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Garlic

Pooled trials in people with high blood pressure report systolic drops of about 7 to 8 mmHg. Total cholesterol fell 10 to 17 mg/dL in two large pooled analyses, and fasting glucose and HbA1c fell modestly. One trial reported fewer colds. Garlic halved saquinavir levels in one study. Platelet trials were mixed, and odor and rash are reported.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplement and food in the US. Not approved as a drug for any use.
Also called
Allium sativum, aged garlic extract, AGE, Kyolic, allicin, garlic powder, garlic oil, black garlic
Taken for
blood pressure, cholesterol, blood sugar, inflammation, common cold, immunity, heart health, blood thinning

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help5

Reported risks3

What people take it for, and what was found

Shown to help5

Strong

Blood pressure in people with hypertension

Shown to lower blood pressure about 7 to 8 mmHg systolic and 5 mmHg diastolic in adults with hypertension.

The numbers and sources
Effect
In 12 trials (553 hypertensive participants), garlic lowered systolic pressure by a mean 8.3 ± 1.9 mmHg, and in 8 trials (374 participants) diastolic pressure by 5.5 ± 1.9 mmHg [1]. A second meta-analysis of 7 placebo-controlled trials found systolic pressure fell 6.71 mmHg (95% CI -12.44 to -0.99) and diastolic 4.79 mmHg (95% CI -6.60 to -2.99), with no serious adverse events reported [2].
Population
Adults with hypertension [1][2].
Sources
[1], [2]
Caveats
Trials are small. Review [1] has one author and summarizes trials of Kyolic aged garlic extract. Its abstract does not report funding. The authors of [2] call for longer trials focused on primary endpoints.
Strong

Cholesterol

Shown to lower total cholesterol about 10 to 17 mg/dL and LDL about 6 to 9 mg/dL in adults, more in those with high cholesterol.

The numbers and sources
Effect
Across 39 trials, garlic lowered total cholesterol by 17 ± 6 mg/dL and LDL by 9 ± 6 mg/dL in people with total cholesterol above 200 mg/dL, when taken for longer than 2 months. HDL rose slightly and triglycerides did not change significantly [3]. A 2026 meta-analysis of 108 trials (7,137 adults) found total cholesterol fell 10.21 mg/dL (95% CI -13.69 to -6.74), LDL 5.90 mg/dL, and triglycerides 5.82 mg/dL, while HDL rose 2.18 mg/dL [4].
Population
Adults in 39 trials, effects reported in those with elevated cholesterol [3]. Adults in 108 trials [4].
Sources
[3], [4]
Caveats
The abstract of [3] describes earlier meta-analyses on this question as conflicting. The authors of [4] report larger effects in adults with unfavorable baseline risk factors and call for larger, longer, more rigorous trials. The two reviews disagree on triglycerides.
Moderate

Blood sugar

Shown to lower fasting glucose, and HbA1c by about 0.5 points, more in people with type 2 diabetes. Insulin did not change.

The numbers and sources
Effect
In 9 RCTs (768 patients with type 2 diabetes), fasting glucose was lower with garlic at 1 to 2, 3 to 4, 12 and 24 weeks. Fructosamine and HbA1c were lower at 12 and 24 weeks. Complications did not differ [5]. A 2026 GRADE-assessed meta-analysis of 27 RCTs (1,619 adults) found fasting glucose fell 2.76 mg/dL (95% CI -5.11 to -0.41) and HbA1c 0.53 percentage points (95% CI -0.86 to -0.20). Insulin and HOMA-IR did not change significantly [6]. In 8 trials in type 2 diabetes, fasting glucose fell 12.41 mg/dL and HbA1c 0.5 points [7]. The 108-trial review found fasting glucose 2.77 mg/dL lower [4].
Population
Adults with type 2 diabetes [5][7]. Adults in 27 RCTs [6] and 108 trials [4].
Sources
[4], [5], [6], [7]
Caveats
The reviews pooled different populations, and the fasting glucose drop in the type 2 diabetes review [7] is more than four times that in the all-adult reviews. The pooled standardized differences in [5] are very large (SMD -21.02 at 24 weeks), which points to small, varied trials. Heterogeneity in [7] was very high (I² 99.2% for fasting glucose), and its authors rate the included trials as low quality.
Moderate

Inflammation markers

Shown to lower CRP by about 0.6 mg/L and lower TNF in adults. These are blood markers, and the reviews disagree on IL-6.

The numbers and sources
Effect
In 16 RCTs, garlic lowered CRP by 0.61 mg/L (95% CI -1.12 to -0.11, I² 76.9%, 13 trials), IL-6 by 0.73 ng/L (5 trials) and TNF by 0.26 ng/L (7 trials). Adiponectin and leptin did not change significantly [8].
Population
Adults in 16 RCTs lasting 2 to 52 weeks [8].
Sources
[4], [8]
Caveats
Blood markers, not clinical outcomes. Heterogeneity for CRP was high [8]. The 108-trial review found CRP 1.6 mg/L and TNF 3.94 pg/mL lower, effects several times larger than [8], and found no change in IL-6 [4].
Limited

Common cold

One trial found 24 colds on garlic against 65 on placebo over 12 weeks. Days to recovery were similar.

The numbers and sources
Effect
A Cochrane review found only one eligible trial. Its 146 participants on a daily garlic supplement for 12 weeks reported 24 colds against 65 on placebo, and 111 against 366 days of illness. Days to recovery were similar, 4.63 against 5.63 [9].
Population
146 adults in one trial [9].
Sources
[9]
Caveats
One trial with self-reported colds. The review authors found the evidence insufficient [9].

Doses studied

The cold trial gave a supplement with 180 mg of allicin once a day for 12 weeks [9]. The diabetes trials used 0.05 to 1.5 g a day [5], and the inflammation trials 12 to 3,600 mg a day [8]. Cholesterol effects were reported with use beyond 2 months [3].

Risks

Reported risks2

LimitedHow often is not known

Lower levels of the HIV drug saquinavir

One small study found garlic cut blood levels of the HIV drug saquinavir by about half in healthy adults.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In 10 healthy volunteers, 3 weeks of garlic caplets cut saquinavir exposure (AUC) by 51%, trough levels by 49% and peak levels by 54%. After a 10-day washout, levels were back to only 60% to 70% of baseline [10].
Population
10 healthy adults [10].
Sources
[10]
Caveats
One small pharmacokinetic study of one drug.
ModerateHow often is not known

Odor, allergy and skin burns

Garlic breath and body odor were the most common complaints in trials. Case reports describe allergic reactions and skin burns from fresh garlic.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Garlic breath and body odor are the most common complaints in trials. Case reports describe allergic reactions including contact dermatitis, urticaria and anaphylaxis, and burns where fresh garlic was applied to skin under dressings [11]. The cold trial reported rash and odor [9].
Population
Trial participants and case reports [9][11].
Sources
[9], [11]
Caveats
Case reports cannot give a rate.

Mixed results1

LimitedHow often is not known

Platelets, bleeding and warfarin

Limited evidence: case reports describe bleeding risk and stronger warfarin effects, while small trials found no added bleeding or INR change with warfarin.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
A review of case reports describes altered platelet function and coagulation with a possible bleeding risk, and enhanced effects of warfarin and fluindione [11]. In 48 patients on warfarin, 5 mL of aged garlic extract twice a day for 12 weeks showed no increase in bleeding against placebo [12]. In a systematic review of 12 RCTs (595 participants), 6 found less platelet aggregation, and the authors could not reach a conclusion [13]. In 12 healthy men, garlic did not alter warfarin levels or INR [14].
Population
Case reports [11], 48 warfarin patients [12], 12 RCTs [13], 12 healthy men [14].
Sources
[11], [12], [13], [14]
Caveats
Case reports and controlled trials point in different directions. The trials were small and short.

Claims tested and not found

  1. That garlic shortens a cold once it starts. In the one eligible trial, days to recovery were 4.63 on garlic and 5.63 on placebo, a difference the review described as similar [9].

Sources

  1. Ried K. Garlic lowers blood pressure in hypertensive subjects, improves arterial stiffness and gut microbiota: A review and meta-analysis. Experimental and Therapeutic Medicine. 2019. https://doi.org/10.3892/etm.2019.8374
  2. Xiong X, Wang P, Li S, et al. Garlic for hypertension: A systematic review and meta-analysis of randomized controlled trials. Phytomedicine. 2015. https://doi.org/10.1016/j.phymed.2014.12.013
  3. Ried K, Toben C, Fakler P. Effect of garlic on serum lipids: an updated meta-analysis. Nutrition Reviews. 2013. https://doi.org/10.1111/nure.12012
  4. Behrouz V, Zahroodi M, Clark CCT, et al. Effects of Garlic Supplementation on Cardiovascular Risk Factors in Adults: A Comprehensive Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrition Reviews. 2026. https://doi.org/10.1093/nutrit/nuaf090
  5. Wang J, Zhang X, Lan H, et al. Effect of garlic supplement in the management of type 2 diabetes mellitus (T2DM): a meta-analysis of randomized controlled trials. Food & Nutrition Research. 2017. https://doi.org/10.1080/16546628.2017.1377571
  6. Alsanie SA, Alblaji M, Almutairi SM, et al. Effects of garlic supplementation on glycemic indices in adults: a GRADE-assessed systematic review and dose-response meta-analysis of randomized controlled trials. Diabetes Research and Clinical Practice. 2026. https://doi.org/10.1016/j.diabres.2026.113407
  7. Ebrahimzadeh A, Safargar M, Rajabzadeh-Dehkordi M, et al. The Therapeutic Effect of Garlic Supplements on the Metabolic Profile of Patients With Type 2 Diabetes: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Nutrition and Metabolic Insights. 2026. https://doi.org/10.1177/11786388251413660
  8. Darooghegi Mofrad M, Milajerdi A, Koohdani F, et al. Garlic Supplementation Reduces Circulating C-reactive Protein, Tumor Necrosis Factor, and Interleukin-6 in Adults: A Systematic Review and Meta-analysis of Randomized Controlled Trials. The Journal of Nutrition. 2019. https://doi.org/10.1093/jn/nxy310
  9. Lissiman E, Bhasale AL, Cohen M. Garlic for the common cold. Cochrane Database of Systematic Reviews. 2014. https://doi.org/10.1002/14651858.CD006206.pub4
  10. Piscitelli SC, Burstein AH, Welden N, et al. The Effect of Garlic Supplements on the Pharmacokinetics of Saquinavir. Clinical Infectious Diseases. 2002. https://doi.org/10.1086/324351
  11. Borrelli F, Capasso R, Izzo AA. Garlic (Allium sativum L.): Adverse effects and drug interactions in humans. Molecular Nutrition & Food Research. 2007. https://doi.org/10.1002/mnfr.200700072
  12. Macan H, Uykimpang R, Alconcel M, et al. Aged Garlic Extract May Be Safe for Patients on Warfarin Therapy. The Journal of Nutrition. 2006. https://doi.org/10.1093/jn/136.3.793S
  13. Mollahosseini M, Hosseini-Marnani E, Panjeshahin A, et al. A systematic review of randomized controlled trials related to the effects of garlic supplementation on platelet aggregation. Phytotherapy Research. 2022. https://doi.org/10.1002/ptr.7556
  14. Mohammed Abdul MI, Jiang X, Williams KM, et al. Pharmacodynamic interaction of warfarin with cranberry but not with garlic in healthy subjects. British Journal of Pharmacology. 2008. https://doi.org/10.1038/bjp.2008.210

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