Raw Garlic

📜 Historical Use

Garlic is Allium sativum, it is cultivated worldwide, and NCCIH describes it as having a long history of use both in foods and for health purposes. That dual status makes garlic unusual among the substances catalogued on this site, because most readers are already eating it before they ever consider a supplement. The recorded medicinal use is ancient and unusually specific: ancient writings from Egypt, Greece and India describe garlic's use for a variety of health problems, such as headache, pneumonia, throat conditions and gastrointestinal disorders. It is worth setting that list beside the modern one. Garlic is currently promoted as a dietary supplement for various purposes including helping to manage high blood cholesterol, high blood pressure and diabetes, preventing various types of cancer, and enhancing immune function, and it may also be used topically. Not one of the four ancient indications appears among the uses NCCIH says the evidence supports today, and the two modern uses with the best evidence behind them — cholesterol and blood pressure — are conditions the ancient sources had no way to measure. The continuity between traditional and contemporary garlic use is the plant, not the indication. Its long history is a good reason to take garlic seriously as a research subject, which the research record shows people have; it is not evidence that any particular claim printed on a label is true.

📊 What the Research Shows

This page is filed under immune support, and that is precisely where the evidence for garlic is thinnest. NCCIH notes that dietary supplements containing garlic have been promoted as boosters for the immune system, particularly during cold and flu season, and then states flatly that very little research has been done on this topic: a 2022 review identified only two studies that suggest a possible benefit, and both studies included only small numbers of people and had weaknesses in the research. Two small, weak studies is the entire evidence base for the use this page exists to describe. Where garlic has been studied properly is lipids. NCCIH says a great deal of research has been done on garlic, especially on its effects on levels of cholesterol and related lipids, and that garlic supplements may reduce total cholesterol and low-density lipoprotein (LDL) cholesterol to a small extent in people who have high blood cholesterol. A 2016 meta-analysis and review of 39 randomized controlled trials involving 2,300 participants treated for a minimum of 2 weeks found garlic reduced total cholesterol and LDL-C by 10 percent, but only if taken for more than 2 months and only in individuals with slightly elevated concentrations; NCCIH adds that the effect is modest in comparison with the effects of cholesterol-lowering drugs, and a 2023 review found the total-cholesterol reduction mostly consistent while the effect on LDL-C and HDL-C was variable. Beyond lipids the evidence thins quickly. Limited evidence suggests garlic supplements may reduce blood pressure to a small extent in people who have high blood pressure, and they may reduce blood sugar to a small extent in people with diabetes. Consuming garlic does not seem to reduce the risk of stomach cancer, and it is uncertain whether garlic influences the risk of colorectal cancer.

Crush 1-2 cloves, let sit 10 min (activates allicin), eat raw or add to food.

May cause heartburn. Thins blood.

⚠️ What happens if taken in excess:

The one clear injury signal attached to garlic concerns the raw form this page is about, and it is not a digestive complaint. NCCIH states that while some forms of garlic used topically also seem to be safe, fresh raw garlic may not be safe when used topically, and that it can cause severe skin irritation and chemical burns — a finding it supports with a systematic review of reported garlic burn injuries. Anyone who has read that crushed raw garlic can be pressed onto skin, a nail, an ear or a tooth should treat that as the real hazard here. Taken orally the picture is much milder. NCCIH reports that garlic, taken orally, has been used safely in research studies that lasted as long as 7 years. Side effects of garlic consumed orally include breath and body odor, abdominal pain, flatulence and nausea; the clinical digest adds heartburn and upset stomach, and notes specifically that these side effects can be more noticeable with raw garlic than with other preparations. Some people have allergic reactions to garlic. The other systemic concern is bleeding: taking garlic supplements may increase the risk of bleeding, which matters most around surgery and is covered under interactions. On pregnancy and breastfeeding, NCCIH states that garlic may not be safe for use during pregnancy or while breastfeeding when taken orally in amounts greater than those found in foods, and that little is known about the safety of using garlic topically during pregnancy or while breastfeeding. No hepatotoxicity, cardiotoxicity or neurotoxicity signal appears in either source read for this page.

Two interaction classes are named, and one drug is named outright. NCCIH warns that taking garlic supplements may increase the risk of bleeding and instructs readers to tell their health care providers, saying this is especially important if you are going to have surgery or if you take medicines, such as anticoagulants or aspirin, that may also affect bleeding. Anticoagulants and aspirin are therefore named drug classes and surgery is a named context of concern. NCCIH gives no washout period, so exactly how many days before an operation to stop is a question for the surgical team rather than for this page. The second interaction is more specific and much less widely repeated: the NCCIH clinical digest states that garlic has been found to interfere with the effectiveness of some drugs, including saquinavir, a drug used to treat HIV infection. Note the direction of that effect. Interference with effectiveness means a drug level pushed down rather than up, which for an antiretroviral is a treatment-failure problem rather than a side-effect problem. What neither source names is any cytochrome P450 enzyme or drug transporter. A page telling you that garlic induces CYP3A4 or affects P-glycoprotein is going further than these federal sources do, and the saquinavir finding is stated here as an observed interference, not as a mechanism. NCCIH's standing instruction applies: if you take anticoagulants, aspirin, or any other medicine, talk with your health care provider before using garlic or other herbal products, because some herbs and medicines interact in harmful ways.

1. Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol — Ried K, Frank OR, Stocks NP BMC Cardiovasc Disord (2008)[PubMed ↗]
2. Garlic supplementation increases testicular testosterone in diabetic rats — Oi Y et al J Nutr (2001)[PubMed ↗]
3. Aged garlic extract modifies cardiovascular risk factors — Budoff MJ et al J Nutr (2006)[PubMed ↗]