Benefits
Blood pressure: modest reduction in pooled randomized trials
A meta-analysis of 12 randomized trials (819 adults) found systolic pressure about 3.9 mmHg lower overall and about 4.8/2.5 mmHg lower in people with high blood pressure, and a graded meta-analysis of 30 olive leaf and pomace trials also found lower pressure with olive leaf. In the largest trial, 621 adults already on treatment, 24-hour systolic pressure fell more than on placebo.
Vascular function: a short-term signal only
In a single-dose crossover trial in 18 healthy adults, olive leaf extract lowered a finger-pulse measure of arterial stiffness over the following hours compared with control. In a 6-week trial in 60 men with blood pressure slightly above normal, vascular function and arterial stiffness measures did not change.
Insulin sensitivity: one positive trial, glucose not improved in pooled data
In a 12-week crossover trial in 46 overweight middle-aged men, olive leaf capsules improved insulin sensitivity by about 15 percent versus placebo. A 14-week trial in adults with type 2 diabetes reported lower HbA1c, but a 24-week pilot trial did not, and three meta-analyses found no significant effect on glycemic markers.
Cholesterol and triglycerides: results differ between trials
In 60 men with blood pressure slightly above normal, a liquid extract lowered total and LDL cholesterol and triglycerides versus control over 6 weeks, and pooled trials show a small triglyceride drop. But an 8-week placebo-controlled trial in 77 overweight adults with mildly raised cholesterol found no lipid effect, and a review pooling parallel trials found none, giving mixed results overall.
Immune support: fewer sick days in one small trial
In a 9-week randomized trial in 32 high school athletes, a daily olive leaf extract tablet supplying 100 mg oleuropein did not change how often they developed upper respiratory illness, but they had about 28 percent fewer sick days than on placebo. This is one small trial and needs confirmation.
Inflammation and oxidation markers: inconsistent results
One 6-week trial lowered the inflammatory messenger IL-8, while a 12-week trial raised fasting IL-6 and left CRP and TNF-alpha unchanged. One meta-analysis found no change in inflammatory markers and a later graded one found lower TNF-alpha. Urinary oxidative stress markers and oxidized LDL did not change in two trials.
Gum pocket depth after dental cleaning (one small trial)
In a 4-month placebo-controlled trial in adults aged 50 and over with gum disease, all receiving non-surgical dental cleaning, capsules of an extract standardized to 40 percent oleuropein led to greater reductions in gum pocket depth and gains in gum attachment at several tooth sites. Only 43 of 60 people finished.
Extract strength varies between products
Daily oleuropein in trials ranged from about 51 mg to about 200 mg, and extracts ranged from about 16 to 40 percent oleuropein. Because each result came from a specific extract at a specific dose, comparing products by oleuropein per serving is more useful than comparing milligrams of extract.
Mechanism of action
ACE inhibition by olive leaf compounds (laboratory data)
In test tube assays, a water extract of olive leaves inhibited angiotensin-converting enzyme (ACE), part of the body's blood pressure regulating system. The active compound isolated was oleacein; oleuropein itself showed no significant inhibition until it was broken down by enzymes. Whether this occurs at supplement doses in people is not known.
Muscle glucose uptake (cell and mouse studies)
In muscle cells, oleuropein increased glucose uptake without insulin by activating the energy sensor AMPK, which moved the glucose transporter GLUT4 to the cell surface; it also increased GLUT4 at the membrane in muscles of mice fed a high fat diet. These laboratory findings may relate to the insulin sensitivity signal seen in one human trial.
LDL oxidation (test tube data)
In test tube studies, oleuropein protected LDL cholesterol particles from copper-induced oxidation, a process linked to artery wall changes. In people, oxidized LDL did not differ from placebo in an 8-week olive leaf extract trial or a 12-week crossover trial.
Clinical trials
Multicenter randomized, double-blind, placebo-controlled trial in Tunisia. The primary outcome was the change in 24-hour systolic and diastolic blood pressure from baseline to week 12. The abstract does not state the extract, its dose or its maker; one author is from Belpharma Laboratories. (Lamti et al. 2025, Journal of Hypertension)
621 adults already being treated for high blood pressure (307 on the extract, 314 on placebo).
The abstract reports a 6.4 mmHg fall in 24-hour systolic pressure from baseline on the extract and a figure of 1.5 mmHg for placebo (P < 0.01), without making clear whether 1.5 is the placebo group's change or the gap between groups. High readings over 24 hours fell on the extract only. The authors also report lower glucose, triglycerides, CRP and body weight, and no significant adverse events.
Double-blind, randomized, parallel trial after a 4-week run-in. Participants took 500 mg of the EFLA943 olive leaf extract twice daily (1,000 mg/day) or an active comparator, the blood pressure drug captopril; there was no placebo group. The primary outcome was the fall in systolic pressure at week 8. A later meta-analysis lists the trial as manufacturer funded. (Susalit et al. 2011, Phytomedicine)
Adults aged 20 to 65 in Indonesia with stage 1 hypertension; 179 randomized and 148 analyzed (72 extract, 76 comparator).
Systolic pressure fell 11.5 mmHg and diastolic 4.8 mmHg from baseline on the extract, and the difference from the comparator group was not statistically significant. Without a placebo group, the trial cannot show how much of the fall came from the extract itself. Triglycerides fell significantly within the extract group only.
Randomized, double-blind, controlled crossover trial with a 4-week washout. Participants took 10 ml twice daily of Comvita's liquid olive leaf extract (136 mg oleuropein and 6 mg hydroxytyrosol per day) or a polyphenol-free control for 6 weeks each. Blood pressure was the primary outcome; Comvita provided half the funding. (Lockyer et al. 2017, European Journal of Nutrition)
60 men, average age 45, with blood pressure slightly above normal (systolic 121 to 140 or diastolic 81 to 90 mmHg).
Compared with control, daytime systolic pressure was about 4.0 mmHg lower and 24-hour systolic about 3.3 mmHg lower, partly because pressure rose during the control phase. Total and LDL cholesterol, triglycerides and IL-8 were also lower. Vascular function, arterial stiffness, other inflammation markers and glucose measures did not change.
Randomized, double-blind, placebo-controlled trial (NCT02990637) at Maastricht University. Participants took 500 mg/day of a water-based olive leaf extract (16.7 percent oleuropein, 83.5 mg/day) supplied by Interquim SA, or a maltodextrin placebo, for 8 weeks. Blood lipids were the primary outcome. BioActor partly funded the study and employed the first author. (Stevens et al. 2021, European Journal of Nutrition)
77 overweight or obese adults, average age 56, with mildly raised total cholesterol (5.0 to 8.0 mmol/L); 74 completed.
The trial was null: blood lipids did not differ from placebo at 4 or 8 weeks, and there were no significant differences in oxidized LDL, blood pressure, glucose, insulin or liver function.
Randomized, double-blind, placebo-controlled crossover trial in New Zealand with a 6-week washout. Participants took four Comvita olive leaf extract capsules daily (51.1 mg oleuropein and 9.7 mg hydroxytyrosol) or placebo for 12 weeks each. The primary outcome was insulin sensitivity (Matsuda index). Comvita supplied the products and co-funded the grant. (de Bock et al. 2013, PLoS One)
46 overweight middle-aged men (average age about 46) at risk of metabolic syndrome.
Insulin sensitivity was about 15 percent higher and pancreatic beta-cell responsiveness about 28 percent higher than on placebo, and glucose during a glucose tolerance test was about 6 percent lower. Fasting IL-6 rose. Lipids, 24-hour blood pressure, body composition, carotid wall thickness and liver function did not change.