Garlic (Allium sativum) is a vegetable that can be eaten raw or cooked. It is also sold as a dietary supplement. Garlic contains several sulfur-containing phytochemicals that are metabolized when eaten and can affect cardiovascular health and inflammation.^[1] These chemicals include allicin, diallyl disulfide (DADS), diallyl trisulfide (DATS), and S-allylmercaptocysteine (SAMC).

Supplementation with garlic lowers circulating markers of oxidative stress^[2][3] (e.g., malondialdehyde) and inflammation (e.g., C-reactive protein and TNF-α).^[4][5][6] Supplementation with garlic can also reduce total cholesterol levels,^[7][8] particularly in people with cardiovascular disease, and improve other measures of cardiovascular health (coronary artery calcium, carotid intima-media thickness, etc.).^[9] However, its direct effects on cardiovascular morbidity and mortality are currently unclear.^[9][10]

Observational studies also show that garlic consumption, through food or as a supplement, is associated with a lower risk of gastric and colorectal cancers.^[11]

Garlic consumption can cause “garlic breath” and body odor, which are typically most pronounced after eating raw garlic.^[12] These side effects are also frequent-reported “adverse events” in clinical trials.^[12][13][14] Some supplement formulations (e.g., aged garlic extract) are designed to minimize such odors.^[15][16]

In rare cases, garlic may cause an allergic reaction.^[12]

Metabolizing garlic’s sulfur-containing chemicals (i.e., allicin, diallyl disulfide, diallyl trisulfide, and S-allylmercaptocysteine) eventually produces hydrogen sulfide (H₂S). H₂S is not only responsible for the characteristic garlic odor, but is also a signaling molecule with direct effects on vascular tissue, nerve synapses, inflammatory processes, and more.^[17] However, the sulfur-containing chemicals in garlic also have their own direct effects, activating several signaling pathways involved in anti-oxidant, anti-thrombotic, and anti-inflammatory mechanisms,^[18][19] which explains garlic's role in cardiovascular health.^[9] These chemicals also likely regulate the cell cycle in cancer cells, causing apoptosis (cell death),^[11][20] which explains the potential role of garlic in lowering gastric and colorectal cancer risk.^[11]