Garlic supplements lower blood pressure by an average of 5 to 9 mmHg and LDL cholesterol by approximately 10% in people with already elevated levels, provided they are used for longer than 2 months. The effect is real but modest, and garlic does not replace regular medication.
Several meta-analyses of randomised trials show that garlic supplements can moderately lower blood pressure. In people who already have elevated blood pressure (above 140/90 mmHg), the average reduction is approximately 8.7 mmHg systolic (upper reading) and 6.1 mmHg diastolic (lower reading). Across all participants combined, the average effect is somewhat smaller: approximately 5.1 mmHg systolic and 2.5 mmHg diastolic. This was measured across 20 randomised trials involving 970 participants (PMID 26764326, 39437887, 39275211). A reduction of 5-9 mmHg is modest but not negligible, and is comparable to the effect of lifestyle measures such as exercising more or eating less salt.
Aged garlic extract (AGE) shows a similar pattern in a separate meta-analysis of 9 studies (584 participants): an average of 4 mmHg lower systolic and nearly 1.5 mmHg lower diastolic. An important detail: a significant effect on diastolic pressure was only seen at doses above 1200 mg per day. Lower doses had little or no measurable effect on diastolic pressure (PMID 39437887). One small study also examined a low-dose black garlic extract as an addition to existing blood pressure medication and found a small additional reduction of 1.8 mmHg systolic. However, that study was partly funded by the manufacturer, which limits its reliability (PMID 37686723).
For cholesterol, the picture is more positive than was previously assumed. A meta-analysis of 39 randomised trials with 2300 participants showed that garlic supplements can lower total and LDL cholesterol (the 'bad' cholesterol) by approximately 10%, but only in people with mildly elevated cholesterol (above 200 mg/dL) and only with use lasting longer than 2 months (PMID 26764326). A broader systematic review also confirms beneficial effects on triglycerides, HDL cholesterol ('good' cholesterol), and inflammatory markers in the blood (PMID 35193446). A smaller double-blind study using a combined garlic-onion extract also found significant reductions in LDL and total cholesterol after 8 weeks (PMID 39203947).
Older literature (2002) concluded that the cholesterol-lowering effect of garlic was too small to recommend clinically (PMID 12391714). More recent and larger meta-analyses paint a slightly more positive picture, but the question of how clinically meaningful a 10% reduction actually is remains relevant. The active compound allicin has clearly demonstrated mechanisms in laboratory research that can lower blood pressure and cholesterol through chemical processes in cells (PMID 25153873), but laboratory results are not automatically transferable to humans.
A crucial safety point: garlic must not replace regular blood pressure or cholesterol medication. No long-term studies exist demonstrating that garlic actually prevents heart attacks, strokes, or death. The available studies measure intermediate variables (blood pressure, cholesterol), not hard clinical endpoints. Use as a supplement alongside medication is something to discuss with a doctor, but independently stopping prescribed medication on the basis of garlic supplements is not responsible (PMID 39275211, 26764326).
Based on multiple meta-analyses and systematic reviews of RCTs (up to 39 studies, up to 2300 participants). One study had manufacturer funding. Older data (2002) differs from more recent findings. No long-term endpoint studies (cardiovascular disease, mortality) are available.