Numerous controlled trials have examined the effects of oral garlic on serum lipids. Long-term effects on lipids or cardiovascular morbidity and mortality remain unknown. Other preparations (such as enteric-coated or raw garlic) have not been well studied.
Small reductions in blood pressure (<10mmHg), inhibition of platelet aggregation, and enhancement of fibrinolytic activity have been reported, and may exert effects on cardiovascular outcomes, although evidence is preliminary in these areas.
Numerous case-control/population-based studies suggest that regular consumption of garlic (particularly unprocessed garlic) may reduce the risk of developing several types of cancer, including gastric and colorectal malignancies. However, prospective controlled trials are lacking.
Multiple cases of bleeding have been associated with garlic use, and caution is warranted in patients at risk of bleeding or prior to some surgical/dental procedures. Garlic does not appear to significantly affect blood glucose levels.
Aged garlic extract (AGE), ajoene, alisat, alk(en)yl thiosulfates, allicin, Allicor®, Allii sativi bulbus, alliinase, allium, allitridium, allyl mercaptan, alubosa elewe, Amaryllidaceae (family), ayo-ishi, ayu, banlasun, camphor of the poor, clove garlic, da-suan, dai toan, dasuan, dawang, diallyl, diallyl disulphide (DADS), diallyl sulfide (DAS), diallyl sulphide, diethyl disulfide, diethyl hexasulfide, diethyl monosulfide, diethyl pentasulfide, diethyl tetrasulfide, diethyl trisulfide, dipropyl disulphide, dipropyl sulphide, dra thiam, (E)-ajoene, foom, garlic clove, garlic corns, garlic extract, garlic oil, garlic powder extract, Gartenlauch, hom khaao, hom kia, hom thiam, hua thiam, Karinat® (beta-carotene 2.5mg, alpha-tocopherol 5mg, ascorbic acid 30mg and garlic powder 150mg per tablet), kesumphin, kitunguu-sumu, knoblauch, kra thiam, Krathiam, krathiam cheen, krathiam khaao, Kwai®, Kyolic®, l'ail, lahsun, lai, la-juan, lasan, lashun, la-suan, lasun, lasuna, lauch, lay, layi, lehsun, lesun, Liliaceae (family), lobha, majo, methyl allyl, naharu, nectar of the gods, Ninniku, pa-se-waa, poor man's treacle, rason, rasonam, rasun, rust treacle, rustic treacles, S-alk(en)yl cysteine sulfoxide, S-allylcysteine (SAC), seer, skordo, sluon, stinking rose, sudulunu, tafanuwa, ta-suam, ta-suan, tellagada, Tellagaddalu, thiam, thioallyl derivative, thiosulfinates, toi thum, tum, umbi bawang putih, vallaippundu, Velluli, vellulli, verum, vinyl dithiin, vinyldithiin, (Z)-ajoene.
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Multiple studies in humans have reported small reductions in total blood cholesterol and low-density lipoproteins ("bad cholesterol") over short periods of time (4 to 12 weeks). It is not clear if there are benefits after this amount of time. Effects on high-density lipoproteins ("good cholesterol") are not clear. This remains an area of controversy. Well-designed and longer studies are needed in this area.
Anti-fungal (applied to the skin)
Several studies describe the application of garlic to the skin to treat fungal infections, including yeast infections. Take caution as garlic can cause severe burns and rash when applied to the skin of sensitive individuals.
Anti-platelet effects (blood thinning)
The effects of garlic on platelet aggregation have been assessed in several human trials. Because garlic has been associated with several cases of bleeding, therapy should be applied with caution (particularly in patients using other agents that may precipitate bleeding).
Atherosclerosis ("hardening" of the arteries)
Preliminary research in humans suggests that deposits of cholesterol in blood vessels may not grow as quickly in people who take garlic. It is not clear if this is due to the ability of garlic to lower cholesterol levels, or to other effects of garlic.
Preliminary human studies suggest that regular consumption of garlic (particularly unprocessed garlic) may reduce the risk of developing several types of cancer including gastric and colorectal malignancies. Some studies use multi-ingredient products so it is difficult to determine if garlic alone may play a beneficial role. Further well designed human clinical trials are needed to conclude whether eating garlic or taking garlic supplements may prevent or treat cancer.
Preliminary study documented potential benefits of oral plus intravenous garlic in the management of cryptococcal meningitis. Further research is needed before recommending for or against the use of garlic in the treatment of this potentially serious condition, for which other treatments are available.
Familial hypercholesterolemia is a genetic disorder in which very high cholesterol levels run in families. Research in children with an inherited form of high cholesterol suggests that garlic does not have a large effect in lowering cholesterol levels in these patients.
Heart attack prevention in patients with known heart disease
It is not clear if garlic prevents future heart attacks in people who have already had a heart attack. The effects of garlic on cholesterol levels may be beneficial in such patients.
High blood pressure
Numerous human studies report that garlic can lower blood pressure by a small amount, but larger, well-designed studies are needed to confirm this possible effect.
Peripheral vascular disease (blocked arteries in the legs)
Some human studies suggest that garlic may improve circulation in the legs by a small amount, but this issue remains unclear. Better-designed studies are needed.
In early study, self-reports of tick bites were significantly less in people receiving garlic over a placebo "sugar" pill. Further well designed study is needed to confirm these results.
Upper respiratory tract infection
Preliminary reports suggest that garlic may reduce the severity of upper respiratory tract infections. However, this has not been demonstrated in well-designed human studies.
Animal studies suggest that garlic may lower blood sugar and increase the release of insulin, but studies in humans do not confirm this effect.
Stomach ulcers caused by Helicobacter pylori bacteria
Early studies in humans show no effect of garlic on gastric or duodenal ulcers.