Garlic
The kitchen bulb in capsule form, best known for blood pressure and cholesterol.
- Blood pressure
- Cholesterol
- Colds and flu
- Blood sugar
- Arteries and plaque
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is garlic?
Garlic is the bulb of Allium sativum, eaten everywhere as food and kept as a household remedy for centuries. What interests researchers is its sulphur chemistry: alliin, allicin, ajoene, the diallyl sulphides and S-allylcysteine. In capsules it comes as dried powder, odourless capsules and oil, tablets standardised on allicin, and extracts aged for months. It is among the most heavily trialled things in the aisle, and nearly all that work is about the heart.
Why do people take garlic?
Blood pressure
The thinking. Blood pressure is the commonest reason people buy garlic capsules, usually after a reading at the surgery came back higher than anyone wanted. The thinking rests on its sulphur chemistry: reviews describe allicin, the compound a crushed clove makes, as acting on blood pressure.
What research has found. Pooled analyses measured resting pressure, mostly in adults whose readings were already raised: the top number fell by roughly 4 to 7 mmHg, the bottom by 3 to 5, and one pooling found that fall only where readings were high to begin with. Two trials ran in people already on prescribed medicine, one finding nearly 12 mmHg off the top number at two capsules a day, nothing at one. A fair body of trials has looked at this, and most point the same way.
Cholesterol
The thinking. Cholesterol is the other half of why garlic sits in the heart aisle, and for many people the same appointment produced both numbers. The same chemistry is behind it: the reviews that describe allicin acting on blood pressure describe an effect on blood fats too.
What research has found. Reviews have pooled dozens of trials, the largest 108 trials and more than seven thousand adults. Total cholesterol came down most consistently, by about 0.64 mmol/L in one 21-trial pooling, with LDL following, HDL barely moving and triglycerides falling in some poolings and not others. One review pooled six trials of lipoprotein(a), a blood fat measured on its own, and found no change. The reviewers set two conditions: cholesterol raised to begin with, and garlic taken for longer than about two months. A reasonable number of trials have measured this, and most of them agree.
Colds and flu
The thinking. Garlic is a winter habit in many households, started around October in the hope of a lighter season. The thinking runs ahead of the research: reviews describe its sulphur compounds acting on bacteria and viruses in the laboratory, and on immune cells.
What research has found. A review went looking for trials and found one it could pool: 146 people took a supplement carrying 180 mg of allicin, or a placebo, daily for twelve weeks, and recorded 24 colds against 65, though recovery took much the same time. Its authors concluded that the evidence was insufficient. A separate trial followed 120 adults on an aged extract through a season, reported twice: about as many colds in both groups, but fewer symptoms and fewer days missed at work or school. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
Blood sugar
The thinking. A smaller group take garlic for blood sugar, often after a fasting reading crept up at the appointment that flagged the cholesterol. The thinking is that the chemistry described for fat also touches how the body handles sugar.
What research has found. Pooled analyses measured fasting blood sugar and HbA1c. Both came down modestly: across 27 trials and about 1,600 people HbA1c fell by roughly half a percentage point, while insulin and insulin resistance did not clearly change. The poolings in adults with type 2 diabetes found larger falls. This is one of the best-studied uses, and several reviews of trials broadly agree.
Arteries and plaque
The thinking. Some people take garlic with the arteries themselves in mind rather than the numbers describing them: if blood fats and pressure shift, the thinking goes, the vessel walls might follow.
What research has found. Four small trials, 26 to 104 people each, mostly adults at raised heart risk. One measured less calcium building up in the coronary arteries over a year on an aged extract; a second found one kind of soft plaque reduced while the other measures did not. A trial in adults with obesity measured less arterial stiffness; one in adults with type 2 diabetes found no clear difference. The studies disagree, so this is unsettled: dose, duration and who took part all seem to shift the result.
What does garlic do in the body?
A whole clove holds almost no allicin. It holds alliin, a sulphur-containing amino acid, which the enzyme alliinase turns into allicin the moment the clove is crushed. That is why the preparations are not interchangeable: powders and standardised tablets are sold on the allicin they yield, aged extracts on their S-allylcysteine.
Allicin is a reactive sulphur compound: it swaps bonds with the sulphur groups on proteins and on glutathione, the body’s own housekeeping molecule, and most of what reviews attribute to it is thought to follow from that. It does not last long, breaking down into relatives such as ajoene, the diallyl sulphides and vinyldithiins, which carry activity of their own. Reviews trace effects from there to cholesterol and sugar, to blood vessels and immune cells, and say the mechanisms and long-term effects are not fully understood.
What do people say about taking garlic?
These are anecdotes people have shared, not evidence.
What people like
- These threads are few, and most of the accounts come from one diabetes community, so the patterns here are thin.
- Several describe taking one tablet a day for years, one for more than two decades, as a heart habit rather than for anything they feel.
- A few say their blood pressure or cholesterol readings sit where they want them, while adding that they cannot tell whether garlic is why.
- Some start tablets two to four weeks before a summer holiday hoping to be bitten less; whether it helps divides them.
Common complaints
- Breath and garlic burping are the commonest complaint, and the usual reason given for stopping in the first weeks.
- Several say they noticed nothing at all, and one describes doubling the daily tablet after the label dose changed nothing.
- Blood thinning is the worry that recurs: two people in one thread raise it, one describing nosebleeds that settled once the tablets stopped.
How people take it
- One tablet a day at breakfast is the common pattern, usually taken alongside other supplements rather than on its own.
- People compare products by the allicin figure on the label, and quote the milligrams when they describe what they take.
- Coated and odourless versions are the usual answer to the breath problem; for colds, most reach for a raw clove instead.
Read from these public discussions:
- Garlic tablets (Diabetes Forum, 2011)
- Garlic supplement (Diabetes Forum, 2012)
- Garlic - allicin (Diabetes Forum, 2018)
- Surefire mosquito repellents (Mumsnet, 2024)
- What are the best mosquito repellants (Mumsnet, 2008)
- I need to head off this cold (Mumsnet, 2025)
What forms of garlic are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| Aged garlic extract | Garlic matured for months at controlled temperature and humidity; labelled by its S-allylcysteine, not allicin. | not in our price tables yet |
| Allicin-standardised | Standardised on allicin, the compound alliin turns into when a clove is crushed. | not in our price tables yet |
| Garlic powder | Dried, ground clove pressed into tablets or capsules; odourless versions and garlic oil sit in this group. | 18 mg to 100 mg |
What else is worth knowing about garlic?
- Labels give the amount per serving, which may be more than one tablet, and the figure counts different things by preparation: powders and allicin-standardised tablets on the allicin they yield, aged extracts on their S-allylcysteine. Trials used 400 mg powder tablets, or 240 to 960 mg of aged extract.
- Odour is a reported side effect, not only a social one: the single trial the cold review could pool listed rash and odour as its unwanted effects. The blood pressure reviews recorded none serious, a dose-finding trial put tolerability and acceptability at 93 per cent, highest at one or two capsules a day, and one trial report notes that tolerance of ordinary preparations is low, which is why aged extracts were developed.
- Most trials recruited adults who already had something to move — raised cholesterol, high blood pressure, type 2 diabetes, extra weight — and the largest review found the changes clearest in those whose starting figures were poorest.
- Preparations part company in the research: one lipid review found garlic oil lowered cholesterol more than garlic powder did, and a pooling of aged garlic alone moved the top blood pressure number but not the bottom.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (36 studies)
- The Effect of Aged Garlic Supplementation on Blood Pressure and Lipid Profile: A Dose-Response Grade-Assessed Systematic Review and Meta-Analysis of Randomized Controlled Trials. (2025, meta-analysis)
- Garlic: A systematic review of the effects on cardiovascular diseases. (2023, systematic review)
- Garlic Lowers Blood Pressure in Hypertensive Individuals, Regulates Serum Cholesterol, and Stimulates Immunity: An Updated Meta-analysis and Review. (2016, meta-analysis)
- Effect of garlic on blood pressure: a meta-analysis. (2015, meta-analysis)
- Garlic for hypertension: A systematic review and meta-analysis of randomized controlled trials. (2015, meta-analysis)
- Antihypertensive Effects of an Optimized Aged Garlic Extract in Subjects with Grade I Hypertension and Antihypertensive Drug Therapy: A Randomized, Triple-Blind Controlled Trial. (2023, randomised trial)
- Effects of an Optimized Aged Garlic Extract on Cardiovascular Disease Risk Factors in Moderate Hypercholesterolemic Subjects: A Randomized, Crossover, Double-Blind, Sustainedand Controlled Study. (2022, randomised trial)
- Aged garlic extract reduces blood pressure in hypertensives: a dose-response trial. (2013, randomised trial)
- Effects of Garlic Supplementation on Cardiovascular Risk Factors in Adults: A Comprehensive Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials. (2026, meta-analysis)
- Effect of garlic on the components of metabolic syndrome: A systematic review and meta-analysis of randomized controlled trials. (2024, meta-analysis)
- Garlic consumption can reduce the risk of dyslipidemia: a meta-analysis of randomized controlled trials. (2024, meta-analysis)
- Effect of garlic extract on markers of lipid metabolism and inflammation in coronary artery disease (CAD) patients: A systematic review and meta-analysis. (2023, meta-analysis)
- Anti-hyperlipidemia of garlic by reducing the level of total cholesterol and low-density lipoprotein: A meta-analysis. (2018, meta-analysis)
- Effect of garlic on plasma lipoprotein(a) concentrations: A systematic review and meta-analysis of randomized controlled clinical trials. (2016, meta-analysis)
- An umbrella review of garlic intake and risk of cardiovascular disease. (2016, systematic review)
- Effect of garlic on serum lipids: an updated meta-analysis. (2013, meta-analysis)
- 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. (2020, randomised trial)
- Effect of Raw Crushed Garlic (Allium sativum L.) on Components of Metabolic Syndrome. (2018, randomised trial)
- Reduction of blood lipid parameters by a 12-wk supplementation of aged black garlic: a randomized controlled trial. (2014, randomised trial)
- Garlic for the common cold. (2014, systematic review)
- Aged Garlic Extract Modifies Human Immunity. (2016, randomised trial)
- Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention. (2012, randomised trial)
- Effects of garlic supplementation on glycemic indices in adults: a GRADE-assessed systematic review and dose-response meta-analysis of randomized controlled trials. (2026, meta-analysis)
- Effects of Garlic on Glucose Parameters and Lipid Profile: A Systematic Review and Meta-Analysis on Randomized Controlled Trials. (2024, meta-analysis)
- The effect of garlic on lipid profile and glucose parameters in diabetic patients: A systematic review and meta-analysis. (2019, meta-analysis)
- Effects of garlic powder supplementation on insulin resistance, oxidative stress, and body composition in patients with non-alcoholic fatty liver disease: A randomized controlled clinical trial. (2020, randomised trial)
- The effect of aged garlic extract on the atherosclerotic process - a randomized double-blind placebo-controlled trial. (2020, randomised trial)
- Garlic extract favorably modifies markers of endothelial function in obese patients -randomized double blind placebo-controlled nutritional intervention. (2018, randomised trial)
- Aged Garlic Extract Reduces Low Attenuation Plaque in Coronary Arteries of Patients with Metabolic Syndrome in a Prospective Randomized Double-Blind Study. (2016, randomised trial)
- The effects of garlic extract upon endothelial function, vascular inflammation, oxidative stress and insulin resistance in adults with type 2 diabetes at high cardiovascular risk. A pilot double blind randomized placebo controlled trial. (2016, randomised trial)
- Chemical Constituents and Pharmacological Activities of Garlic ( Allium sativum L.): A Review. (2020, review)
- Bioactive Compounds and Biological Functions of Garlic ( Allium sativum L.). (2019, review)
- Allicin: chemistry and biological properties. (2014, review)
- Antibacterial Properties of Organosulfur Compounds of Garlic ( Allium sativum ). (2021, review)
- Antiviral potential of garlic ( Allium sativum ) and its organosulfur compounds: A systematic update of pre-clinical and clinical data. (2020, review)
- Garlic: a review of potential therapeutic effects. (2014, review)
How much does garlic cost?
That depends on the form and the pack, so we work out the price of the same dose of every garlic product we can find and rank them.