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HERBS: Garlic


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Garlic

Garlic

Scientific name

Allium sativum

Other names

Nectar of the gods, camphor of the poor, da-suan, la-suan, stinking rose

Brand name

Garlique®, Kwai®, Kyolic®, One-a-day Garlic

Purported uses

  • To fight infections of the skin: Laboratory studies show that raw garlic has antibacterial, antiviral, antiparasitic, and antifungal activity. There is no proof from clinical trials that this effect occurs in the human body.
  • To prevent and treat cancer: A few clinical trials suggest that high garlic consumption may lower the risk of stomach and colorectal cancers. No evidence supports the use of garlic as a cancer treatment. 
  • To treat heart disease: Several clinical trials show that use of garlic supplements reduces cholesterol and triglyceride levels in the blood, which may reduce the risk of heart disease, but a handful of clinical trials contradict these findings. Clinical trials studying the effect of garlic on blood pressure and risk of heart disease have shown mixed results. 
  • As an antioxidant: No scientific evidence supports this use.
  • To treat atherosclerosis: Several clinical trials show that use of garlic supplements reduces blood pressure as well as cholesterol and triglyceride blood levels, which are risk factors for developing atherosclerosis, but a handful of clinical trials contradict these findings. Clinical and laboratory studies support garlic’s antiplatelet activity, which may help prevent blood clots in patients with atheroclerosis. 
  • To lower high cholesterol: Several clinical trials show that use of garlic supplements reduces cholesterol and triglyceride levels in the blood, but a handful of clinical trials contradict these findings. 
  • To lower high blood pressure: Clinical trials studying the effects of garlic on blood pressure have shown mixed results.
  • To treat circulatory disorders: Clinical and laboratory studies support garlic’s antiplatelet activity, which may help prevent blood clots in patients with circulatory disorders. Otherwise no scientific evidence supports this use.

Warnings

Discontinue use of garlic at least 7 days prior to surgery.

Adverse reactions

  • Reported (Oral): Headache, fatigue, altered platelet function with potential for bleeding, offensive odor, GI upset, diarrhea, sweating, changes in the intestinal flora, hypoglycemia.
  • Case Report (Oral): Prolonged bleeding time with spinal epidural hematoma and platelet dysfunction has occurred following excessive usage of garlic.
  • Reported (Topical): Contact dermatitis.

Drug interactions

  • Insulin: Dose of insulin may require adjustment due to hypoglycemia effects of garlic.
  • Warfarin: Anticoagulant activity may be enhanced due to increased fibrinolytic activity and diminished human platelet aggregation.
  • Cytochrome P450 3A4: Garlic may cause induction of the 3A4 isoenzyme resulting in enhanced metabolism of certain drugs.
  • Cyclosporine: Effectiveness might be decreased by garlic’s ability to induce metabolism and decrease levels of drugs like cyclosporine which are substrates of cytochrome P450 3A4. It can potentially cause transplant rejection.
  • Saquinavir (Fortovase, Invirase): Consuming garlic can significantly decrease serum concentration levels. Garlic can decrease peak levels by 54% and mean trough levels by 49%. These reductions in levels can cause therapeutic failure and increase development. It is suspected that garlic induces cytochrome P450 metabolism of saquinavir. Patients taking other protease inhibitors may be affected; however, only saquinavir interaction has been reported.

References

1. Newall CA, et al. Herbal Medicines: A Guide for Health Care Professionals. London: Pharmaceutical Press; 1996.

2. Amagase H, et al. Intake of garlic and its bioactive components. J Nutr 2001;131:955S-62S.

3. Tyler, V. Herbs of Choice, the Therapeutical Use of Phytomedicinals. Binghamton: Pharmaceutical Press; 1994.

4. Qureshi AA, et al. Suppression of avian hepatic lipid metabolism by solvent extracts of garlic: impact on serum lipids. J Nutr 1983;113:1746-55.

5. Pedraza-Chaverri J, et al. Garlic prevents hypertension induced by chronic inhibition of nitric oxide synthesis. Life Sci 1998;62:71-7.

6. Dirsch VM, et al. Effect of allicin and ajoene, two compounds of garlic, on inducible nitric oxide synthase. Atherosclerosis 1998;139:333-9.

7. Sato T, Miyata G. The nutraceutical benefit, part iv: garlic. Nutrition 2000;16:787-8.

8. Song K, Milner JA. The influence of heating on the anticancer properties of garlic. J Nutrition 2001;131:1054S-7S.

9. Blumenthal M. Herbal Medicine, Expanded Commission E Monographs, 1st ed. Austin: American Botanical Council; 2000.

10. Rose KD, et al. Spontaneous spina epidural hematoma with associated platelet dysfunction from excessive garlic ingestion: a case report. Neurosurgery 1990;26:880-2.

11. Brinker F. Herb Contraindications and Drug Interactions, 2nd ed. Sandy (OR): Eclectic Med Publications; 1998.

12. Piscitelli SC, et al. The effect of garlic supplements on the pharmacokinetics of saquinavir. Clin Infect.Dis. 2002;34:234-8.

13. Hodge G, et al. Allium sativum (garlic) suppresses leukocyte inflammatory cytokine production in vitro: potential therapeutic use in the treatment of inflammatory bowel disease. Cytometry 2002;48:209-15.

14. Hirsch K, et al. Effect of purified allicin, the major ingredient in freshly crushed garlic, on cancer cell proliferation. Nutr Cancer 2000;38:245-54.

15. Ang-lee M, et al. Herbal Medicines and perioperative care. JAMA 2001;286:208-16.

16. Kannar D, et al. Hypocholesterolemic effect of an enteric coated garlic supplement. J Am Coll Nutr 2001;20:225-31.

17. Ackermann RT, et al. Garlic shows promise for improving some cardiovascular risk factors. Arch Intern Med 2001;161:813-24.

18. Stevinson C, et al. Garlic for treating hypercholesterolemia: a meta-analysis of randomized clinical trials. Ann Intern Med 2000;133:420-9.

19. Fleischauer AT, et al. Garlic consumption and cancer prevention: meta-analyses of colorectal and stomach cancers. Am J Clin Nutr 2000;72:1047-52.

20. Ankri S, et al. Antimicrobial properties of allicin from garlic. Microbes Infect 1999;1:125-9.

21. Isaacsohn JL, et al. Garlic powder and plasma lipids and lipoproteins: a multicenter, randomized, placebo-controlled trial. Arch Inter Med 1998;158:1189-94.

22. Berthold HK, et al. Effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism: a randomized controlled trial. JAMA 1998;279:1900-2.

23. Silagy CA, et al. A meta-analysis of the effect of garlic on blood pressure. J Hypertension 1994;12:463-8.

24. Jain AK, et al. Can garlic reduce levels of serum lipids? A controlled clinical study. Am J Med 1993;94:632-5.

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Overview of Herbs | Alfalfa | Aloe Vera | Burdock | Capsaicin | Cascara | Chamomile | Chaparral | Comfrey | Echinacea | Garlic | Ginger | Ginseng (Asian) | Ginseng (American) | Gotu Kola | Hawthorn | Licorice | Ephedra | Milk Thistle | Sassafras | Blue-Green Algae