This review from 2014 specifically reviewed literature relating to the antihypertensive potential of garlic extracts. Outlining important mechanisms of action including: oxidative stress, nitric oxide bioavailability, hydrogen sulfide production, angiotensin converting enzyme activity, expression of nuclear factor-κB and the proliferation of vascular smooth muscle cells.
Shouk, R., Abdou, A., Shetty, K., Sarkar, D., & Eid, A. H. (2014). Mechanisms underlying the antihypertensive effects of garlic bioactives. Nutrition research (New York, N.Y.), 34(2), 106–115. https://doi.org/10.1016/j.nutres.2013.12.005