mean
- Strong. Several randomized trials, pooled in a meta-analysis, point the same way, or regulators (FDA or EFSA) have approved the claim.
- Moderate. Good randomized trials support it, but there are fewer of them, or their results vary.
- Limited. Small, short or single trials, or mixed results. Promising, but it needs confirmation.
Population and lab studies get no stars: they show a link or a mechanism, not proof.
How we rate evidence →- ★★★Lower blood pressure, from supplementsThe top number fell a little (5.1 mm Hg systolic) across 20 trials, and more in people with high blood pressure (8.7 mm Hg). These were supplements, not garlic cooked in meals.
- ★★Lower cholesterol with supplements, unclear for raw garlicPooled trials found garlic preparations lowered total cholesterol by 17 mg/dL in people with levels above 200 mg/dL after more than 2 months. In one trial of adults with moderately high LDL, about one raw clove a day did not lower LDL.
- ★★Lower average blood sugar (HbA1c)Pooled trials found garlic lowered HbA1c, a measure of average blood sugar, by 0.66. Results varied a lot between trials.
- ★Mixed, weak results on coldsIn one small trial, a garlic capsule went with 24 colds against 65 on placebo, though colds were self-reported. Aged garlic extract did not change the number of colds.
- Population studyLinked to lower lung cancer riskA Chinese study compared 399 people with lung cancer and 466 without. Raw garlic twice a week or more went with about half the risk (adjusted odds ratio 0.50), though this cannot show garlic caused it.
All 29 studies, strongest evidence first
Garlic supplements lowered systolic blood pressure by 5.1 mm Hg
This meta-analysis pooled 20 randomized trials (970 people) of garlic preparations against placebo. Systolic pressure fell 8.7 mm Hg in people with high blood pressure, and diastolic pressure 2.5 mm Hg overall. In the trials of people who started at 140/90 mm Hg or higher, diastolic pressure fell 6.1 mm Hg. The author’s conclusions speak of garlic supplements, not garlic in meals, and the paper also reviews cholesterol and immunity.
Garlic supplements lowered systolic pressure by 3.75 mm Hg in 17 trials
This meta-analysis pooled 17 randomized trials, most against placebo, and diastolic pressure fell 3.39 mm Hg compared with controls. The systolic drop held in people with high blood pressure (4.4 mm Hg) but not in people with normal pressure. Diastolic results varied between trials until the outliers were removed. That left a 2.68 mm Hg drop in people with high blood pressure.
Garlic extracts lowered systolic pressure by 8.1 mm Hg in hypertension
This meta-analysis pooled 12 reports from placebo-controlled trials, with 405 people on garlic derivatives and 333 on placebo. Diastolic pressure fell about 4 mm Hg. The authors say a trial sequential analysis shows enough trials already exist. The abstract does not say which garlic forms were pooled.
Raw garlic, about one 4 g clove daily, did not lower LDL
This randomized trial included 192 adults with moderately high cholesterol (LDL of 130 to 190 mg/dL). They ate raw garlic or took garlic powder tablets, aged garlic extract capsules or a placebo, 6 days a week. After 6 months LDL had risen 0.4 mg/dL on raw garlic and fallen 3.9 mg/dL on placebo. None of the forms, each dosed like an average clove, changed HDL, triglycerides or the ratio of total to HDL cholesterol.
Garlic preparations lowered high total cholesterol by 17 mg/dL
This meta-analysis pooled 39 trials of garlic preparations. The drop was in people with levels above 200 mg/dL who used garlic for longer than 2 months. In the same group LDL cholesterol fell 9 mg/dL, HDL improved only slightly and triglycerides did not clearly change. Earlier meta-analyses had conflicting results, and the abstract does not separate raw garlic from supplements.
Garlic lowered LDL cholesterol by 0.44 mmol/L across 21 trials
This meta-analysis pooled 21 randomized trials in people with dyslipidemia (unhealthy blood fat levels). Total cholesterol fell 0.64 mmol/L and triglycerides 0.17 mmol/L, with larger drops in people over 50. Garlic oil lowered total cholesterol and LDL more than garlic powder, so the result depends on the form.
Garlic lowered HbA1c, fasting blood sugar and LDL cholesterol
This meta-analysis pooled randomized trials of garlic and garlic supplements published through February 2024. HbA1c, a measure of average blood sugar, fell by a mean difference of 0.66, and HDL rose 2.06, while triglycerides did not change. HbA1c results varied from trial to trial (I² of 62.9%), and the abstract does not give the number of trials.
Garlic lowered systolic pressure 9.1 mm Hg, less in the best trials
This meta-analysis pooled 9 double-blind trials (482 people with hypertension) of garlic preparations lasting 8 to 26 weeks. Results varied widely between trials (I² of 71%), and the diastolic drop was 3.8 mm Hg overall. Limiting the analysis to higher-quality trials shrank the systolic effect and removed the variation. The authors say the evidence is not strong and a longer, larger trial is needed.
Aged garlic lowered systolic pressure by 2.49 mm Hg, a small drop
This meta-analysis pooled 19 randomized trials of aged garlic in various forms. LDL cholesterol fell 4.41 mg/dL, also a small drop. Diastolic pressure and HDL did not clearly change, and the 4.74 mg/dL drop in total cholesterol fell just short of being clear. Cholesterol results differed a lot between trials (I² of 74.8%).
Tzatziki with 4.2 g raw garlic did not impair platelet function
In this randomized crossover trial, 18 healthy volunteers ate Greek tzatziki with or without raw garlic, and blood was tested 5 hours later. Five volunteers also ate 4.2 g of raw garlic a day for 1 week, with the same result. The authors judge dishes with this much garlic unlikely to raise bleeding risk in surgery. They say combinations with platelet-inhibiting drugs need more study.
10 sliced garlic cloves in meals had no effect on H. pylori
This crossover study tested 12 adults infected with H. pylori, a stomach bacterium, with a breath test. They ate meals with 10 sliced cloves of fresh garlic, six jalapeños, bismuth subsalicylate (the positive control) or nothing added. Only bismuth lowered the signal. The authors warn that results from test tubes do not always carry over to people.
5 g raw garlic raised activity of 7 immune and cancer genes
In this randomized crossover trial, 17 volunteers ate a single meal of bread and butter with or without the crushed garlic. Blood was drawn 3 hours later, and gene activity rose 1.6 to 3.0 times. It measured gene activity, not illness, so it is a clue to how garlic acts, not proof of a health effect.
Raw garlic was followed by lower blood pressure, triglycerides and blood sugar
In this before-and-after study, 40 people with metabolic syndrome (a cluster of heart risk factors) ate raw crushed garlic twice a day for 4 weeks. There was no placebo group, so the changes cannot be pinned on garlic. Each dose, taken twice a day, was 100 mg per kilogram of body weight, several cloves a day for most adults. Fasting blood sugar fell, HDL cholesterol rose and waist size fell, while body mass index did not change.
Boiled gave 16%, roasted 30%, of crushed raw garlic’s allicin marker
This bioassay in 13 people compared 13 garlic supplements and 9 garlic foods with crushed raw garlic. The researchers tracked allyl methyl sulfide, the main breath marker of allicin, for 32 hours; black garlic gave only 5%. Kwai garlic powder tablets gave 80%, while enteric-coated tablets ranged from 36 to 104% and fell to 22 to 57% with a high-protein meal. It measured a marker, not health outcomes.
Garlic powder tablets did not lower cholesterol in 12 weeks
In this double-blind placebo-controlled trial, 50 people with high cholesterol at 2 clinics took Kwai garlic powder (28) or a placebo (22). The dose, 900 mg a day, equals about 1 clove of fresh garlic. Neither group had clear changes in total, LDL or HDL cholesterol or triglycerides.
Garlic powder tablets did not change cholesterol, blood pressure or artery stiffness
In this double-blind placebo-controlled trial, 75 healthy adults aged 40 to 60 with normal cholesterol took the tablets for 12 weeks. Of them, 62 were in the main analysis. The dose, 10.8 mg of alliin a day, matches about 3 garlic cloves. Triglycerides were 12% lower on garlic, but the difference could be chance.
Cochrane review: only one trial of garlic for colds
This review of randomized trials of garlic for preventing or treating colds flagged 8 trials and kept one, too little to judge. In it, 146 people took a garlic supplement with 180 mg of allicin content or placebo for 12 weeks. There were 24 colds on garlic and 65 on placebo, self-reported, and rash and odor were side effects. The authors say claims of benefit rest largely on poor-quality evidence.
An allicin capsule daily cut reported colds from 65 to 24
This is the one trial the Cochrane review above counted: a placebo-controlled survey of 146 volunteers over 12 weeks. Volunteers kept daily diaries between November and February. Symptoms lasted 1.52 days on garlic against 5.01 on placebo. Colds were self-reported and the sample was small.
Aged garlic extract: 21% fewer reported symptoms, but not fewer colds
In this placebo-controlled trial, 120 healthy adults took 2.56 g a day of encapsulated aged garlic extract for 90 days. The number of colds and flu did not change. Days of reduced functioning were 61% fewer and missed work or school days 58% fewer. These were secondary outcomes tested with a simple z-test, and immune cells multiplied better after 45 days.
Two aged garlic capsules daily lowered systolic pressure by 11.8 mm Hg
In this double-blind placebo-controlled trial, 79 general-practice patients with uncontrolled hypertension took 1, 2 or 4 capsules a day for 12 weeks. That is 240, 480 or 960 mg, added to their usual blood pressure medicine. Four capsules gave a borderline result (7.4 mm Hg). One capsule, and diastolic pressure, showed no clear change.
Garlic extract and oil did not clearly lower stomach cancer cases
This randomized placebo-controlled trial took place in Linqu County, China, a high-risk region. Its 3,365 residents took garlic extract and oil or a placebo for 7.3 years and were followed for 22 years. Garlic gave 0.81 times the odds of cases, and stomach cancer deaths were borderline lower (0.66 times the risk). The same trial tested treatment for H. pylori and vitamins, and vitamins lowered cases.
Highest garlic intake: 20% lower colorectal cancer risk, not in cohorts
This meta-analysis pooled 11 studies (12,558 cases). Case-control studies gave 0.71 times the risk and cohort studies 0.99, and results varied a lot (I² of 68.3%). Case-control studies compare people with and without the disease and depend on people recalling past diet.
Garlic was not linked to stomach cancer in two US cohorts
These cohorts followed 77,086 women and 46,398 men for up to 30 years, with 292 stomach cancers. Eating garlic 5 or more times a week against never gave 1.39 times the risk, a gap that could be chance. The authors say the findings do not support high garlic intake lowering the risk.
Moderate garlic in food went with 30% lower colorectal cancer risk
This cohort followed 58,508 US adults aged 55 to 74 for a median 12.05 years, with 782 cases. The pattern was U-shaped, with no trend across intake groups, and clearer in men than in women. Food questionnaires are imperfect.
Frequent raw garlic tied to half the lung cancer risk
This Chinese case-control study interviewed 399 people with lung cancer and 466 healthy controls in Taiyuan. Eating raw garlic less than twice a week gave an adjusted odds ratio of 0.56, and twice a week or more 0.50. People recall past diet imperfectly, and the study cannot show that garlic caused the difference.
In women, raw garlic went with 28% lower risk of depressive symptoms
This cohort followed 7,427 adults in Tianjin, China, for a median 2 years, with 1,070 cases of depressive symptoms on a self-rating scale. In women, the lower risk was at 2 to 3 times a week. In men eating raw garlic 4 or more times a week, the risk was 1.31 times, a result that could be chance. Follow-up was short.
Allium vegetables showed no colorectal cancer link; supplements, 18% higher risk
This meta-analysis pooled 8 prospective studies of allium vegetables, the garlic and onion family (5,458 cases), and 5 of garlic supplements (2,685 cases). The risk was 1.06 times for vegetables and 1.18 times for supplements, a result the authors say needs outside validation.
Resting crushed garlic before microwaving kept its anticancer activity in rat cells
This was lab and animal work, not people. As little as 60 seconds of microwaving or 45 minutes of oven heating blocked an effect of garlic in rat breast cells. Garlic normally stops a cancer-causing chemical from binding to DNA there. Letting crushed garlic stand for 10 minutes before 60 seconds of microwaving prevented the total loss, in line with heat inactivating the enzyme alliinase.
Crushing garlic before cooking kept some of its anti-clotting activity
This lab test of garlic extracts used human blood platelets, not people. Oven heating at 200°C or boiling for 3 minutes or less did not reduce the effect. Six minutes wiped it out in uncrushed garlic but not fully in crushed garlic, and more than 10 minutes wiped it out in both. Allicin levels tracked the activity.
Who should be careful with garlic
Most people can eat garlic freely. Take a little care if one of these applies:
- Blood thinners, aspirin or surgery. The NIH’s National Center for Complementary and Integrative Health says garlic supplements may increase the risk of bleeding. It says to tell your health care providers, especially before surgery or if you take anticoagulants or aspirin. For garlic in food the concern looks small: 4.2 g of raw garlic in a dish did not impair platelet function in 18 volunteers.
- Irritable bowel syndrome. Monash University lists garlic as high in fructans, a FODMAP that can cause bloating, cramping, gas or diarrhea in sensitive people. Garlic-infused oil is low in FODMAPs because fructans dissolve in water, not in fat.
- Allergy and skin. Some people are allergic to garlic, and the NIH warns that fresh raw garlic on the skin can cause severe irritation and chemical burns. Eating it can cause breath and body odor, abdominal pain, gas and nausea.
How to choose, store and eat garlic
- Raw and crushed: crushing or chewing forms allicin. In a trial of 192 adults, raw garlic at about one 4 g clove a day for 6 months did not lower LDL cholesterol.
- Cooked: boiled garlic gave 16% and roasted garlic 30% of the allicin marker that crushed raw garlic gave. Crushing first and waiting about 10 minutes before a short blast of heat kept activity in lab and rat tests. No human trial has tested it.
- Supplements and oil: most trials used tablets or extracts, and forms differ. Kwai powder tablets gave 80% of raw garlic’s allicin marker, enteric-coated tablets 36 to 104%. Garlic-infused oil is low in FODMAPs, but garlic in oil at room temperature is a botulism risk. The UC guide says to freeze it instead.
Pick firm, tight-skinned heads, and store them in a cool, dry, well-ventilated place such as a mesh bag. There they keep 3 to 5 months at about 60°F (16°C).
Cooking changes the flavor: the sharp bite comes from a reaction that cannot happen after garlic is cooked. That is why roasted garlic tastes sweet. Garlic is a low-acid food, and at least three botulism outbreaks in North America were linked to garlic-in-oil mixtures.
Sources
- Garlic: usefulness and safety. National Center for Complementary and Integrative Health, NIH.
- All about onion, garlic and infused oils on the low FODMAP diet. Monash University FODMAP blog. 2023.
- Harris LJ. Garlic: safe methods to store, preserve, and enjoy. University of California Agriculture and Natural Resources, publication 7231. 1997.
- Gardner CD, Lawson LD, Block E, et al. Effect of raw garlic vs commercial garlic supplements on plasma lipid concentrations in adults with moderate hypercholesterolemia. Arch Intern Med. 2007.
- Scharbert G, Kalb ML, Duris M, et al. Garlic at dietary doses does not impair platelet function. Anesth Analg. 2007.
- Lawson LD, Hunsaker SM. Allicin bioavailability and bioequivalence from garlic supplements and garlic foods. Nutrients. 2018.
- Song K, Milner JA. The influence of heating on the anticancer properties of garlic. J Nutr. 2001.
- Cavagnaro PF, Camargo A, Galmarini CR, Simon PW. Effect of cooking on garlic (Allium sativum L.) antiplatelet activity and thiosulfinates content. J Agric Food Chem. 2007.
History of garlic
Garlic began in the mountains of Central Asia, according to a 2023 genome study of 41 garlic accessions from different regions. As it spread, people selected types for different climates, and along the way it lost fertility and seed production.
Cuneiform records show garlic grown in Mesopotamia for at least 4,000 years. Well-preserved garlic was found in the tomb of Tutankhamun, dated to about 1325 BC. A review of its medical history says garlic turned up in Egyptian pyramids and ancient Greek temples. Medical texts from Egypt, Greece, Rome, China and India all prescribed it, the review says.
Garlic was also working food. Ancient Greek and Roman soldiers and sailors ate it. The Hebrew Bible says the Israelites in the wilderness missed the garlic they had eaten in Egypt. The same review reports that garlic was given to the original Olympic athletes in Greece, perhaps one of the earliest performance-enhancing foods.
In Central European folk belief, garlic warded off demons, werewolves and vampires, so people hung it in windows and rubbed it on keyholes. Its strong smell also earned it the nickname “stinking rose”.
Today garlic is a global crop. World production was about 30 million tonnes in 2024, and China grew 73% of it, according to FAOSTAT figures quoted by Wikipedia.
Sources
- Shemesh-Mayer E, Faigenboim A, Sherman A, et al. Deprivation of sexual reproduction during garlic domestication and crop evolution. Int J Mol Sci. 2023.
- Li N, Zhang X, Sun X, et al. Genomic insights into the evolutionary history and diversification of bulb traits in garlic. Genome Biol. 2022.
- Rivlin RS. Historical perspective on the use of garlic. J Nutr. 2001.
- Borlinghaus J, Foerster J, Kappler U, et al. Allicin, the odor of freshly crushed garlic: a review of recent progress in understanding allicin’s effects on cells. Molecules. 2021.
- Garlic. Wikipedia.
Frequently asked questions about garlic
Is garlic good for you?
For most people, yes, in the amounts used in cooking. One clove (3 g) has about 4 calories. The best evidence is a small drop in blood pressure from supplements: five meta-analyses found systolic pressure fell by between 2.49 and 9.1 mm Hg. Raw garlic, about one 4 g clove a day, did not lower LDL cholesterol in a 192-person trial, so kitchen-clove benefits are unproven.
Does garlic lower blood pressure?
Garlic supplements do, a little. A meta-analysis of 20 trials found systolic pressure 5.1 mm Hg lower, and 8.7 mm Hg lower in people with high blood pressure. Another, of 9 trials, said the evidence is not strong because results varied and the best-designed trials showed smaller drops. Garlic is no replacement for blood pressure medicine, so talk to your clinic before changing treatment.
Does garlic lower cholesterol?
Slightly in some supplement trials, and not reliably. A meta-analysis of 39 trials found total cholesterol 17 mg/dL lower in people above 200 mg/dL after more than 2 months. But raw garlic, garlic powder and aged garlic extract all failed to change LDL in a 192-adult trial. A 50-person trial of garlic powder tablets also found nothing.
Is raw or cooked garlic healthier?
No trial here compared raw and cooked garlic for health outcomes; crushed raw garlic forms the most allicin. In 13 people, boiled garlic gave 16% and roasted garlic 30% of the allicin marker that raw garlic gave. In lab tests, crushing garlic before cooking kept more activity. Letting it stand 10 minutes before 60 seconds of microwaving prevented the full loss in rat cells.
How much garlic can you eat a day?
No study here sets an ideal amount. The raw garlic trials used about one 4 g clove a day for 6 months and 4.2 g of raw garlic in a dish. The NIH says garlic by mouth has been used safely in research studies lasting up to 7 years. Side effects include breath and body odor, abdominal pain, gas and nausea, and people with irritable bowel syndrome may tolerate less.
Does garlic help with colds?
The evidence is thin: a Cochrane review found one trial that qualified. In it, 146 people taking a garlic supplement with 180 mg of allicin content reported 24 colds against 65 on placebo. The review says colds were self-reported and claims rest largely on poor-quality evidence. A trial of aged garlic extract in 120 adults found no difference in how many colds people caught.
Does garlic thin your blood?
Garlic supplements may, and the NIH says to tell your care team about them before surgery or if you take anticoagulants or aspirin. For garlic in food the risk looks small: a dish with 4.2 g of raw garlic did not impair platelet function in 18 volunteers. If you take warfarin or another blood thinner, ask your clinic before adding supplements.
How many calories are in a clove of garlic?
About 4 calories in one clove (3 g), with 0.2 g of protein, 0.9 g of net carbs and 0.1 g of fiber. A clove gives 2% of the Daily Value for vitamin B6 and for manganese, which is small because so little is eaten. Gram for gram, garlic is rich in vitamin B6, with only 2 of 131 foods on this site holding more.