Garlic
Summary
Garlic supplements lowered blood pressure in a meta-analysis of 20 trials, most in people with high readings. Cholesterol results conflict: one review of 13 trials found no change. A Cochrane review found a single cold trial. NCCIH notes garlic may raise bleeding risk, which matters around surgery and with blood thinners.
Key facts
- About 5/2.5 mm Hg lower than placebo across 20 trials, and 8.7/6.1 mm Hg in people with hypertension[2]
- A 13-trial review found no change in total or LDL cholesterol; an earlier pooled analysis reported about 10% lower in people with raised levels[3][2]
- Only one adequate trial (146 people); Cochrane called the evidence insufficient[4]
- Used in research for up to 7 years; breath and body odour, stomach upset; may raise bleeding risk[1]
- 3 graded human outcomes on this page
- October 11, 2026
How it works
ProposedCrushing garlic converts alliin to allicin and other sulfur compounds; aged extracts are rich in S-allyl cysteine. Proposed blood-pressure effects involve nitric oxide and hydrogen sulfide signalling, mainly from laboratory data.[2]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Blood pressure | Grade B | Improved | Meta-analysis of 20 trials · n = 970 · 2016 | 1 row |
| Colds | Grade D | Improved | Systematic review · n = 146 · 2014 | 1 row |
| Cholesterol | No effect | No effect | Meta-analysis of 13 trials · n = 1,056 · 2009 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Blood pressure | Improved | Grade B | Meta-analysis · n = 970 · 2016 Adults in 20 placebo-controlled trials; subgroup with hypertension Form: Garlic preparations (powder, aged extract) · Dose: Varied across trials · Duration: Varied across trials Systolic pressure fell 5.1 mm Hg and diastolic 2.5 mm Hg versus placebo; in people with hypertension, 8.7 and 6.1 mm Hg. | 26764326 (opens PubMed)Source [2] |
| Common colds | Improved | Grade D | Systematic review · n = 146 · 2014 Adults in the single trial meeting Cochrane criteria Form: Garlic supplement with 180 mg allicin · Dose: Once daily · Duration: 12 weeks 24 colds with garlic versus 65 with placebo, with fewer days ill; recovery time was similar. One trial only, so evidence was judged insufficient. | 25386977 (opens PubMed)Source [4] |
| Total and LDL cholesterol | No effect | No effect | Meta-analysis · n = 1,056 · 2009 Healthy and hypercholesterolaemic adults in 13 trials Form: Garlic preparations · Dose: Varied across trials · Duration: 11–24 weeks No significant change in total cholesterol, LDL, HDL, triglycerides or apolipoprotein B versus placebo; heterogeneity was moderate to high. | 19250134 (opens PubMed)Source [3] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Dried garlic powder (allicin-releasing) | Varies | No head-to-head human absorption data in the sources cited here. | Breath and body odour and stomach upset are the usual complaints.[1] | Most blood-pressure and cholesterol trials |
| Aged garlic extract (S-allyl cysteine) | Varies | No head-to-head human absorption data in the sources cited here. | Usually less odour; no separate tolerance data in the sources cited here. | Several blood-pressure trials |
Studied doses
Doses studied in human trials ranged from garlic powder and aged-extract products to allicin-standardised capsules, with no single dose across the reviews cited here; the cold trial used a capsule with 180 mg allicin daily for 12 weeks.[2][3][4]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- Anticoagulants and antiplatelet drugsNIH fact sheetNCCIH says garlic supplements may increase bleeding risk and advises telling your provider, especially before surgery or with medicines that affect bleeding.[1]
- Diabetes medicinesNIH fact sheetNCCIH notes garlic supplements may lower blood sugar slightly in people with diabetes.[1]
Who should be careful
- Before surgery or on blood thinners
- Possible added bleeding risk.[1]
- Pregnancy and breastfeeding
- NCCIH says garlic may not be safe in pregnancy or breastfeeding in amounts above those in food.[1]
- Garlic allergy
- Some people have allergic reactions to garlic.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Frequently asked questions
Does garlic lower blood pressure?
Pooled trials found about 5/2.5 mm Hg lower readings than placebo, larger in people with hypertension.[2]
Does garlic lower cholesterol?
Results conflict: a 13-trial review found no change, while an earlier analysis reported about 10% lower levels in people with raised cholesterol.[3][2]
Is aged garlic extract different from garlic powder?
Yes: aged extract is rich in S-allyl cysteine and causes less odour; trials used both, and the reviews here pool them.[2]
Is garlic safe with blood thinners?
NCCIH says garlic supplements may increase bleeding risk; tell your clinician, especially before surgery.[1]
Sources
- [1]Garlic. National Center for Complementary and Integrative Health (NCCIH), 2025. fact-sheet
- [2]Garlic Lowers Blood Pressure in Hypertensive Individuals, Regulates Serum Cholesterol, and Stimulates Immunity: An Updated Meta-analysis and Review.. J Nutr, 2016. meta-analysis
- [3]Garlic supplementation and serum cholesterol: a meta-analysis.. J Clin Pharm Ther, 2009. meta-analysis
- [4]Garlic for the common cold.. Cochrane Database Syst Rev, 2014. systematic-review
What changed
- First draft. Every PMID checked against NCBI E-utilities (title, journal and year taken from the PubMed record) and each evidence row written from its PubMed abstract; self-reviewed in a separate adversarial pass.