By: Fernando Gonzalez, CSUN Dietetic Intern Cohort 2021-2023

High blood pressure, also known as hypertension, is a common condition in which the force of blood pushing against the artery wall is too high.¹ Though it often presents no symptoms, high blood pressure may lead to heart disease, the leading cause of death in the United States.² Many individuals currently treat their high blood pressure with prescribed medication, however, many are left dissatisfied as the medication is often riddled with discomforting side effects such as headaches and nausea.³ Due to these side effects, a wave of people have grown interest in finding a “natural way” to treat their hypertension, such as using garlic. Let’s discuss the therapeutic properties of garlic, what research tells us, and what the contraindications might be before deciding to treat high blood pressure with garlic.  

What Makes Garlic Potent? 

Garlic (scientifically named Allium Sativum) is a culinary and medicinal herb that has been used throughout history. Garlic not only contains a range of vitamins and minerals, but also has bioactive compounds that can be used for medicinal purposes.⁴ Allicin, the main active compound that gives garlic its distinct pungency and flavor, is thought to be responsible for garlic’s effect on blood pressure, along with allicin’s sulfur-containing products when garlic is crushed or aged.^5,6  

Garlic can be processed and prepared in many ways for culinary use and to be incorporated into supplements. Peeled, crushed, and dehydrated cloves are ground to a fine powder and packed or prepared in tablet form for supplementing.⁷ Additionally, aging garlic is also a popular method found in many supplements and is produced by chopping garlic and placing it in an alcohol solution for several months.⁸ It has been observed that aging garlic can produce additional sulfur-containing compounds that also provide many health properties such as improved immunity and anti-inflammation.⁵ 

So how does garlic help hypertension? Well, garlic’s bioactive compounds appear to have an influence on controlling blood pressure. Growing evidence has suggested that allicin-derived products convert into hydrogen sulfide.⁹ Hydrogen sulfide is known to have a function in cell signaling for vasodilation, the term for when blood vessels in your body widen, lowering your blood pressure.⁹ Additionally, garlic’s allicin compound may prevent the production of angiotensin II, a hormone that causes the walls of the arteries to constrict, increasing blood pressure.^10,11 

Evidence in Research 

So what research is available to prove these effects? In 2016, Ried et al. conducted a placebo-controlled trial to assess the outcome of aged garlic extract on blood pressure and other cardiovascular risk factors in uncontrolled hypertensives.¹² For 12 weeks, 50 participants were given a daily intake of 1.2 g of aged-garlic extract capsules, while 38 participants were assigned a placebo. The results of the study revealed a significant reduction in the experimental group’s systolic blood pressure when compared to the control group after 12 weeks, with a mean reduction from 148.7 mmHg to 141.7 mmHg. Overall, the findings imply that aged garlic extract can help patients with hypertension reduce their blood pressure.  

In another similar trial, Sobenin et al. conducted a placebo-controlled trial with the aim to observed the hypotensive effects of a time-released garlic powder tablets (Allicor) against a placebo.¹³ 84 participants with mild or moderate hypertension were randomly assigned either 600mg of Allicor or a placebo daily for 8 weeks. The Allicor supplementation resulted in a significant reduction of systolic pressure by 7.0mmHg and diastolic pressure by 3.8mmHg. The results of this study show that the time-released garlic powder is an effective treatment for mild and moderate hypertension.  

Contraindications of Garlic Supplementation 

The majority of investigations on garlic supplements have concluded that high doses are generally safe. However, a few studies have found that garlic supplementation may cause negative effects such as poor breath, body odor, and moderate gastrointestinal upset.¹⁴ More research on the safety and toxicity of garlic, as well as its interaction with other enzymes and transporters, is needed. 

Patients should speak with their physician if they plan on taking garlic with any blood thinners such as anticoagulants or antiplatelet drugs. The consumption of garlic may increase the risk of bleeding when paired with blood thinners such as warfarin and aspirin.¹⁵ Garlic supplementation may have anticoagulant properties that when paired with blood thinners, can lead to cases of hematuria and increased international normalized ratio, which indicates a high risk of bleeding.¹⁶ Moreover, individuals should avoid taking garlic with other herbal supplements that are known to affect blood clotting such as ginger, cranberry, and dong quai, as it may amplify the herbs’ effect and cause bleeding.¹⁷ Patients awaiting surgery should not be taking garlic supplements, as blood thinners are commonly used prior to surgery to prevent blood clots and may lead to excessive bleeding during or after surgery.¹⁶ Garlic should therefore be avoided seven to ten days before surgery to mitigate any unwanted drug-nutrient interactions.¹⁸ 

According to research, garlic consumption has the ability to help regulate blood pressure.^12,13 Patients and health providers must be aware that garlic consumption and garlic supplements interfere with some medications. These nutrient-drug combinations can have major health consequences. Of course, the extent to which nutrient-drug interactions occur will be influenced by dosages, the period between supplements and medication administration, and hereditary factors. Before recommending garlic for hypertension, a health professional should weigh the advantages with the hazards.  

Individuals that need help controlling hypertension through diet and lifestyle can seek guidance from a dietitian. If interested, consider the Marilyn Magaram Center for nutrition guidance and counseling through the following link: https://www.csun.edu/marilyn-magaram-center/products-services.

References

1. Mayo Clinic Staff. High blood pressure (hypertension). Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/high-blood-pressure/symptoms-causes/syc-20373410. Published September 15, 2022. Accessed December 4, 2022.  
2. CDC/National Center for Health Statistics. FASTSTATS – leading causes of death. Centers for Disease Control and Prevention. https://www.cdc.gov/nchs/fastats/leading-causes-of-death.htm. Published September 6, 2022. Accessed December 4, 2022.  
3. AHFS Patient Medication Information. Lisinopril: Medlineplus Drug Information. MedlinePlus. https://medlineplus.gov/druginfo/meds/a692051.html. Accessed December 4, 2022.  
4. Szychowski K, Rybczyńska-Tkaczyk K, Gaweł-Bęben K, et al. Characterization of active compounds of different garlic (allium sativum L.) cultivars. Polish Journal of Food and Nutrition Sciences. 2018;68(1):73-81. doi:10.1515/pjfns-2017-0005  
5. Matsutomo T. Potential benefits of garlic and other dietary supplements for the management of hypertension (review). Experimental and Therapeutic Medicine. 2019. doi:10.3892/etm.2019.8375  
6. Macpherson LJ, Geierstanger BH, Viswanath V, et al. The pungency of garlic: Activation of TRPA1 and TRPV1 in response to allicin. Current Biology. 2005;15(10):929-934. doi:10.1016/j.cub.2005.04.018  
7. Li Y, Xu S-Y, Sun D-W. Preparation of garlic powder with high allicin content by using combined microwave–vacuum and vacuum drying as well as microencapsulation. Journal of Food Engineering. 2007;83(1):76-83. doi:10.1016/j.jfoodeng.2007.02.057  
8. Charron CS, Milner JA, Novotny JA. Garlic. Encyclopedia of Food and Health. 2016:184-190. doi:10.1016/b978-0-12-384947-2.00346-9  
9. Benavides GA, Squadrito GL, Mills RW, et al. Hydrogen sulfide mediates the vasoactivity of garlic. Proceedings of the National Academy of Sciences. 2007;104(46):17977-17982. doi:10.1073/pnas.0705710104  
10. Ried K, Fakler P. Potential of garlic (allium sativum) in lowering high blood pressure: Mechanisms of action and clinical relevance. Integrated Blood Pressure Control. 2014:71. doi:10.2147/ibpc.s51434  
11. Cleveland Clinic medical professional. Angiotensin: What it is, causes & function. Cleveland Clinic. https://my.clevelandclinic.org/health/articles/23359-angiotensin. Accessed December 4, 2022.  
12. Ried K, Travica N, Sali A. The effect of aged garlic extract on blood pressure and other cardiovascular risk factors in uncontrolled hypertensives: The age at heart trial. Integrated Blood Pressure Control. 2016:9. doi:10.2147/ibpc.s93335  
13. Sobenin IA, Andrianova IV, Fomchenkov IV, Gorchakova TV, Orekhov AN. Time-released garlic powder tablets lower systolic and diastolic blood pressure in men with mild and moderate arterial hypertension. Hypertension Research. 2009;32(6):433-437. doi:10.1038/hr.2009.36  
14. Ackermann RT, Mulrow CD, Ramirez G, Gardner CD, Morbidoni L, Lawrence VA. Garlic shows promise for improving some cardiovascular risk factors. Archives of Internal Medicine. 2001;161(6):813. doi:10.1001/archinte.161.6.813  
15. National Center for Complementary and Integrative Health. Garlic. National Center for Complementary and Integrative Health. https://www.nccih.nih.gov/health/garlic. Published 2020. Accessed December 4, 2022.  
16. Ge B, Zhang Z, Zuo Z. Updates on the clinical evidenced herb-warfarin interactions. Evidence-Based Complementary and Alternative Medicine. 2014;2014:1-18. doi:10.1155/2014/957362  
17. Abebe W. Review of herbal medications with the potential to cause bleeding: Dental implications, and risk prediction and prevention avenues. EPMA Journal. 2019;10(1):51-64. doi:10.1007/s13167-018-0158-2  
18. Burnham BE. Garlic as a possible risk for postoperative bleeding. Plastic and Reconstructive Surgery. 1995;95(1):213. doi:10.1097/00006534-199501000-00060