Garlic has been shown to prevent atherosclerosis in a four-year double-blind trial.¹⁵ The preparation used, standardized for 0.6% allicin content, provided 900 mg of garlic powder per day. The people in this trial were 50 to 80 years old, and the benefits were most notable in women. This trial points to the long-term benefits of garlic to both prevent and possibly slow the progression of atherosclerosis in people at risk.

Garlic has also lowered cholesterol levels in double-blind research,¹⁶ though more recently, some double-blind trials have not found garlic to be effective.^17,18,19 Some of the negative trials have flaws in their design.²⁰ Nonetheless, the relationship between garlic and cholesterol-lowering is somewhat unclear.²¹

Garlic has also been shown to prevent excessive platelet adhesion (stickiness) in humans.²² Allicin, often considered the main active component of garlic, is not alone in this action. The constituent known as ajoene has also shown beneficial effects on platelets.²³ Aged garlic extract, but not raw garlic, has been shown, to prevent oxidation of LDL cholesterol in humans,²⁴ an event believed to be a significant factor in the development of atherosclerosis.

Garlic and ginkgo also decrease excessive blood coagulation. Both have been shown in double-blind²⁵ and other controlled²⁶ trials to decrease the overactive coagulation of blood that may contribute to atherosclerosis.

Numerous medicinal plants and plant compounds have demonstrated an ability to protect LDL cholesterol from being damaged by free radicals. Garlic,²⁷ ginkgo,²⁸ and guggul²⁹ are of particular note in this regard. Garlic and ginkgo have been most convincingly shown to protect LDL cholesterol in humans.

Garlic supplements, in doses ranging from 600–1,200 mg per day, have consistently been shown in randomized controlled trials to lower high blood pressure to a degree that is comparable to anti-hypertensive medications.^35,36,37 One randomized controlled trial that included 88 participants with high blood pressure found treatment with 1,200 mg of aged garlic extract daily for 12 weeks reduced systolic blood pressure by an average of 5 mmHg. The trial identified a subgroup of 29 responders to garlic therapy whose blood pressure dropped by more than 3%; in this subgroup, systolic blood pressure was reduced by an average of 11.5 mmHg and diastolic blood pressure by 6.3 mmHg.³⁸ Another trial found garlic extract lowered blood pressure in hypertensive patients with severe coronary artery disease: the trial included 56 participants with severe coronary artery disease who were given 800 mg of garlic extract per day or placebo for three months. Although the effect of garlic on blood pressure was not significant overall, in the 18 participants with baseline hypertension, garlic lowered blood pressure significantly more than placebo.³⁹ Furthermore, garlic extract has been found to reduce arterial stiffness, improve blood glucose control, lower high cholesterol levels, decrease blood clot risk, and improve gut microbial balance, and may reduce the risks of heart attack and stroke.^38,41

Fresh garlic may also help lower high blood pressure: In an open trial, 40 participants with metabolic syndrome were given raw crushed garlic in an amount based on body weight (100 mg per kg body weight twice daily). After four weeks, blood pressures were reduced, and other markers of metabolic health, including waist circumference, triglyceride levels, fasting glucose levels, and cholesterol levels were improved.⁴² A six-year observational study found those who eat the largest amount of allium vegetables such as garlic and onion were less likely to develop high blood pressure, chronic kidney disease, and cardiovascular events.⁴³

In a preliminary trial, topical application of garlic cloves was used successfully to treat warts in a group of children. A clove was cut in half each night and the flat edge of the clove was rubbed onto each of the warts, carefully cleaning the surrounding areas, so as not to spread any garlic juice. The areas were covered overnight with Band-Aids or waterproof tape and were washed in the morning. In all cases, the warts cleared completely after an average of nine weeks.⁴³ In another study, 23 people with warts applied an oil-soluble garlic extract twice a day to the warts. Complete recovery was seen in every case after one to two weeks. A water-soluble garlic extract was less effective.⁴⁴ Side effects after application of the oil-soluble extract included blistering, redness, burning, and increased pigmentation of the skin around the application area, which usually disappeared completely in one to two weeks. Zinc oxide ointment was applied to the surrounding normal skin in all cases in an attempt to prevent these side effects.