Taken from “Potential benefits of garlic and other dietary supplements for the management of hypertension” which was published on Dec 27th 2019 in the Journal of EXPERIMENTAL AND THERAPEUTIC MEDICINE.

Garlic (Allium sativum) has been used globally since ancient times for its diverse effects, and in particular for its cardioprotective properties, including its blood pressure-lowering effects. The findings from different meta-analyses of clinical studies on the anti-hypertensive effects of garlic are inconsistent (42–44); however, the most recently published analysis indicated that garlic supplements are effective for subjects with hypertension and slightly elevated cholesterol levels (45). More than 10 studies performed using Kwai garlic powder have suggested that garlic supplement in doses ranging from 600 to 900 mg/day exert potent effects on blood pressure in hypertensive individuals, but not in normotensive individuals (46). Likewise, in the clinical study by Nakasone et al, treatment with a garlic homogenate-based supplementary diet for 12 weeks resulted in a significant reduction in both SBP and DBP only in patients with hypertension (47). The most consistent effects were observed in studies using aged garlic extract (AGE), another garlic preparation produced through natural aging for >10 months (48). AGE has been shown to significantly reduce blood pressure in patients with uncontrolled hypertension, suggesting that it may be used as a potent adjunct therapy for uncontrolled hypertension (49,50). Intriguingly, Ried et al demonstrated that AGE lowered arterial stiffness, decreased inflammation and improved gut microbiota beneficially for cardiovascular health (51). AGE has also been shown to improve peripheral circulation in hypertensive rats, increase the plasma level of NO in mice and induce endothelium-dependent vasorelaxation of isolated rat aortic rings (52–54).

Allicin has been considered as a major active ingredient in garlic supplementation, since it has been reported to exert angiotensin II-inhibiting and vasodilating effects (55,56). In addition to allicin, γ-glutamyl-S-allylcysteine (GSAC) may contribute to the effects by inhibiting ACE and inducing endothelium-dependent and -independent relaxation (47). In AGE, allicin and GSAC are chemically converted to other sulfur compounds including S-allylcysteine (SAC) and S−1-propenylcysteine (S1PC) during the aging process. SAC has been shown to reduce renal injury and hypertension in 5/6 nephrectomized rats, which was shown to be associated with its antioxidant properties (57). Both the single and repeated administration of S1PC have been shown to significantly lower blood pressure in hypertensive rats by modulating various regulatory molecules, such as histidine, tryptophan and lyso-phosphatidylcholine (58,59). The anti-hypertensive mechanisms of AGE appear to be divergent due to its various active ingredients.

The majority of studies have stated that garlic supplements are very safe. Only a few studies have reported that the use of garlic may cause adverse events, such as malodorous breath, body odor and mild gastrointestinal disturbances (60,61). These side-effects are prominently observed in studies using raw garlic and are alleviated in interventions with AGE (62).